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.