How to Use a Multimeter


So… how do I use a multimeter? This tutorial will show you how to use a digital multimeter (DMM), an indispensable tool that you can use to diagnose circuits, learn about other people’s electronic designs, and even test a battery. Hence the ‘multi’-‘meter’ (multiple measurement) name.

The most basic things we measure are voltage and current. A multimeter is also great for some basic sanity checks and troubleshooting. Is your circuit not working? Does the switch work? Put a meter on it! The multimeter is your first defense when troubleshooting a system. In this tutorial we will cover measuring voltage, current, resistance and continuity.

Parts of a Multimeter

multimeter parts

A multimeter is has three parts:

  • Display
  • Selection Knob
  • Ports

The display usually has four digits and the ability to display a negative sign. A few multimeters have illuminated displays for better viewing in low light situations.

The selection knob allows the user to set the multimeter to read different things such as milliamps (mA) of currentvoltage (V) and resistance (Ω).

Two probes are plugged into two of the ports on the front of the unit. COM stands for common and is almost always connected to Ground or ‘-’ of a circuit. The COM probe is conventionally black but there is no difference between the red probe and black probe other than color. 10A is the special port used when measuring large currents (greater than 200mA). mAVΩ is the port that the red probe is conventionally plugged in to. This port allows the measurement of current (up to 200mA), voltage (V), and resistance (Ω). The probes have a banana type connector on the end that plugs into the multimeter. Any probe with a banana plug will work with this meter. This allows for different types of probes to be used.

using a multimeter

Using a Multimeter to test the voltage on a LiPo Battery.

Probe Types

There are many different types of probes available for multimeters. Here are a few of our favorites:

  • Banana to Alligator Clips : These are great cables for connecting to large wires or pins on a breadboard. Good for performing longer term tests where you don’t have to have to hold the probes in place while you manipulate a circuit.
  • Banana to IC Hook : IC hooks work well on smaller ICs and legs of ICs.
  • Banana to Tweezers : Tweezers are handy if you are needing to test SMD components.
  • Banana to Test Probes : If you ever break a probe, they are cheap to replace!

Measuring Voltage

To start, let’s measure voltage on a AA battery: Plug the black probe into COM and the red probe into mAVΩ. Set the multimeter to “2V” in the DC (direct current) range. Almost all portable electronics use direct current), not alternating current. Connect the black probe to the battery’s ground or ‘-’ and the red probe to power or ‘+’. Squeeze the probes with a little pressure against the positive and negative terminals of the AA battery. If you’ve got a fresh battery, you should see around 1.5V on the display (this battery is brand new, so its voltage is slightly higher than 1.5V).

If you’re measuring DC voltage (such as a battery or a sensor hooked up to an Arduino) you want to set the knob where the V has a straight line. AC voltage (like what comes out of the wall) can be dangerous, so we rarely need to use the AC voltage setting (the V with a wavy line next to it). If you’re messing with AC, we recommend you get a non-contact testerrather than use a digital multimeter.

Volts DC

Use the V with a straight line to measure DC Voltage

Volts AC

Use the V with a wavy line to measure AC Voltage

What happens if you switch the red and black probes? The reading on the multimeter is simply negative. Nothing bad happens! The multimeter measures voltage in relation to the common probe. How much voltage is there on the ‘+’ of the battery compared to common or the negative pin? 1.5V. If we switch the probes, we define ‘+’ as the common or zero point. How much voltage is there on the ‘-’ of the battery compared to our new zero? -1.5V!

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Now let’s construct a simple circuit to demonstrate how to measure voltage in a real world scenario. The circuit is simply a 1kΩ and a Blue super bright LED powered with a SparkFun Breadboard Power Supply Stick. To begin, let’s make sure the circuit you are working on is powered up correctly. If your project should be at 5V but is less than 4.5V or greater than 5.5V, this would quickly give you an indication that something is wrong and you may need to check your power connections or the wiring of your circuit.

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Measuring the voltage coming off of a Power Supply Stick.

Set the knob to “20V” in the DC range (the DC Voltage range has a V with a straight line next to it). Multimeters are generally not autoranging. You have to set the multimeter to a range that it can measure. For example, 2V measures voltages up to 2 volts, and 20V measures voltages up to 20 volts. So if you’ve measuring a 12V battery, use the 20V setting. 5V system? Use the 20V setting. If you set it incorrectly, you will probably see the meter screen change and then read ‘1’.

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With some force (imagine poking a fork into a piece of cooked meat), push the probes onto two exposed pieces of metal. One probe should contact a GND connection. One probe to the VCC or 5V connection.

We can test different parts of the circuit as well. This practice is called nodal analysis, and it is a basic building block in circuit analysis. By measuring the voltage across the circuit we can see how much voltage each component requires. Let’s measure the whole circuit first. Measuring from where the voltage is going in to the resistor and then where ground is on the LED, we should see the full voltage of the circuit, expected to be around 5V.

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We can then see how much voltage the LED is using. This is what is referred to as the voltage drop across the LED. If that doesn’t make sense now, fear not. It will as you explore the world of electronics more. The important thing to take away is that different parts of a circuit can be measured to analyze the circuit as a whole.

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This LED is using 2.66V of the available 5V supply to illuminate. This is lower than the forward voltage stated in the datasheet on account of the circuit only having small amount of current running though it, but more on that in a bit.


What happens if you select a voltage setting that is too low for the voltage you’re trying to measure? Nothing bad. The meter will simply display a 1. This is the meter trying to tell you that it is overloaded or out-of-range. Whatever you’re trying to read is too much for that particular setting. Try changing the multimeter knob to a the next highest setting.

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Reading the 5V across this circuit is too much for the 2V setting on the multimeter.

Selection Knob

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Why does the meter knob read 20V and not 10V? If you’re looking to measure a voltage less than 20V, you turn to the 20V setting. This will allow you to read from 2.00 to 19.99.

The first digit on many multimeters is only able to display a ‘1’ so the ranges are limited to 19.99 instead of 99.99. Hence the 20V max range instead of 99V max range.

Warning! In general, stick to DC circuits (the settings on the multimeter with straight lines, not curvy lines). Most multimeters can measure AC (alternating current) systems, but AC circuits can be dangerous. A wall outlet with AC or ‘main voltage’ is the stuff that can zap you pretty good. VERY carefully respect AC. If you need to check to see if an outlet is ‘on’ then use a AC tester. Really the only times we’ve needed to measure AC are when we’ve got an outlet that is acting funny (is it really at 110V?), or if we’re trying to control a heater (such as a hot plate). Go slow and double check everything before you test an AC circuit.

Measuring Resistance

Normal resistors have color codes on them. If you don’t know what they mean, that’s ok! There are plenty of online calculators that are easy to use. However, if you ever find yourself without internet access, a multimeter is very handy at measuring resistance.

Pick out a random resistor and set the multimeter to the 20kΩ setting. Then hold the probes against the resistor legs with the same amount of pressure you when pressing a key on a keyboard.

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The meter will read one of three things, 0.001, or the actual resistor value.

  • In this case, the meter reads 0.97, meaning this resistor has a value of 970Ω, or about 1kΩ (remember you are in the 20kΩ or 20,000 Ohm mode so you need to move the decimal three places to the right or 970 Ohms).
  • If the multimeter reads 1 or displays OL, it’s overloaded. You will need to try a higher mode such as 200kΩ mode or 2MΩ (megaohm) mode. There is no harm if this happen, it simply means the range knob needs to be adjusted.
  • If the multimeter reads 0.00 or nearly zero, then you need to lower the mode to 2kΩ or 200Ω.

Remember that many resistors have a 5% tolerance. This means that the color codes may indicate 10,000 Ohms (10kΩ), but because of discrepancies in the manufacturing process a 10kΩ resistor could be as low as 9.5kΩ or as high as 10.5kΩ. Don’t worry, it’ll work just fine as a pull-up or general resistor.

Let’s drop the meter down to the next lowest setting, 2KΩ. What happens?

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Not a whole lot changed. Because this resistor (a 1KΩ) is less than 2KΩ, it still shows up on the display. However, you’ll notice that there is one more digit after the decimal point giving us a slightly higher resolution in our reading. What about the next lowest setting?

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Now, since 1kΩ is greater than 200Ω, we’ve maxed out the meter, and it is telling you that it is overloaded and that you need to try a higher value setting.

As a rule of thumb, it’s rare to see a resistor less than 1 Ohm. Remember that measuring resistance is not perfect. Temperature can affect the reading a lot. Also, measuring resistance of a device while it is physically installed in a circuit can be very tricky. The surrounding components on a circuit board can greatly affect the reading.

Measuring Current

Reading current is one of the trickiest and most insightful readings in the world of embedded electronics. It’s tricky because you have to measure current in series. Where voltage is measure by poking at VCC and GND (in parallel), to measure current you have to physically interrupt the flow of current and put the meter in-line. To demonstrate this, we’ll use the same circuit we used in the measuring voltage section.

The first thing we’ll need is an extra piece of wire. As mentioned, we’ll need to physically interrupt the circuit to measure the current. Said another way, pull out the VCC wire going to the resistor, add a wire where that wire was connected, and then probe from the power pin on the power supply to the resistor. This effectively “breaks” power to the circuit. We then insert the multimeter in-line so that it can measure the current as it “flows” through to the multimeter into the bread board.

For these pictures, we cheated and used alligator clips. When measuring current, it’s often good to watch what your system does over time, for a few seconds or minutes. While you might want to stand there and hold the probes to the system, sometimes it’s easier to free up your hands. These alligator clip probes can come in handy. Note that almost all multimeters have the same sized jacks (they’re called “banana plugs”) so if you’re in a pinch, you can use your friend’s probes.

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With the multimeter connected, we can now set the dial to the proper setting and measure some current. Measuring current works the same as voltage and resistance – you have to get the correct range. Set the multimeter to 200mA, and work from there. The current consumption for many breadboard projects is usually under 200mA. Make sure the red probe is plugged into the 200mA fused port. On our favorite multimeter, the 200mA hole is the same port/hole as voltage and resistance reading (the port is labeled mAVΩ). This means you can keep the red probe in the same port to measure current, voltage, or resistance. However, if you suspect that your circuit will be using close to or more than 200mA, switch your probe to the 10A side, just to be safe. Overloading the current can result in a blown fuse rather than just an overload display. More on that in a bit.

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This circuit was only pulling 1.8mA at the time of measurement, not a lot of current. The average reading was closer to 2.1mA.

Realize that the multimeter is acting as a piece of wire – you’ve now completed the circuit, and the circuit will power on. This is important because as time goes on the LED, microcontroller, sensor, or whatever device being measured may change its power consumption (such as turning on an LED can resulting in a 20mA increase for a second, then decrease for a second when it turns off). On the multimeter display you should see the instantaneous current reading. All multimeters take readings over time and then give you the average, so expect the reading to fluctuate. In general, cheaper meters will average more harshly and respond more slowly, so take each reading with a grain of salt. In your head, take an average range such as 7 to 8mA under normal 5V conditions (not 7.48mA).

Similar to the other measurements, when measuring current, the color of the probes does not matter. What happens if we switch probes? Nothing bad happens! It simply causes the current reading to become negative:

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Current is still flowing through the system, you’ve just changed your perspective and now the meter reads negative.

Remember! When you’re done using the meter, always return the meter to read voltage (return the probes to the voltage port, set the meter to read the DC voltage range if necessary). It’s common to grab a meter and begin to quickly measure the voltage between two pins. If you have left your meter in ‘current’ mode, you won’t see the voltage on the display. Instead you’ll see ‘0.000’ indicating that there is no current between VCC and GND. Within that split second you will have connected VCC to GND through your meter and the 200mA fuse will blow = not good. So before you put the meter down for the night, remember to leave your meter in a friendly state.

Measuring current can be tricky the first couple of times. Don’t worry if you blow the fuse – we’ve done it dozens of times! We’ll show you how to replace the fuse in a later section.


Continuity testing is the act of testing the resistance between two points. If there is very low resistance (less than a few Ωs), the two points are connected electrically, and a tone is emitted. If there is more than a few Ωs of resistance, than the circuit is open, and no tone is emitted. This test helps insure that connections are made correctly between two points. This test also helps us detect if two points are connected that should not be.

Continuity is quite possibly the single most important function for embedded hardware gurus. This feature allows us to test for conductivity of materials and to trace where electrical connections have been made or not made.

Set the multimeter to ‘Continuity’ mode. It may vary among DMMs, but look for a diode symbol with propagation waves around it (like sound coming from a speaker).

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Multimeter is set to continuity mode.

Now touch the probes together. The multimeter should emit a tone (Note: Not all multimeters have a continuity setting, but most should). This shows that a very small amount of current is allowed to flow without resistance (or at least a very very small resistance) between probes.

Warning! In general, turn OFF the system before checking for continuity.

On a breadboard that is not powered, use the probes to poke at two separate ground pins. You should hear a tone indicating that they are connected. Poke the probes from the VCC pin on a microcontroller to VCC on your power supply. It should emit a tone indicating that power is free to flow from the VCC pin to the micro. If it does not emit a tone, then you can begin to follow the route that copper trace takes and tell if there are breaks in the line, wire, breadboard, or PCB.

Continuity is a great way to test if two SMD pins are touching. If your eyes can’t see it, the multimeter is usually a great second testing resource.

When a system is not working, continuity is one more thing to help troubleshoot the system. Here are the steps to take:

  1. If the system is on, carefully check VCC and GND with the voltage setting to make sure the voltage is the correct level. If the 5V system is running at 4.2V check your regulator carefully, it could be very hot indicating the system is pulling too much current.
  2. Power the system down and check continuity between VCC and GND. If there is continuity (if you hear a beep), then you’ve got a short somewhere.
  3. Power the system down. With continuity, check that VCC and GND are correctly wired to the pins on the microcontroller and other devices. The system may be powering up, but the individual ICs may be wired wrong.
  4. Assuming you can get the microcontroller running, set the multimeter aside, and move on to serial debugging or use a logic analyzer to inspect the digital signals.

Continuity and large capacitors: During normal troubleshooting. you will be probing for continuity between ground and the VCC rail. This is a good sanity check before powering up a prototype to make sure there is not a short on the power system. But don’t be surprised if you hear a short ‘beep!’ when probing. This is because there is often significant amounts of capacitance on the power system. The multimeter is looking for very low resistance to see if two points are connected. Capacitors will act like a short for a split second until they fill up with energy, and then act like an open connection. Therefore, you will hear a short beep and then nothing. That’s ok, it’s just the caps charging up.

Changing the Fuse

One of the most common mistakes with a new multimeter is to measure current on a bread board by probing from VCC to GND (bad!). This will immediately short power to ground through the multimeter causing the bread board power supply to brown out. As the current rushes through the multimeter, the internal fuse will heat up and then burn out as 200mA flows through it. It will happen in a split second and without any real audible or physical indication that something is wrong.

Wow, that was neat. Now what? Well first, remember that measuring current is done in series (interrupt the VCC line to the breadboard or microcontroller to measure current). If you try to measure the current with a blown fuse, you’ll probably notice that the meter reads ‘0.00’ and that the system doesn’t turn on like it should when you attach the multimeter. This is because the internal fuse is broken and acts as a broken wire or open. Don’t worry, this happens all the time, and it costs about $1 to fix.

To change the fuse, find your handy dandy mini screw driver, and start taking out screws. The SparkFun DMM is pretty easy to pull apart. Start by removing the battery plate and the battery.

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Next, remove the two screws hiding behind the battery plate.

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Lift the face of the multimeter slightly.

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Now notice the hooks on the bottom edge of the face. You will need to slide the face sideways with a little force to disengage these hooks.

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Once the face is unhooked, it should come out easily. Now you can see inside the multimeter!

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Gently lift up on the fuse, and it will pop out.

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Make sure to replace the correct fuse with the correct type. In other words, replace the 200mA fuse with a 200mA fuse.

Warning! DO NOT put a 10A fuse where a 200mA fuse should go. The placement of the fuses may not match the placement of the probe ports. Read the metal cap on either end of the fuse to double check which is which.

The components and PCB traces inside the multimeter are designed to take different amounts of current. You will damage and possibly ruin your multimeter if you accidentally push 5A through the 200mA port.

There are times where you need to measure high current devices like a motor or heating element. Do you see the two places to put the red probe on the front of the multimeter? 10A on the left and mAVΩ on the right? If you try to measure more than 200mA on the mAVΩ port you run the risk of blowing the fuse. But if you use the 10A port to measure current, you run a much lower risk of blowing the fuse. The trade-off is sensitivity. As we talked about above, by using the 10A port and knob setting, you will only be able to read down to 0.01A or 10mA. Most of my systems use more than 10mA so the 10A setting and port works well enough. If you’re trying to measure very low power (micro or nano amps) the 200mA port with the 2mA, 200uA, or 20uA could be what you need.

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Remember: If your system has the potential to use more than 100mA you should start with the red probe plugged into the 10A port and 10A knob setting.

With sub $50 digital multimeters, the measurements you are likely to take are just trouble shooting readings, not scientific experimental results. If you really need to see how the IC uses current or voltage over time, use an Agilent or other high quality bench unit. These units have higher precision and offer a wide range of fancy functions (some include Tetris!). Bunnie Huang, hardware designer behind Chumby, uses high-precision current readings to trouble shoot boards during the final testing procedures of a Chumby. By looking at the current consumption of different boards that have failed (for example a given failed board uses 210mA over the normal), he could identify what was wrong with the board (when the RAM fails, it generally uses 210mA over normal). By pinpointing what may be potentially wrong, the rework and repair of boards is made much easier.

What Makes a Good Multimeter?

Everyone has his or her preference, but in general multimeters that have continuity are preferred. Every other feature is just icing on the cake.

Agilent Meter

There are fancy multimeters that are autoranging, meaning they automatically change their internal range to attempt to find the correct voltage, resistance, or current of the thing you’re poking at. Auto-ranging can be very helpful if you know how to use it. Generally speaking, autoranging multimeters are higher quality and generally have more features. So if someone gives you a multimeter with auto-range, put it to use! Just know how to get it into manual mode. A circuit’s voltage or current can fluctuate quite quickly. With some of the systems, the current or voltage is so sporadic that the auto-range can’t keep up sensibly.

back-lit LCD is fancy, but when was the last time you measured your circuit in the dark? We generally steer clear of scary forests and situations that require us to test stuff in the middle of the night, but some people may want or need a dark-friendly multimeter.

good click on the range selector is actually a major plus in our book. A soft knob is usually indicative of a shoddy meter.

Decent probes are a plus. Over time the leads will tend to break down at the flex point. We’ve seen wires come completely out of probes – and it’s always at the moment you need the probes to work! If you do break a probe, they are reasonably cheap to replace.

Auto-off is a great feature that is rarely seen on cheaper multimeters. This is a feature that can benefit beginners and advanced users alike, as it’s easy to forget to turn the meter off at 2AM. The SparkFun digital multimeter doesn’t have this feature, but luckily the meter is very low-power. We’ve left the multimeter for two days straight before the 9V battery began to get low. That said, don’t forget to turn your meter off!

You’re now ready to use your digital multimeter to start measuring the world around you. Feel free to start using it to answer many questions. I believe my LED is getting 20mA, is it really? How much voltage does a lemon have? Is a glass of water conductive? Can I use aluminum foil to replace these wires? A digital multimeter will answer these and many more questions about electronics.


Source : sparkfun electronics

How to Read a Schematic


Schematics are our map to designing, building, and troubleshooting circuits. Understanding how to read and follow schematics is an important skill for any electronics engineer.

This tutorial should turn you into a fully literate schematic reader! We’ll go over all of the fundamental schematic symbols:

Schematic component overview

Then we’ll talk about how those symbols are connected on schematics to create a model of a circuit. We’ll also go over a few tips and tricks to watch out for.

Suggested Reading

Schematic comprehension is a pretty basic electronics skill, but there are a few things you should know before you read this tutorial. Check out these tutorials, if they sound like gaps in your growing brain:

Schematic Symbols (Part 1)

Are you ready for a barrage of circuit components? Here are some of the standardized, basic schematic symbols for various components.


The most fundamental of circuit components and symbols! Resistors on a schematic are usually represented by a few zig-zag lines, with two terminals extending outward. Schematics using international symbols may instead use a featureless rectangle, instead of the squiggles.

Resistor schematic symbols

Potentiometers and Variable Resistors

Variable resistors and potentiometers each augment the standard resistor symbol with an arrow. The variable resistor remains a two-terminal device, so the arrow is just laid diagonally across the middle. A potentiometer is a three-terminal device, so the arrow becomes the third terminal (the wiper).

Variable resistor symbols


There are two commonly used capacitor symbols. One symbol represents a polarized (usually electrolytic or tantalum) capacitor, and the other is for non-polarized caps. In each case there are two terminals, running perpendicularly into plates.

Capacitors symbols

The symbol with one curved plate indicates that the capacitor is polarized. The curved plate represents the cathode of the capacitor, which should be at a lower voltage than the positive, anode pin. A plus sign might also be added to the positive pin of the polarized capacitor symbol.


Inductors are usually represented by either a series of curved bumps, or loopy coils. International symbols may just define an inductor as a filled-in rectangle.

Inductor symbols


Switches exist in many different forms. The most basic switch, a single-pole/single-throw (SPST), is two terminals with a half-connected line representing the actuator (the part that connects the terminals together).

Switch symbol

Switches with more than one throw, like the SPDT and SP3T below, add more landing spots for the the actuator.

SPDT and SP3T symbols

Switches with multiple poles, usually have multiple, alike switches with a dotted line intersecting the middle actuator.

DPDT symbol

Power Sources

Just as there are many options out there for powering your project, there are a wide variety of power source circuit symbols to help specify the power source.

DC or AC Voltage Sources

Most of the time when working with electronics, you’ll be using constant voltage sources. We can use either of these two symbols to define whether the source is supplying direct current (DC) or alternating current (AC):

Voltage source symbols


Batteries, whether they’re those cylindrical, alkaline AA’s or rechargeable lithium-polymers, usually look like a pair of disproportionate, parallel lines:

Battery symbols

More pairs of lines usually indicates more series cells in the battery. Also, the longer line is usually used to represent the positive terminal, while the shorter line connects to the negative terminal.

Voltage Nodes

Sometimes – on really busy schematics especially – you can assign special symbols to node voltages. You can connect devices to these one-terminal symbols, and it’ll be tied directly to 5V, 3.3V, VCC, or GND (ground). Positive voltage nodes are usually indicated by an arrow pointing up, while ground nodes usually involve one to three flat lines (or sometimes a down-pointing arrow or triangle).

Voltage node symbols

Schematic Symbols (Part 2)


Basic diodes are usually represented with a triangle pressed up against a line. Diodes are also polarized, so each of the two terminals require distinguishing identifiers. The positive, anode is the terminal running into the flat edge of the triangle. The negative, cathode extends out of the line in the symbol (think of it as a – sign).

Diode symbol

There are a all sorts of different types of diodes, each of which has a special riff on the standard diode symbol. Light-emitting diodes (LEDs) augment the diode symbol with a couple lines pointing away. Photodiodes, which generate energy from light (basically, tiny solar cells), flip the arrows around and point them toward the diode.

LED and Photodiode symbols

Other special types of diodes, like Schottky’s or zeners, have their own symbols, with slight variations on the bar part of the symbol.

Schottky and zener diode symbols


Transistors, whether they’re BJTs or MOSFETs, can exist in two configurations: positively doped, or negatively doped. So for each of these types of transistor, there are at least two ways to draw it.

Bipolar Junction Transistors (BJTs)

BJTs are three-terminal devices; they have a collector (C), emitter (E), and a base (B). There are two types of BJTs – NPNs and PNPs – and each has its own unique symbol.

NPN and PNP BJT symbols

The collector (C) and emitter (E) pins are both in-line with each other, but the emitter should always have an arrow on it. If the arrow is pointing inward, it’s a PNP, and, if the arrow is pointing outward, it’s an NPN. A mnemonic for remembering which is which is “NPN: not pointing in.”

Metal Oxide Field-Effect Transistors (MOSFETs)

Like BJTs, MOSFETs have three terminals, but this time they’re named source (S), drain (D), and gate (G). And again, there are two different versions of the symbol, depending on whether you’ve got an n-channel or p-channel MOSFET. There are a number of commonly used symbols for each of the MOSFET types:

Variety of MOSFET symbols

The arrow in the middle of the symbol (called the bulk) defines whether the MOSFET is n-channel or p-channel. If the arrow is pointing in means it’s a n-channel MOSFET, and if it’s pointing out it’s a p-channel. Remember: “n is in” (kind of the opposite of the NPN mnemonic).

Digital Logic Gates

Our standard logic functions – AND, OR, NOT, and XOR – all have unique schematic symbols:

Standard logic functions

Adding a bubble to the output negates the function, creating NANDs, NORs, and XNORs:

Negated logic gates

They may have more than two inputs, but the shapes should remain the same (well, maybe a bit bigger), and there should still only be one output.

Integrated Circuits

Integrated circuits accomplish such unique tasks, and are so numerous, that they don’t really get a unique circuit symbol. Usually, an integrated circuit is represented by a rectangle, with pins extending out of the sides. Each pin should be labeled with both a number, and a function.

ATmega328, ATSHA204, and ATtiny45 IC symbols

Schematic symbols for an ATmega328 microcontroller (commonly found on Arduinos), an ATSHA204 encryption IC, and an ATtiny45 MCU. As you can see, these components greatly vary in size and pin-counts.

Because ICs have such a generic circuit symbol, the names, values and labels become very important. Each IC should have a value precisely identifying the name of the chip.

Unique ICs: Op Amps, Voltage Regulators

Some of the more common integrated circuits do get a unique circuit symbol. You’ll usually see operation amplifiers laid out like below, with 5 total terminals: a non-inverting input (+), inverting input (-), output, and two power inputs.

Op amp symbols

Often, there will be two op amps built into one IC package requiring only one pin for power and one for ground, which is why the one on the right only has three pins.

Simple voltage regulators are usually three-terminal components with input, output and ground (or adjust) pins. These usually take the shape of a rectangle with pins on the left (input), right (output) and bottom (ground/adjust).

Voltage regulator symbols


Crystals and Resonators

Crystals or resonators are usually a critical part of microcontroller circuits. They help provide a clock signal. Crystal symbols usually have two terminals, while resonators, which add two capacitors to the crystal, usually have three terminals.

Crystal and resonator symbols

Headers and Connectors

Whether it’s for providing power, or sending out information, connectors are a requirement on most circuits. These symbols vary depending on what the connector looks like, here’s a sampling:

Connector symbols

Motors, Transformers, Speakers, and Relays

We’ll lump these together, since they (mostly) all make use of coils in some way. Transformers (not the more-than-meets-the-eye kind) usually involve two coils, butted up against each other, with a couple lines separating them:

Transformer symbols

Relays usually pair a coil with a switch:

Relay symbol

Speakers and buzzers usually take a form similar to their real-life counterparts:


And motors generally involve an encircled “M”, sometimes with a bit more embellishment around the terminals:


Fuses and PTCs

Fuses and PTCs – devices which are generally used to limit large inrushes of current – each have their own unique symbol:

Fuse and PTC symbol

The PTC symbol is actually the generic symbol for a thermistor, a temperature-dependent resistor (notice the international resistor symbol in there?).

No doubt, there are many circuit symbols left off this list, but those above should have you 90% literate in schematic reading. In general, symbols should share a fair amount in common with the real-life components they model. In addition to the symbol, each component on a schematic should have a unique name and value, which further helps to identify it.

Name Designators and Values

One of the biggest keys to being schematic-literate is being able to recognize which components are which. The component symbols tell half the story, but each symbol should be paired with both a name and value to complete it.

Names and Values

Values help define exactly what a component is. For schematic components like resistors, capacitors, and inductors the value tells us how many ohms, farads, or henries they have. For other components, like integrated circuits, the value may just be the name of the chip. Crystals might list their oscillating frequency as their value. Basically, the value of a schematic component calls out its most important characteristic.

Component names are usually a combination of one or two letters and a number. The letter part of the name identifies the type of component – R’s for resistors, C’s for capacitors, U’s for integrated circuits, etc. Each component name on a schematic should be unique; if you have multiple resistors in a circuit, for example, they should be named R1, R2, R3, etc. Component names help us reference specific points in schematics.

The prefixes of names are pretty well standardized. For some components, like resistors, the prefix is just the first letter of the component. Other name prefixes are not so literal; inductors, for example, are L’s (because current has already taken I [but it starts with a C…electronics is a silly place]). Here’s a quick table of common components and their name prefixes:

Name Identifier Component
R Resistors
C Capacitors
L Inductors
S Switches
D Diodes
Q Transistors
U Integrated Circuits
Y Crystals and Oscillators

Although theses are the “standardized” names for component symbols, they’re not universally followed. You might see integrated circuits prefixed with IC instead of U, for example, or crystals labeled as XTAL’s instead of Y’s. Use your best judgment in diagnosing which part is which. The symbol should usually convey enough information.

Reading Schematics

Understanding which components are which on a schematic is more than half the battle towards comprehending it. Now all that remains is identifying how all of the symbols are connected together.

Nets, Nodes and Labels

Schematic nets tell you how components are wired together in a circuit. Nets are represented as lines between component terminals. Sometimes (but not always) they’re a unique color, like the green lines in this schematic:

Example of nets on a schematic

Junctions and Nodes

Wires can connect two terminals together, or they can connect dozens. When a wire splits into two directions, it creates a junction. We represent junctions on schematics with nodes, little dots placed at the intersection of the wires.

A node

Nodes give us a way to say that “wires crossing this junction are connected”. The absences of a node at a junction means two separate wires are just passing by, not forming any sort of connection. (When designing schematics, it’s usually good practice to avoid these non-connected overlaps wherever possible, but sometimes it’s unavoidable).

Example of connected an disconnected nodes

Net Names

Sometimes, to make schematics more legible, we’ll give a net a name and label it, rather than routing a wire all over the schematic. Nets with the same name are assumed to be connected, even though there isn’t a visible wire connecting them. Names can either be written directly on top of the net, or they can be “tags”, hanging off the wire.

Linked name tags

Each net with the same name is connected, as in this schematic for an FT231X Breakout Board. Names and labels help keep schematics from getting too chaotic (imagine if all those nets were actually connected with wires).

Nets are usually given a name that specifically states the purpose of signals on that wire. For example, power nets might be labeled “VCC” or “5V”, while serial communication nets might be labeled “RX” or “TX”.

Schematic Reading Tips

Identify Blocks

Truly expansive schematics should be split into functional blocks. There might be a section for power input and voltage regulation, or a microcontroller section, or a section devoted to connectors. Try recognizing which sections are which, and following the flow of circuit from input to output. Really good schematic designers might even lay the circuit out like a book, inputs on the left side, outputs on the right.

Example of a sectioned schematic

If the drawer of a schematic is really nice (like the engineer who designed this schematic for the RedBoard), they may separate sections of a schematic into logical, labeled blocks.

Recognize Voltage Nodes

Voltage nodes are single-terminal schematic components, which we can connect component terminals to in order to assign them to a specific voltage level. These are a special application of net names, meaning all terminals connected to a like-named voltage node are connected together.

Annotated voltage node example

Like-named voltage nodes – like GND, 5V, and 3.3V – are all connected to their counterparts, even if there aren’t wires between them.

The ground voltage node is especially useful, because so many components need a connection to ground.

Reference Component Datasheets

If there’s something on a schematic that just doesn’t make sense, try finding a datasheet for the most important component. Usually the component doing the most work on a circuit is an integrated circuit, like a microcontroller or sensor. These are usually the largest component, oft-located at the center of the schematic.

PCB Basics


One of the key concepts in electronics is the printed circuit board or PCB. It’s so fundamental that people often forget to explain what a PCB is. This tutorial will breakdown what makes up a PCB and some of the common terms used in the PCB world.

Blank PCB from the ClockIt Kit

Over the next few pages, we’ll discuss the composition of a printed circuit board, cover some terminology, a look at methods of assembly, and discuss briefly the design process behind creating a new PCB.

Suggested Reading

Before you get started you may want to read up on some concepts we build upon in this tutorial:


Minh Tuấn was kind enough to translate this tutorial to Vietnamese. You can view the translation here.

What’s a PCB?

Printed circuit board is the most common name but may also be called “printed wiring boards” or “printed wiring cards”. Before the advent of the PCB circuits were constructed through a laborious process of point-to-point wiring. This led to frequent failures at wire junctions and short circuits when wire insulation began to age and crack.

Mass of wire wrap
courtesy Wikipedia user Wikinaut

A significant advance was the development of wire wrapping, where a small gauge wire is literally wrapped around a post at each connection point, creating a gas-tight connection which is highly durable and easily changeable.

As electronics moved from vacuum tubes and relays to silicon and integrated circuits, the size and cost of electronic components began to decrease. Electronics became more prevalent in consumer goods, and the pressure to reduce the size and manufacturing costs of electronic products drove manufacturers to look for better solutions. Thus was born the PCB.

LilyPad PCB

PCB is an acronym for printed circuit board. It is a board that has lines and pads that connect various points together. In the picture above, there are traces that electrically connect the various connectors and components to each other. A PCB allows signals and power to be routed between physical devices. Solder is the metal that makes the electrical connections between the surface of the PCB and the electronic components. Being metal, solder also serves as a strong mechanical adhesive.


A PCB is sort of like a layer cake or lasagna- there are alternating layers of different materials which are laminated together with heat and adhesive such that the result is a single object.

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Let’s start in the middle and work our way out.


The base material, or substrate, is usually fiberglass. Historically, the most common designator for this fiberglass is “FR4”. This solid core gives the PCB its rigidity and thickness. There are also flexible PCBs built on flexible high-temperature plastic (Kapton or the equivalent).

You will find many different thickness PCBs; the most common thickness for SparkFun products is 1.6mm (0.063″). Some of our products- LilyPad boards and Arudino Pro Micro boards- use a .8mm thick board.

Perf board

Cheaper PCBs and perf boards (shown above) will be made with other materials such as epoxies or phenolics which lack the durability of FR4 but are much less expensive. You will know you are working with this type of PCB when you solder to it – they have a very distictive bad smell. These types of substrates are also typically found in low-end consumer electronics. Phenolics have a low thermal decomposition temperature which causes them to delaminate, smoke and char when the soldering iron is held too long on the board.


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PCB with copper exposed, no solder mask or silkscreen.

The next layer is a thin copper foil, which is laminated to the board with heat and adhesive. On common, double sided PCBs, copper is applied to both sides of the substrate. In lower cost electronic gadgets the PCB may have copper on only one side. When we refer to a double sided or 2-layer board we are referring to the number of copper layers (2) in our lasagna. This can be as few as 1 layer or as many as 16 layers or more.

The copper thickness can vary and is specified by weight, in ounces per square foot. The vast majority of PCBs have 1 ounce of copper per square foot but some PCBs that handle very high power may use 2 or 3 ounce copper. Each ounce per square translates to about 35 micrometers or 1.4 thousandths of an inch of thickness of copper.


The layer on top of the copper foil is called the soldermask layer. This layer gives the PCB its green (or, at SparkFun, red) color. It is overlaid onto the copper layer to insulate the copper traces from accidental contact with other metal, solder, or conductive bits. This layer helps the user to solder to the correct places and prevent solder jumpers.

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In the example above green solder mask is applied to the majority of the PCB, covering up the small traces but leaving the the silver rings and SMD pads exposed so they can be soldered to.

Soldermask is most commonly green in color but nearly any color is possible. We use red for almost all the SparkFun boards, white for the IOIO board, and purple for the LilyPad boards.


PCB with silkscreen

The white silkscreen layer is applied on top of the soldermask layer. The silkscreen adds letters, numbers, and symbols to the PCB that allow for easier assembly and indicators for humans to better understand the board. We often use silkscreen labels to indicate what the function of each pin or LED.

Silkscreen is most commonly white but any ink color can be used. Black, gray, red, and even yellow silkscreen colors are widely available; it is, however, uncommon to see more than one color on a single board.


Now that you’ve got an idea of what a PCB structure is, let’s define some terms that you may hear when dealing with PCBs:

  • Annular ring – the ring of copper around a plated through hole in a PCB.

Annular ring on resistor Annular ring on vias

Examples of annular rings.

  • DRC – design rule check. A software check of your design to make sure the design does not contain errors such as traces that incorrectly touch, traces too skinny, or drill holes that are too small.
  • Drill hit – places on a design where a hole should be drilled, or where they actually were drilled on the board. Inaccurate drill hits caused by dull bits are a common manufacturing issue.

Bad drill hits

Not so accurate, but functional drill hits.

  • Finger – exposed metal pads along the edge of a board, used to create a connection between two circuit boards. Common examples are along the edges of computer expansion or memory boards and older cartridge-based video games.
  • Mouse bites – an alternative to v-score for separating boards from panels. A number of drill hits are clustered close together, creating a weak spot where the board can be broken easily after the fact. See the SparkFun Protosnap boards for a good example.

LilyPad Protosnap with mouse bites

Mouse bites on the LilyPad ProtoSnap allow the PCB to be snapped apart easily.

  • Pad – a portion of exposed metal on the surface of a board to which a component is soldered.

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PTH (plated through-hole) pads on the left, SMD (surface mount device) pads on the right.

  • Panel – a larger circuit board composed of many smaller boards which will be broken apart before use. Automated circuit board handling equipment frequently has trouble with smaller boards, and by aggregating several boards together at once, they process can be sped up significantly.
  • Paste stencil – a thin, metal (or sometimes plastic) stencil which lies over the board, allowing solder paste to be deposited in specific areas during assembly.

Abe does a quick demonstration of how to line up a paste stencil and apply solder paste.

  • Pick-and-place – the machine or process by which components are placed on a circuit board.

Bob shows us the SparkFun MyData Pick and Place machine. It’s pretty awesome.

  • Plane – a continuous block of copper on a circuit board, define by borders rather than by a path. Also commonly called a “pour”.

PCB ground pour

Various portions of the PCB that have no traces but has a ground pour instead.

  • Plated through hole – a hole on a board which has an annular ring and which is plated all the way through the board. May be a connection point for a through hole component, a via to pass a signal through, or a mounting hole.

Plated through hole resistor

A PTH resistor inserted into the FabFM PCB, ready to be soldered. The legs of the resistor go through the holes. The plated holes can have traces connected to them on the front of the PCB and the rear of the PCB.

  • Pogo pin – spring-loaded contact used to make a temporary connection for test or programming purposes.

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The popular pogo pin with pointed tip. We use tons of these on our test beds.

  • Reflow – melting the solder to create joints between pads and component leads.
  • Silkscreen – the letters, number, symbols and imagery on a circuit board. Usually only one color is available, and resolution is usually fairly low.

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Silkscreen identifying this LED as the power LED.

  • Slot – any hole in a board which is not round. Slots may or may not be plated. Slots sometimes add to add cost to the board because they require extra cut-out time.

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Complex slots cut into the ProtoSnap – Pro Mini. There are also many mouse bites shown. Note: the corners of the slots cannot be made completely square because they are cut with a circular routing bit.

  • Solder paste – small balls of solder suspended in a gel medium which, with the aid of a paste stencil, are applied to the surface mount pads on a PCB before the components are placed. During reflow, the solder in the paste melts, creating electrical and mechanical joints between the pads and the component.

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Solder paste on a PCB shortly before the components are placed. Be sure to read about paste stencil above as well.

  • Solder pot – a pot used to quickly hand solder boards with through hole components. Usually contains a small amount of molten solder into which the board is quickly dipped, leaving solder joints on all exposed pads.
  • Soldermask – a layer of protective material laid over the metal to prevent short circuits, corrosion, and other problems. Frequently green, although other colors (SparkFun red, Arduino blue, or Apple black) are possible. Occasionally referred to as “resist”.

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Solder mask covers up the signal traces but leaves the pads to solder to.

  • Solder jumper – a small, unwanted blob of solder connecting two adjacent pins on a component on a circuit board.
  • Surface mount – construction method which allows components to be simply set on a board, not requiring that leads pass through holes in the board. This is the dominant method of assembly in use today, and allows boards to be populated quickly and easily.
  • Thermal – a small trace used to connect a pad to a plane. If a pad is not thermally relieved, it becomes difficult to get the pad to a high enough temperature to create a good solder joint. An improperly thermally relieved pad will feel “sticky” when you attempt to solder to it, and will take an abnormally long time to reflow.

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On the left, a solder pad with two small traces (thermals) connecting the pin to the ground plane. On the right, a via with no thermals connecting it completely to the ground plane.

  • Thieving – hatching, gridlines, or dots of copper left in areas of a board where no plane or traces exist. Reduces difficulty of etching because less time in the bath is required to remove unneeded copper.
  • Trace – a continuous path of copper on a circuit board.

Traces on PCB

A small trace connecting the Reset pad to elsewhere on the board. A larger, thicker trace connects to the 5V power pin.

  • V-score– a partial cut through a board, allowing the board to be easily snapped along a line.
  • Via – a hole in a board used to pass a signal from one layer to another. Tented vias are covered by soldermask to protect them from being soldered to. Vias where connectors and components are to be attached are often untented (uncovered) so that they can be easily soldered.

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Front and back of the same PCB showing a tented via. This via brings the signal from the front side of the PCB, through the middle of the board, to the back side.

  • Wave solder – a method of soldering used on boards with through-hole components where the board is passed over a standing wave of molten solder, which adheres to exposed pads and component leads.

Designing your own!

How do you go about designing your own PCB? The ins and outs of PCB design are way too in depth to get into here, but if you really want to get started, here are some pointers:

  1. Find a CAD package: there are a lot of low-cost or free options out there on the market for PCB design. Things to consider when choosing a package:
    • Community support: are there a lot of people using the package? The more people using it, the more likely you are to find ready-made libraries with the parts you need.
    • Ease-of-use: if it’s painful to use it, you won’t.
    • Capability: some programs place limitations on your design- number of layers, number of components, size of board, etc. Most of them allow you to pay for a license to upgrade their capability.
    • Portability: some free programs do not allow you to export or convert your designs, locking you in to one supplier only. Maybe that’s a fair price to pay for convenience and price, maybe not.
  2. Look at other people’s layouts to see what they have done. Open Source Hardware makes this easier than ever.
  3. Practice, practice, practice.
  4. Maintain low expectations. Your first board design will have lots of problems. Your 20th board design will have fewer, but will still have some. You’ll never get rid of them all.
  5. Schematics are important. Trying to design a board without a good schematic in place first is an exercise in futility.

Finally, a few words on the utility of designing your own circuit boards. If you plan on making more than one or two of a given project, the payback on designing a board is pretty good- point-to-point wiring circuits on a protoboard is a hassle, and they tend to be less robust than purpose-designed boards. It also allows you to sell your design if it turns out to be popular.

How to Power a Project


This tutorial will cover the various ways you can power your electronic projects. It will go into some detail about voltage and current considerations you may want to make. It will also go into the extra considerations you have to make if your project is mobile/remote or, in other words, not going to be sitting next to a wall power outlet.

If this is truly your first electronic project, you have the option of reading through this tutorial or sticking with the recommended supply for the project or development board of your choice. The SparkFun Inventor’s Kit contains the USB cable you need for power and works fine for all the projects in the kit as well as many more advanced projects. If you’re feeling overwhelmed, that kit is the best place to start.

Suggested Reading

Here are related tutorials you may want to check out before reading this one:

Ways to Power a Project

Here are some of the most methods used for powering a project:

  • AC to DC power supplies (like a computer or laptop would use)
  • Variable DC bench power supply
  • Batteries
  • Via a USB cable

Left to Right: AC/DC power adapter, bench supply, battery, USB cable

Four common ways to supply power to your project

Which option should I pick to power my project?

The answer to this question largely depends on your project specific requirements.

If you’re starting off with the SparkFun Inventor’s Kit or another basic development board, you will likely just need a USB cable. The Arduino Uno is an example that requires only a USB A to B cable to supply the power to run the example circuits in the kit.

If you’re in the business of building projects and testing circuits regularly, acquiring a variable DC bench power supplyis highly recommended. This will allow you to set the voltage to a specific value depending on what you need for your project. It also buys you some protection as you can set a maximum current allowed. Then, if there is a short circuit in your project, the bench supply will shut down hopefully preventing harm to some components in your project.

A specific AC to DC power supply is often used after a circuit is proven. This option is also great if you often use the same development board again and again in your projects. These wall adapters usually have a set voltage and current output, so it’s important to make sure that the adapter you choose has the correct specifications as the project you will be powering and to not exceed those specifications.

If you want your project to be mobile or based in a remote location away from where you can gather AC wall power from the grid, batteries are the answer you’re looking for. Batteries come in a huge variety so be sure to check out the later parts of this tutorial so you can figure out precisely what to choose. Common choices include rechargeable NiMH AA’s and lithium polymer ion.

Voltage/Current Considerations

How much voltage do I need for project X?

This depends largely on the circuit, so there is no easy answer to this question. However, most microprocessor development boards like the Arduino Uno have a voltage regulator on board. This allows us to supply a voltage in a specified range above the regulated voltage. A lot of microprocessors and IC’s on development boards run at 3.3 or 5 Volts but have voltage regulators that can handle anywhere from 6V to 12V.

The power comes from a power supply and is then regulated closely by a voltage regulator so that each chip is powered at a consistent voltage even when the current draw may fluctuate at different times. Here at SparkFun, we use 9V power supplies for many of our products that operate in the 3.3V to 5V range. However, to verify what voltages are safe, it is recommended that you check the datasheet for the voltage regulator on the development board to see what voltage range is recommended by the manufacturer.

How much current do I need for project X?

This question also depends on the development board and microprocessor you’re using as well as what circuits you plan on connecting to it. If your power supply cannot give you the amount of juice the project needs, the circuit may start acting in a strange, unpredictable way. This is also known as a brown-out.

As with voltage, it’s recommended to check the datasheets and estimate what the different bits and pieces of the circuit might need. It’s also better practice to round up and assume your circuit will need more current than to not provide enough current. If your circuit includes elements that require massive amounts of current, like motors or large amounts of LEDs, you may need a large supply or even separate supplies for the microprocessor and the extra motors. Again, it’s always in your best interest to get a power supply rated for a higher current and not use the extra than to have a supply that can’t provide enough.

Have no idea how much current your project draws?

Once you’ve been playing with circuits for a while, it will be easier to estimate the amount of current your project requires. However, the common ways to figure it out experimentally are to either use a variable DC power supply that has a readout for current or to use a digital multimeter to measure the current going to your circuit while it’s running. If you don’t know how to measure current with a multimeter, please see our multimeter tutorial.

For your voltage and current measuring needs

Digital Multimeter

We highly recommend having a DMM in your electronics toolbox. It’s great for measuring current or voltage.


How do I connect my battery or power supply to my circuit?

There are many ways to actually connect a power supply to your project.

Left to right: banana jacks, wire hookup, barrel jack, battery case, JST

Common ways to connect a power to your circuit

Variable benchtop power supplies commonly connect to circuits using banana jacks or wires directly. These are also similar to the connectors found on the multimeter probe cables.

Many projects are built on a breadboard first, as a prototype, before they become a final product. There are numerous ways to power your breadboard circuit, many of them involving a the same connectors mentioned here.

Once a project is past the prototyping phase, it will usually end up on a PCB. One of the most common power connectors used on a finished PCB, in both consumer electronics and hobby electronics alike, is the barrel connector, also know as a barrel jack. These can vary in size, but they all function the same and provide a simply, reliable way to power your project.

Batteries are generally held in a case that holds the batteries and connects the the circuit via wires or a barrel jack. Some batteries like Lithium Polymer Ion batteries often use a JST connector.

To learn more about different power connectors, please see our connectors tutorial.

Remote/Mobile Power

Which battery should I choose?

When you’re powering a remote circuit, the same issues of finding a battery that delivers the proper voltage and current still apply. Battery life, or capacity, is a measure of total charge the battery contains. The capacity of a battery is usually rated in ampere-hours (Ah) or milliampere-hours (mAh), and it tells you how many amps a fully charged battery can supply over a period of one hour. For example, a 2000mAh battery can supply up to 2A (2000mA) for one hour.

Battery size, shape, and weight is also something to consider when making your project mobile, especially if it’s going to be on something that flies like a small quad-copter. You can get a rough idea of the variety by visiting this wikipedia list. Learn more about battery types in our battery technology tutorial.

Batteries in series and parallel

You can add batteries in series or parallel to produce the desired voltage and current needed for your project. When two or more batteries are placed in series, the voltages of the batteries are added together. For example, lead-acid car batteries are actually made out of six single-cell lead acid batteries tied together in series; the six 2.1V cells add up to produce 12.6V. When tying two batteries in series, it’s recommended that they be of the same chemistry. Also be wary of charging batteries in series as many chargers are limited to single-cell charging.

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When you connect two or more batteries in parallel, the capacities add. For example, four AA batteries connected in parallel will still produce 1.5V, however the capacity of the batteries will be quadrupled.

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How much battery capacity do I need for my project?

This question is easier to answer once you have determined the amount of current that your circuit normally draws. In the following example, we will use estimation. However, it is encouraged that you measure current draw of your circuit using a Digital Multimeter to get accurate results.

As an example, let’s start with a circuit, estimate its current output, then select a battery and calculate how long it the circuit will run on battery power. Let’s choose a ATmega 328 microcontroller to be our brains for the circuit. It draws about 20mA under normal conditions. Let’s now connect three red LED’s and the standard 330 ohm current limiting resistors to digital I/O pins of the microcontroller. In that configuration, each LED added makes the circuit draw about 10mA more current. Now let’s connect two Micro Metal motors to the microcontroller as well. Each one of these uses approximately 25mA when turned on. Our total possible current draw is now:

Calculating Circuit Current Draw

Let’s choose a standard alkaline AA battery for this because it has more than enough current capability (up to 1A), has a decent battery capacity (usually in the range of 1.5 Ah to 2.5Ah), and is very common. We’ll assume the average is 2Ah for this example. The downside to using a AA is it only has a 1.5V output, and, since the rest of our components will run on 5V, we need to step up the voltage. We can use this 5V step-up breakout to get the voltage we need, or we can use three AA batteries in series to get us close to the voltage we need. Three AA’s in series gives us a voltage of 4.5 V (3 times 1.5V). You could also add another battery for a total of 6V and regulate the voltage down to what your circuit requires.

To calculate how long a circuit will last on battery power, we use the following equation:

The equation for calculating battery life

For a circuit powered by 3 AA’s in parallel that’s connected to a circuit with a constant 100mA current draw, this translates to:

We would ideally get 60 hours of battery life out of these three alkaline AA’s in this parallel configuration. However, it’s good practice to ‘derate’ batteries, which means to assume you’re going to get less than ideal battery life. Let’s conservatively say that we’ll get 75% of the ideal battery life, and therefore about 45 hours of battery life for our project.

Battery life can also vary based on the actual current draw amount. Here’s a graph from an Energizer AA battery showing its expected battery life based on constant current draw.

Energizer AA E91 Specifications

Energizer AA, Current vs Battery Life

This is just one of the numerous configurations you could use to power your project remotley.

tinyAVR Microcontrollers

Key Features

  • Small — Atmel tinyAVR devices are designed specifically for applications where size and cost are critical. The smallest tinyAVR MCU measures only 1.5mm x 1.4mm. You can employ it as a single-chip solution in small systems. Or use it to deliver glue logic and distributed intelligence in larger systems.
  • Capacitive Touch — The Atmel QTouch® Library makes it simple to embed capacitive-touch button, slider, and wheel functionality into general-purpose Atmel AVR® microcontroller applications. The royalty-free QTouch Library provides several library files for each device and supports different numbers of touch channels, enabling both flexibility and efficiency in touch application.
  • Fast and code efficient — The AVR CPU gives the tinyAVR devices the same high performance as larger Atmel AVR devices, and several times the processing power of any similarly-sized competitor. Flexible and versatile, they feature high code efficiency that makes them ideal for a broad range of applications.
  • High integration — Each pin has multiple uses as I/O, ADC, and PWM. Even the reset pin can be reconfigured as an I/O pin. Some tinyAVR devices feature a Universal Serial Interface (USI), which can be used as SPI, UART or TWI, while others have dedicated hardware for these serial interfaces.
  • 0.7V operation — Where most microcontrollers require 1.8V or more to operate, the tinyAVR with boost regulator boosts the voltage from a single AA or AAA battery into a stable 3V supply to power the entire application.

8-bit AVR Microcontroller, 512B Flash, 6/8-pin

8-bit AVR Microcontroller, 512B Flash, 6/8-pin, ADC

8-bit AVR Microcontroller, 1KB Flash, 6/8-pin

8-bit AVR Microcontroller, 1KB Flash, 6/8-pin, ADC

8-bit AVR Microcontroller, 1KB Flash, 8-pin, high-performance analog peripherals

8-bit AVR Microcontroller, 1KB Flash, 14-pin, high-performance analog peripherals

8-bit AVR Microcontroller, 1KB Flash, 8/10/20-pin

8-bit picoPower AVR Microcontroller, 1KB Flash, 8/10/20-pin

8-bit AVR Microcontroller, 2KB Flash, 14/15/20-pin

8-bit AVR Microcontroller, 2KB Flash, 14/20-pin

8-bit picoPower AVR Microcontroller, 2KB Flash, 14/15/20-pin

8-bit AVR Microcontroller, 2KB Flash, 8/20-pin

8-bit AVR Microcontroller, 2KB Flash, 20/32-pin

8-bit AVR Microcontroller, 2KB Flash, 28/32-pin

8-bit AVR Microcontroller, 4KB Flash, 20-pin

8-bit AVR Microcontroller, 4KB Flash, 20-pin Boost Converter (0.7V Operation)

8-bit AVR Microcontroller, 4KB Flash, 14/20-pin

8-bit picoPower AVR Microcontroller, 4KB Flash, 14/15/20-pin

8-bit AVR Microcontroller, 4KB Flash, 8/20-pin

8-bit picoPower AVR Microcontroller, 4KB Flash, 28/32-pin

8-bit AVR Microcontroller, 8KB Flash, 14/20-pin

8-bit picoPower AVR Microcontroller, 8KB Flash, 14/20-pin

8-bit AVR Microcontroller, 8KB Flash, 8/20-pin

8-bit AVR Microcontroller, 8KB Flash, 20/32-pin, LIN Controller

8-bit picoPower AVR Microcontroller, 8KB Flash, 28/32-pin

8-bit AVR Microcontroller, 16KB Flash, 20/32-pin, LIN Controller

8-bit picoPower AVR Microcontroller, 2KB Flash, 20/32-pin

8-bit picoPower AVR Microcontroller, 4KB Flash, 14/20-pin

8-bit AVR Microcontroller, 4KB Flash, 20/32-pin

8-bit picoPower AVR Microcontroller, 2KB Flash, 20/32-pin

8-bit AVR Microcontroller, 8KB Flash, 32-pin

8-bit picoPower AVR Microcontroller, 8KB Flash, 14/20-pin

8-bit AVR Microcontroller, 8KB Flash, 20/32-pin

8-bit picoPower AVR Microcontroller, 8KB Flash, 20/32-pin

8-bit picoPower AVR Microcontroller, 16KB Flash, 20-pin

8-bit AVR Microcontroller, 2KB Flash, 20-pin

8-bit picoPower AVR Microcontroller, 2KB Flash, 20-pin

8-bit picoPower AVR Microcontroller, 4KB Flash, 20-pin


SMD resistor code calculator

This simple calculator will help you determine the value of any SMD resistor. To get started, input the 3 or 4 digit code and hit the “Calculate” button or Enter.

Note: The program was tested rigorously, but it still may have a few bugs. So, when in doubt (and when it’s possible) don’t hesitate to use a multimeter to double-check the critical components.

See also the color code calculator on this page for MELF and standard through-hole resistors.

How to calculate the value of an SMD resistor

Most chip resistors are marked with a 3-digit or 4-digit code — the numerical equivalent of the familiar color code for through-hole components. Recently, a new coding system (the EIA-96) has appeared on precision SMDs.

The 3-digit code

Standard-tolerance SMD resistors are marked with a simple 3-digit code. The first two numbers will indicate the significant digits, and the third will be the multiplier, telling you the power of ten to which the two significant digits must be multiplied (or how many zeros to add). Resistances of less than 10 ohms do not have a multiplier, the letter ‘R’ is used instead to indicate the position of the decimal point.

3-digit code examples:

220 = 22 × 100 (1) = 22Ω (not 220Ω!)
471 = 47 × 101 (10) = 470Ω
102 = 10 × 102 (100) = 1000Ω or 1kΩ
3R3 = 3.3Ω

more 3-digit SMD resistor examples…

The 4-digit code

The 4-digit code is used for marking precision surface mount resistors. It’s similar to the previous system, the only difference is the number of significant digits: the first three numberswill tell us the significant digits, and the fourth will be the multiplier, indicating the power of ten to which the three significant digits must be multiplied (or how many zeros to add). Resistances of less than 100 ohms are marked with the help of the letter ‘R’, indicating the position of the decimal point.

4-digit code examples:

4700 = 470 × 100 (1) = 470Ω (not 4700Ω!)
2001 = 200 × 101 (10) = 2000Ω or 2kΩ
1002 = 100 × 102 (100) = 10000Ω or 10kΩ
15R0 = 15.0Ω

more 4-digit SMD resistor examples…


Recently, a new coding system (EIA-96) has appeared on 1% SMD resistors. It consists of a three character code: the first 2 numbers will tell us the 3 significant digits of the resistor value (see the lookup table below) and the third marking (a letter) will indicate the multiplier.

Code Multiplier
Z 0.001
Y or R 0.01
X or S 0.1
A 1
B or H 10
C 100
D 1000
E 10000
F 100000

EIA-96 code examples:

01Y = 100 × 0.01 = 1Ω
68X = 499 × 0.1 = 49.9Ω
76X = 604 × 0.1 = 60.4Ω
01A = 100 × 1 = 100Ω
29B = 196 × 10 = 1.96kΩ
01C = 100 × 100 = 10kΩ

more EIA-96 SMD examples…

Code Value Code Value Code Value Code Value
01 100 25 178 49 316 73 562
02 102 26 182 50 324 74 576
03 105 27 187 51 332 75 590
04 107 28 191 52 340 76 604
05 110 29 196 53 348 77 619
06 113 30 200 54 357 78 634
07 115 31 205 55 365 79 649
08 118 32 210 56 374 80 665
09 121 33 215 57 383 81 681
10 124 34 221 58 392 82 698
11 127 35 226 59 402 83 715
12 130 36 232 60 412 84 732
13 133 37 237 61 422 85 750
14 137 38 243 62 432 86 768
15 140 39 249 63 442 87 787
16 143 40 255 64 453 88 806
17 147 41 261 65 464 89 825
18 150 42 267 66 475 90 845
19 154 43 274 67 487 91 866
20 158 44 280 68 499 92 887
21 162 45 287 69 511 93 909
22 165 46 294 70 523 94 931
23 169 47 301 71 536 95 953
24 174 48 309 72 549 96 976


  • an SMD resistor with a marking of 0, 00, 000 or 0000 is a jumper (a zero-ohm link).
  • a chip resistor marked with the standard 3 digit code and a short bar below the marking denotes a precision (1% or less) resistor with a value taken from the E24 series (these values are usually reserved for 5% resistors). For example: 122 = 1.2kΩ 1%. Some manufacturers underline all three digits — do not confuse this with the code used on low value current sensing resistors.
  • SMDs with values in order of milliohms, made for current sensing applications are often marked with the help of the letter M or m, showing the decimal point location (with the value in milliohms). For example: 1M50 = 1.50mΩ, 2M2 = 2.2mΩ.
  • Current sensing SMDs can also be marked with a long bar on top (1m5 = 1.5mΩ, R001 = 1mΩ, etc.) or a long bar under the code (101 = 0.101Ω, 047 = 0.047Ω). The underline is used when the starting ‘R’ has to be omitted due to the limited space on the resistor’s body. So, for example, R068 becomes 068 = 0.068Ω (68mΩ).

Power rating

To find out the approximative power rating of your SMD resistor, measure its length and width. A few commonly used package dimensions with the corresponding typical power ratings are presented in the table below. Use this table as a guide only, and always consult the component’s datasheet for the exact value.

SMD resistor dimensions
Package Size in inches (L×W) Size in mm (L×W) Power rating
0201 0.024″ × 0.012″ 0.6 mm × 0.3 mm 1/20W
0402 0.04″ × 0.02″ 1.0 mm × 0.5 mm 1/16W
0603 0.063″ × 0.031″ 1.6 mm × 0.8 mm 1/16W
0805 0.08″ × 0.05″ 2.0 mm × 1.25 mm 1/10W
1206 0.126″ × 0.063″ 3.2 mm × 1.6 mm 1/8W
1210 0.126″ × 0.10″ 3.2 mm × 2.5 mm 1/4W
1812 0.18″ × 0.12″ 4.5 mm x 3.2 mm 1/3W
2010 0.20″ × 0.10″ 5.0 mm × 2.5 mm 1/2W
2512 0.25″ × 0.12″ 6.35 mm × 3.2 mm 1W


The standard 3 and 4 digit code does not give us a way to determine the SMD resistor’s tolerance.

In most cases, however, you’ll find that a surface mount resistor marked with the 3-digit codehas a tolerance of 5% and a resistor marked with 4-digit code or the new EIA-96 code has a tolerance of 1% or less.

There are many exceptions to this rule, so always check the manufacturer’s datasheet, especially if the component’s tolerance is critical for your application.

Testing semiconductors with multimeters

Before building any circuit is it a good idea to test every semiconductor you plan to use in the project. This a good practice especially when reusing components from old appliances. This short tutorial describes common procedures for testing of Si and Ge signal and rectifier diodes, zener diodes, LEDs, bipolar and mosfet transistors for common failures like shorts, leaks and opens.

DT-830B digital multimeter

Testing signal and rectifier diode junctions

A regular signal or rectifier diode should read a low resistance on an analog ohmmeter (set on the low ohms scale) when forward biased (negative lead on cathode, positive lead on anode) and nearly infinite ohms in the reverse bias direction. A germanium diode will show a lower resistance compared to a silicon diode in the forward direction. A bad diode will show near zero ohms(shorted) or open in both directions.

1n4007 diode

Note: often, analog multimeters have the polarity of their probes reversed from what you would expect from the color coding. Many of them will have the red lead negative with respect to the black one.

On a digital multimeter, using the normal resistance ranges, this test will usually show open for any semiconductor junction since the meter does not apply enough voltage to reach the value of the forward drop.

Fortunately almost every digital multimeter will have a diode test mode. Using this mode, a silicon diode should read a voltage drop between 0.5 to 0.8 V in the forward direction (negative lead on cathode, positive lead on anode) and open in reverse. For a germanium diode, the reading will be lower, around 0.2 – 0.4 V in the forward direction. A bad diode will read a very low voltage drop (if shorted) or open in both directions.

Note: small diode leaks in the reverse bias direction are rare, but they will often go unnoticed when using the diode test mode on the majority of digital multimeters. To make sure the diode is good, you should make one more measurement: using a high ohm range (2Mohm or higher) on your DMM, place the negative lead on the anode and the positive lead on the cathode. A good Si diode (the most common type of diode in today’s circuits) will usually read infinite ohms. An older Ge diode may have a much higher level of reverse leakage current, so it may show a non-infinite value. When in doubt, try to compare the reading with measurements done on a good diode of the same type.

Testing Zener diodes

Simple Zener tester circuit

For a quick diagnosis, a Zener diode junction can be verified like a normal diode as described above. But, to test for reverse breakdown zener voltage, you will need a simple power supply with a voltage greater than the expected value and a high value resistor.

Connect a high value resistor (to limit the current to a safe value) in series with the zener diode and apply the voltage in the reverse direction across the diode (anode to the negative). The voltage measured across the diode will be the breakdown or zener voltage.

Testing LEDs

Simple LED tester circuit

LED diodes usually have a forward voltage drop too high to test with most multimeters, so you should use a similar circuit as the one described above.

Make sure to use a power supply greater than 3V and a suitable current limiting series resistor. A small current of 1-10 mA will be enough to light most LEDs when connected in the circuit.

Testing bipolar transistors

The assumption made when testing transistors is that a transistor is just a pair of connected diodes. Therefore it can be tested for shorts, opens or leakage with a simple analog or digital multimeter. Gain, frequency response, etc. tests can be made only with expensive specialized instruments, but in most cases a simple test is all you’ll need when building simple hobby circuits.

NPN transistor

Note: some power transistors have built in damper diodes connected across C-E and resistors connected across B-E which will confuse these readings. Also, a few small signal transistors have built-in resistors in series with the base or other leads, making this simple test method useless. Darlington transistors can also show unusual voltage drops and resistances. When testing a transistor of this type you will need to compare with a known good transistor or check the specifications to be sure.

To test a bipolar transistor with a digital multimeter, take it out of circuit and make the following measurements using the diode test mode:

  • Connect the red (positive) lead to the base of the transistor. Connect the black (negative) lead to the emitter. A good NPN transistor will read a junction drop voltage of 0.4V to 0.9V. A good PNP transistor will read open.
  • Leave the red meter lead on the base and move the black meter lead to the collector – the reading should be almost the same as the previous test, open for PNP and a slightly lower voltage drop for NPN transistors.
  • Reverse the meter leads and repeat the test. This time, connect the black meter lead to the base of the transistor and the red lead to the emitter. A good PNP transistor will read ajunction drop voltage of 0.4V to 0.9V. A good NPN transistor will read open.
  • Leave the black meter lead on the base and move the red lead to the collector – the reading should be almost the same as the previous test, open for NPN and a slightly lower voltage dropfor PNP transistors.
  • Place one meter lead on the collector, the other on the emitter, then reverse. Both tests should read open for both NPN and PNP transistors.

A similar test can be made with an analog VOM using the low ohms scale. Only 2 of the 6 possible combinations (the B-E and B-C junctions in forward bias) should show a low resistance (anywhere from 100 ohms to several Kohms) and none of the resistances should be near 0 Ohms.

If you read a short circuit (zero ohms or a voltage drop of zero) between two leads, or the transistor fails any of the tests described above, it is bad and must be replaced.

If you get readings that do not make sense, try to compare them with measurements done on a good transistor of the same type.

Some analog multimeters have their probe colors reversed since this makes the internal circuitry easier to design. So, it’s a good idea to confirm and label the lead polarity of your instrument by making a few measurements in resistance (VOM) or diode test mode (DMM) using a known good diode. This will also show you what to expect for a reading of a forward biased junction.

Identifying the leads and polarity of unknown bipolar transistors

The type (PNP or NPN) and the lead arrangement of unmarked transistors can be determined easily using a digital or analog multimeter, if the transistor is seen as a pair of connected diodes. The collector and emitter can be identified knowing the fact that the doping for the B-E junction is always much higher than for the B-C junction, therefore, the forward voltage drop will be slightly higher. This will show up as a couple of millivolts difference on a digital multimeter’s diode test scale or a slightly higher resistance on an analog VoltOhmMeter.

First make the a few measurements between various leads. Soon you’ll identify a lead (theBase) that will show a forward voltage drop (on DMMs) or a low resistance (analog VOMs) combined with two other leads (the Emitter and Collector). Now that the Base is identified, observe carefully the voltage drops across B-E and B-C. The B-C junction will have a slightly less voltage drop (DMM) or a slightly lower resistance when using an analog ohmmeter.

Note: For every degree the transistor increases in temperature, the diode drops will decrease by a few millivolts. This change can be confusing when determining the B-E and B-C junctions. So, make sure you do not hold the transistor under test in your hand and leave enough time for it to cool down to room temperature after soldering!

If you arrived at this point, you already know the polarity of the transistor under test. If the negative lead (black lead connected to the COM on most digital multimeters) is placed on the Base when measuring the B-C and B-E voltage drops – you have a PNP transistor. Similarly – if the positive meter lead is placed on the base, you have a NPN transistor.

This procedure may sound complicated at first, but practicing on a few transistors with known leads will make things clearer in no time. It is a good habit to test every transistor before placing it into the circuit, as the datasheet is not always at hand, and misplacing the leads can have devastating results.

Testing MOSFETs

Field Effect Transistors are difficult to test with a multimeter, but “fortunately” when a power MosFet blows, it blows big time: all their leads will show in short circuit. 99% of bad MosFets will have GS, GD and DS shorted. In other words – everything will be connected together.

Note: When measuring a MosFet hold it by the case or the tab and don’t touch the metal parts of the test probes with any of the other MosFet’s terminals until needed. Do not allow a MosFet to come in contact with your clothes, plastic, etc. because of the high static voltages they can generate.

You’ll know a MosFet is good when the Gate has infinite resistance to both Drain and Source. Exceptions to this rule are FETs with protection circuitry – they may act like there is a diode shunting GS – a diode drop for gate reverse bias. Connecting Gate to Source should cause the Drain to Source act like a diode. Forward biasing GS with 5V and measuring DS in forward bias should yield very low ohms. In reverse bias, it will still act like a diode.

Another simple test procedure: connect the multimeter’s negative lead to the source of the MosFet. Touch the MosFet’s Gate with the meter’s positive lead. Move the positive probe to the Drain – you should get a low reading as the MosFet’s internal capacitance on the Gate has now been charged up by the meter and the device is turned-on. With the meter’s positive lead still connected to the Drain, touch the source and gate with your finger. The Gate will be discharged through your finger and the reading should go high, indicating a non-conductive device! This simple test is not fail proof, but it’s usually adequate.

Know About Electronic Components

(1) Resistor:
A resistor is a device that reduces current in a circuit by offering obstruction to the flow of electrical current. So if you connect an LED directly to a 3v battery and then connect it by adding a resistor in series. The brightness in the second case would be lower than the first one as the resistor in the second case would not allow much current to pass through thus reducing the brightness. Resistance is measured in ohms, kilo ohms and mega ohms.
(2) Capacitor:
A capacitor is a device that stores electricity inside it when it is supplied and gives it out in a circuit when there is a loss in electricity. It is like a rechargeable battery but there is a lot of difference between them. A capacitor can store a small amount of current and can charge instantly whereas a battery can store a large amount of current and takes a while to charge. There are many types of capacitors but the two common types are- electrolytic (polarized) and non electrolytic (non polarized). Capacitance is measured in pico farads, nano farads and micro farads.
(3) Transistor:
A transistor is a device that amplifies a small current applied on its base pin to produce a large current that flows between the collector and emitter pins. It does not create a large current but acts as a switch which when supplied a small current on the base pin, closes the switch (switches it on). There are two types of transistors- NPN and PNP.
(4) Integrated Circuit (IC):
An integrated circuit is a small package that is made for a particular task. It has a miniature inbuilt circuit that has many components inside it can perform a particular task. For example- a 555 ic is meant for timing circuits and LM386 is meant for amplifying audio signals. It is usually a small black chip with pins coming out. There are 3 pin ics as well as 32 pin ics and even more.
(5) Diode:
A diode is a device that allows current to flow only in one direction. This is the reason it has polarity and should be connected correctly for its proper functioning. It is used to prevent the reverse flow of current.
(6) Light Emitting Diode (LED):
A light emitting diode is a special type of diode that can emit light when electricity is passed through it. Like a diode, an led also allows current to flow only in one direction so to make it work it should be connected properly in a circuit. These days LEDs are preferred over lightbulbs as they consume much less electricity than bulbs and CFLs. They are available in different shapes, sizes and colors but being energy efficient, their cost is much high.
(7) Potentiometer:
A potentiometer or a variable resistor is a device that allows us to choose different resistances that may be required in a circuit. It has a knob that can be adjusted to produce a specific resistance.
(8) Light Dependent Resistor (LDR):
An LDR is a special type of resistor that changes its resistance according to the intensity of light falling on it. The resistance of an ldr increases when it is dark and decreases when the intensity of light falling on it is high.
(9) Infra-Red Receiver (IR receiver):
An IR receiver is a device that receives infrared light and gives an output depending on the signal received. It decodes and tells the type of signal received. It is present in all the devices that are controlled using IR remotes.
(10) Seven Segment Display:
A seven segment display is a device that is used to display digits and letters. It has usually a series of seven leds put in a certain odder to form an 8. All the digits can be displayed by lighting a certain number of leds. It also has an extra led for decimal point.

How to Solder – Through-hole Soldering


Soldering is one of the most fundamental skills needed to dabble in the world of electronics. The two go together like peas and carrots. And, although it is possible to learn about and build electronics without needing to pick up a soldering iron, you’ll soon discover that a whole new world is opened with this one simple skill. We here at SparkFun believe that soldering should be a skill in everyone’s arsenal. In a world of increasing technological surroundings, we believe it is important that people everywhere be able to not only understand the technologies they use everyday but also be able to build, alter, and fix them as well. Soldering is one of many skills that will empower you to do just that.

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In this tutorial we will go over the basics of through-hole soldering – also known as plated through-hole soldering (PTH), discuss the tools needed, go over techniques for proper soldering, and show you where you can go from there. We will also discuss rework as it pertains to through-hole soldering and give you some tips and tricks that will make fixing any piece of electronics a breeze. This guide will be for beginners and experts alike. Whether you’ve never touched an iron before or are looking for a little refresher, this tutorial has a little something for everyone.

Suggested Reading

As stated earlier, you can learn about and build electronics without touching a soldering iron. If you would like to learn more about electronics theory before learning to solder, we recommend starting with some of these tutorials:

If you would like to know more about building circuits without needing to pick up a soldering iron, check out our solderless breadboard tutorial:

Lastly, we will be building upon some previous tutorials, so it is suggested that you read about and understand these subjects before moving forward in this tutorial:

If you’re all caught up on the above reading, let’s dive right in!

What is Solder?

Before learning how to solder, it’s always wise to learn a little bit about solder, its history, and the terminology that will be used while discussing it.

Solder, as a word, can be used in two different ways. Solder, the noun, refers to the alloy (a substance composed of two or more metals) that typically comes as a long, thin wire in spools or tubes. Solder, the verb, means to join together two pieces of metal in what is called a solder joint. So, we solder with solder!

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Solder wire sold as a spool (left) and in a tube (right). These come in both leaded and lead-free varieties.

Leaded vs. Lead-free Solder – A Brief History

One of the most important things to be aware of when it comes to solder is that, traditionally, solder was composed of mostly lead (Pb), tin (Sn), and a few other trace metals. This solder is known as leaded solder. As it has come to be known, lead is harmful to humans and can lead to lead poisoning when exposed to large amounts. Unfortunately, lead is also a very useful metal, and it was chosen as the go-to metal for soldering because of its low melting point and ability to create great solder joints.

With the adverse effects of leaded soldering known, some key individuals and countries decided it was best to not use leaded solder anymore. In 2006, the European Union adopted the Restriction of Hazardous Substances Directive(RoHS). This directive, stated simply, restricts the use of leaded solder (amongst other materials) in electronics and electrical equipment. With that, the use of lead-free solder became the norm in electronics manufacturing.

Lead-free solder is very similar to its leaded counterpart, except, as the name states, it contains no lead. Instead is is made up of mostly tin and other trace metals, such as silver and copper. This solder is usually marked with the RoHS symbol to let potential buyers know it conforms to the standard.

Choosing the Right Solder for the Job

When it comes to manufacturing electronics, it’s best to use lead-free solder to ensure the safety of your products. However, when it comes to you and your electronics, the choice of solder is yours to make. Many people still prefer the use of leaded solder on account of its superb ability to act as a joining agent. Still, others prefer safety over functionality and opt for the lead-free. SparkFun sells both varieties to allow individuals to make that choice for themselves.

Lead-free solder is not without its downfalls. As mentioned, lead was chosen because it performs the best in a situation such as soldering. When you take away the lead, you also take away some of the properties of solder that make it ideal for what it was intended – joining two pieces of metal. One such property is the melting point. Tin has a higher melting point than lead resulting in more heat needed to achieve flow. And, although tin gets the job done, it sometimes needs a little help. Many lead-free solder variants have what’s called a flux core. For now, just know that flux is a chemical agent that aids in the flowing of lead-free solder. While it is possible to use lead-free solder without flux, it makes it much easier to achieve the same effects as with leaded solder. Also, because of the added cost in making lead-free solder, it can sometimes be more expensive than leaded solder.

Aside from choosing leaded or lead-free solder, there are a number of other factors to consider when picking out solder. First, there are tons of other solder compositions out there aside from lead and tin. Check out the Wikipedia solder page for an extensive list of the different types. Second, solder comes in a variety of gauges, or widths. When working with small components, it’s often better to use a very thin piece of solder – the larger then number, the smaller the gauge. For large components, thicker wire is recommended. Last, solder comes in other forms besides wire. When getting into surface-mount soldering, you’ll see that solder paste is the form of choice. However, since this is a through-hole soldering tutorial, solder paste will not be discussed in detail.

Soldering Irons

There are many tools that aid in soldering, but none are more important than the soldering iron. If nothing else, you need at least an iron and some solder to accomplish the task at hand. Soldering irons come in a variety of from factors and range from simple to complex, but they all function roughly the same. Here, we’ll discuss the parts of an iron and the different types of irons.

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Soldering Iron Anatomy

Here are the basic parts that make up a soldering iron.

  • Soldering Tips – No iron is complete without an iron tip. The tip is the part of the iron that heats up and allows solder to flow around the two components being joined. Although solder will stick to the tip when applied, a common misconception is that the tip transfers the solder. The tip actually transfers heat, raising the temperature of the metal components to the melting point of the solder, and the solder melts accordingly. Most irons give you the option to change your tip, should you need to replace an old tip or if you need to switch to a different style of tip. Tips come in a variety of sizes and shapes to accommodate any component.


Several types of tips. From left to right, the bevel tip (aka hoof tip), two conical tips with varying widths, and the chisel tip.

Changing the tip is a simple process that consists of either unscrewing the wand or simply pushing in and pulling out the tip

changing the tip

  • Wand – The wand is the part of the iron that holds the tip. This is also the part that is handled by the user. Wands are usually made of a variety of insulating materials (such as rubber) to prevent the heat of the tip from transferring to the outside of the wand, but they also house wires and metal contacts that transfer heat from the base or outlet to the tip. This dual role of heating and preventing burns makes a high quality wand much appreciated.


Two varieties of wands. Notice how the tips screw into the wand allowing for interchangeability. Some wands have tips that simply push in and pull out without any attaching mechanism.

Some irons consist of just a wand that plugs into a wall outlet. These irons are as simple as they come, and they do not have any controls to vary the temperature. In these irons, the heating element is built directly into the wand.

wand iron

A simple soldering iron that consists of just the wand. Some of these irons do not offer interchangeable tips.

  • Base – The base of the soldering iron is the control box that allows the adjusting of temperatures. The wand attaches to the base and receives its heat from the electronics inside. There are analog bases, which have a dial that controls the temperature, and there are digital bases, which have buttons to set the temperature and a display that tells you the current temperature. Some bases even have extra features such as heat profiles that allow you to quickly change the amount of heat provided to the tip for soldering a variety of components.


Two variations of a soldering iron base. On the left, a digital base, complete with control buttons and a digital display. On the right, an analog base that uses a dial to control the temperature.

The base typically is comprised of a large transformer and several other control electronics that safely allow you to vary the heat of your tip.

inside iron

The insides of a soldering iron base

  • Stand (Cradle) – The iron stand (often referred to as a cradle) is what houses the iron when it is not in use. The stand may seem trivial, but leaving an unattended iron laying around on your desk or workbench is a potential hazard: it could burn you, or, worse, it could burn your desk and start a fire. Again, they can be as simple as ametal stand, or they can be complex, offering an auto-shutoff feature that reduces the temperature of the tip when the wand is placed in the cradle. This helps prevent the wearing of your tip over time.

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Different types of iron cradles. Notice some allow for a regular sponge while others hold a brass sponge.

  • Brass Sponge – As you solder, your tip will tend to oxidize, which means it will turn black and not want to accept solder. Especially with lead-free solder, there are impurities in the solder that tend to build up on the tip of your iron, which causes this oxidization. This is where the sponge comes in. Every so often you should give your tip a good cleaning by wiping off this build-up. Traditionally, an actual wet sponge was used to accomplish this. However, using a wet sponge can drastically reduce the lifespan of your tip. By wiping your tip on a cool, wet sponge, the tip tends to expand and contract from the change in temperature. This expansion and contraction will wear out your tip and can sometime cause a hole to develop in the side of the tip. Once a tip has a hole, it is no good for soldering. Thus, brass sponges have become the standard for tip cleaning. Brass sponges pull the excess solder from your tip while allowing the tip to maintain its current heat level. If you do not have a brass sponge, a regular sponge is better than nothing.

brass sponge

A brass sponge. If your iron stand doesn’t have a spot for a brass sponge, you can get one with its own base.

Soldering Accessories

Now that you know the ins and outs of a soldering iron, it’s time to discuss the other tools that will aid you on your soldering adventure.

  • Solder Wick – is the eraser to soldering’s pencil. When dealing with issues such as jumpers or the removal of parts (desoldering), solder wick comes in very handy. Solder wick – aka desoldering braid – is comprised of thin copper wire braided together. Solder is soaked (wicked) up by the copper allowing you to “erase” extra globs of solder.

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  • Tip Tinner – is a chemical paste used to clean the tip of your soldering iron. It is composed of a mild acid that helps remove baked on residue (like when you accidentally melt your tip on a component) and helps prevent oxidation (the nasty black stuff) that accumulates on your soldering tip when not in use.

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  • Flux Pen – Flux is a chemical agent that aids in the flowing of lead-free solder. Flux pens allow you to dab stubborn components with liquid flux to create better looking solder joints.

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  • Solder Vacuum (Solder Sucker) – is a great tool for removing solder left behind in through-holes when delsodering components. We’ll go over how to use this tool a little later in the tutorial.

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Other Suggested Tools

These tools aren’t necessary, but they sure do make soldering easier at times.

  • Third Hand (Third Arm) – Third hands are great for holding PCBs, wires, and components in place while you solder.
  • Flush Cutters – Cutters allow you to trim the legs of components you solder to the PCB.
  • Safety Glasses – just in case any clipped leads go flying.

Soldering Your First Component

Let’s put all these tools into action. This first video will go over the basics of soldering your first component – headers!

Check out the Vimeo version here.


It’s really that easy! Follow Dave’s simple rules to make every solder connection a good one.

  • Be cautious when handling hot irons
  • Use third hands or vices to hold boards while you solder
  • Set your iron at a good medium heat (325-375 degrees C)
  • If you see smoke coming from your solder, turn down the heat
  • Tin your tip with solder before each connection to help prep the joint
  • Use the side of the tip (aka the sweet spot), not the very tip of the iron
  • Heat both the pad and the part you want to solder evenly and at the same time
  • Pull the solder away, then the iron
  • A good solder joint should look like a volcano or Hersey kiss, not a ball or clump

We’ve also put together this digram to help you better understand what makes a good solder joint.

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Click for a larger image.

Advanced Techniques and Troubleshooting

Once you get the basics of creating good solder joints, it’s time to learn some of the more advanced PTH techniques that you can utilize. This video goes over using flux, removing solder jumpers, desoldering components, along with some other tips and tricks.

Here are some other tips for PTH soldering:

  • Desoldering can often be the best way to learn how to solder. There are many reasons to desolder a part: repair, upgrade, salvage, etc. Many of the techniques used in the video aid in the desoldering process.
  • There is another method of removing solder from through-holes that we refer to as the slap method.
  • If you’re ever unsure if the solder joint you created is making an electrical connection, you can use a multimeter to test for continuity.


When working with lead-free solder, flux tends to get everywhere, be it from the flux in the solder or from external flux applied by the user. Flux can corrode the PCB and components over time, thus it’s good to know how to clean your PCBs so they’re free of any flux residue. The simplest way to clean a board is to use a small brush (toothbrushes work great) and some isopropyl alcohol. If you are soldering more than a few boards, it may be necessary to clean them in batches. For this, we recommend a crock pot filled with distilled water. The distilled water keeps other impurities and contaminants away from your circuit.

It’s not 100% necessary to clean your board, however, it will increase the life of your circuit tremendously. For more information on PCB cleaning, click here.

Resources and Going Further

We’ve only just begun to travel down the soldering rabbit hole. Once you have mastered PTH soldering, you can try your hand at these other skills and tutorials.

And, of course, what’s a soldering tutorial without something to solder. SparkFun sells a variety of kits that are great for honing your soldering skills. There’s even a Learn to Solder series of kits that have all the tools necessary to get started.