No previous electronic experience is required to have fun with this kit. Here are a few details about each component to make identifying, and perhaps understanding them, a bit easier. If at any point you are worried about how a component is used or why it's not working the internet offers a treasure trove of advice, or you can get help on our community support forums 

Identifying Resistors by Color Code

The graphic above is super useful for the Explorers guide - most CIRCs use them. Resistors have different values, consult this graphic if you get stuck later. If you want to get really good at identifying resistors quickly, play our fun iOS Game: Mho's Resistance

Lead Clipping

Some components in this kit come with very long wire leads. To make them more compatible with a breadboard a couple of changes can be made.


Clip the leads so the long lead is ~10mm (3/8”) long and the short one is ~7mm (9/32”). If you don't own clippers, you can pick up the CHP17 Flush Diagonal Cutters in the Adafruit shop


Bend the leads down so they are 90 degrees to the cylinder. You can do this precisely with Pliers or bending it against a 90 degree desk corner. 

Then snip them so they are ~6mm (1/4”) long.

Other Components:

Other components may need clipping. Use your discretion when doing so.

Identifying: TMP36 and NPN

While the TMP36 Analog Temperature Sensor and the NPN Transistor are similar, they perform very different tasks. To avoid mixing them up in your circuit, use these two pictures to identify which part you have:

Parts Field Guide

(all of these parts can be found in the Metro Experimenters kit, click the image to enlarge it)

Part Picture

Name & What does it do?

How to Identify

No. of Leads

What to look out for


LED: Emits light when a small current is passed through it. (only in one direction)

Looks like a mini light bulb.

2 (one longer, this one connects to positive)

Will only work in one direction.

Requires a current limiting resistor


Diode: The electronic equivalent of a one way valve. Allowing current to flow in one direction but not the other.

Usually a cylinder with wires extending from either end. (and an off center line indicating polarity)


Will only work in one direction (current will flow if end with the line is connected to ground)


Resistor: Restricts the amount of current that can flow through a circuit.

Cylinder with wires extending from either end. The value is displayed using a color coding system (for details see the "Identifying Resistors" section)


Easy to grab the wrong value (double check the colors before using)


Transistor: Uses a small current to switch or amplify a much larger current.

Comes in many different packages but you can read the part number off the package (P2N2222AG in this kit) and find a datasheet online.

3 (Base, Collector, Emitter)

Plugging in the right way round (also a current limiting resistor is often needed on the base pin)


Servo: Takes a timed pulse and converts it into an angular position of the output shaft.

A plastic box with 3 wires coming out one side and a shaft with a plastic horn out the top.


The plug is not polarized so make sure it is plugged in the right way.


DC Motor: Spins when a current is passed through it.

This one is easy, it looks like a motor. Usually a cylinder with a shaft coming out of one end.


Using a transistor or relay that is rated for the size of motor you're using.


Piezo: A pulse of current will cause it to click. A stream of pulses will cause it to emit a tone.

In this kit it comes in a little black barrel, but sometimes they are just a gold disk.


Difficult to misuse. 


Integrated Circuit (IC/"chip"): Packages any range of complicated electronics inside an easy to use package.

The part ID is written on the outside of the package (this sometimes requires a light or a magnifying glass to read)

2 to 100 (this kit has a TMP36 with 3 leads and a 74HC595 with 16 leads).

Proper orientation (check the mark, usually a half-moon, above pin 1.)


Push-button: Completes a circuit when it is pressed.

A little square with leads out the bottom and a button on the top.


These are almost square so they can be inserted 90 degrees off angle.


Potentiometer: Produces a variable resistance dependent on the angular position of the shaft.

They can be packaged in many different form factors, look for a dial to identify this part.


Accidentally buying logarithmic scale.


Light-Sensor: Produces a variable resistance dependent on the amount of incident light.

Usually a little disk with a clear top and a curvy line underneath.


Remember it needs to be in a voltage divider before it provides a useful input.


Relay: an electrically-controlled switch. 

Tall rectangle with pins underneath. Sizes range from small to very large (some relays even control train tracks!)

5 to 8 (automotive relays usually have 5 pins, the relay included in this kit has 8 pins)

Proper orientation. Check the marking on the relay, usually a small rectangle above the first two pins. The bottom of the relay sometimes has markings indicating coil location.


Produces a variable resistance dependant on the amount of infrared light.

Usually a small rectangle with a bump.


Make sure not to put it in backwards.


Emits infrared light when a small current is passed through it. (only in one direction)

Looks like a small light bulb.


Only works in one direction. 


Emits pulses of infrared light following the NEC Infrared Transmission Protocol.

Looks like a TV remote.


Difficult to misuse.

This guide was first published on Aug 18, 2017. It was last updated on Jun 12, 2017.

This page (Electronics Primer) was last updated on Jul 05, 2017.

Text editor powered by tinymce.