Electronic Components

Level: Beginner

I’m about to attend the first meet-up of a local Nodebots group, and I thought it would be a good time to brush up on some basics. If you’re new to building robots, then this should serve as a good start!

The research for this post comes from multiple sources, but particularly http://node-ardx.org and Wikipedia.

This isn’t meant to be an exhaustive list. These are just a few of the common components newcomers are faced with, and they can be tricky to work with, at first.

You can leave a comment here, or tweet me (@assertchris) if you spot errors or have some tips about these components.


Diodes are like a one-way valve, allowing current to flow in a single direction. Diodes are typically marked with a line indicating the side of the ground pin.

This pin (which goes towards ground) is referred to as an cathode. The other pin (which goes towards positive) is conversely referred to as a anode.


Resistors limit the flow of current. They vary in how much they limit the flow of current, which is conveyed in the form of coloured bands. The colours have different values:

  • (0) Black
  • (1) Brown
  • (2) Red
  • (3) Orange
  • (4) Yellow
  • (5) Green
  • (6) Blue
  • (7) Purple
  • (8) Grey
  • (9) White

One of the bands are a multiplier. This special band is a multiplier for the resistance conveyed by the preceding bands. These colours also have different values:

  • (0.01Ω) Silver
  • (0.1Ω) Gold
  • (1Ω) Black
  • (10Ω) Brown
  • (100Ω) Red
  • (1kΩ) Orange
  • (10kΩ) Yellow
  • (100kΩ) Green
  • (1mΩ) Blue
  • (10mΩ) Purple

One of the bands convey a tolerance. This special band shows how much the potential resistance can vary (usually due to manufacturing conditions). These colours also have different values:

  • (10%) Silver
  • (5%) Gold
  • (1%) Brown
  • (2%) Red
  • (0.5%) Green
  • (0.25%) Blue
  • (0.1%) Purple

Resistors typically have four to five bands. You can also find resistors with six bands, but they display a temperature tolerance we won’t talk about here.

Reading Resistors

Resistors can be tricky to read, at first. Here are a few steps you can take:

  1. The bands are always in the order; two (or three) digit bands, one multiplier band and one tolerance band.
  2. Reading from left to right; a resistor with red, red, black, black, gold would be 2, 2, 0, 1Ω, 5% (or between 209Ω and 231Ω).

The tolerance band is supposed to be thicker, but in practise this only happens if you’re lucky, or purchase high-quality components. You can usually tell the digit bands (and multiplier) apart because there’s a bigger gap between the multiplier and the tolerance band than between the first and second digit band.

This resistor has four bands, which means they are digit, digit, multiplier and tolerance. The values are 2, 2, 10Ω, 5% or (220Ω).

This resistor has five bands, which means they are digit, digit, digit, multiplier, tolerance. The values are 2, 2, 0, 1Ω, 5% (220Ω).

This resistor has four bands. 4, 7, 10Ω, 1% (470Ω).

Light-Emitting Diode (LED)

Light-Emitting Diodes (LED) are like mini, low-powered light bulbs. They have two (or sometimes more) pins, and as they are diodes, these pins allow current to travel in one direction only. This direction is indicated in two ways:

  1. The anode (or pin that goes towards positive) is longer.
  2. The cathode (or pin that goes to ground) is on the flat side of the “bulb”.
More often than not, you’ll need to use these in combination with resistors, or they will quickly burn out.


Transistors are simple, essential components of just about every electronic device today. In essence, a transistor allows one charge to control the flow of another. In other words; when one of the pins (the middle one) receives a charge, it allows a current to flow between the other two.

The pins of a transistor are commonly called base, collector and emitter. You can think of base as the switch which, when charged, allows current to flow from the collector to the emitter (in the direction of ground).

Transistors can be used as switches (current from collector to emitter is on/off) or amplifiers (the charge applied to base exponentially affects the current flowing between the collector and emitter, as a kind of resistance).

As with LEDs, you’ll usually want to use a current-limiting resistor on the base pin.

Transistors replaced vacuum tubes, for their size and low-price manufacture. They are also used in the implementation of logic gates.


Relays are like heavy-duty transistors, which act as electrically controlled, mechanical switches. Relays usually appear in the form of a box.

The number of pins depends on the kind of relay, but they are commonly used to join two of the pins (to complete a circuit), via electro-magnetism. Sometimes a click can be heard as the relay closes the circuit.

Electro-magnetism is when a current is run through a coil of wire, producing a magnetic force. This force diminishes shortly after the flow of current does.


Motors are mechanical devices capable of deriving motion through electro-magnetism as current is applied to a coil of wire contained in the chassis of the motor.

Motors draw far more current than LEDs (for example) and should be used in conjunction with a suitable transistor or relay. It’s not uncommon to connect multiple motors to a relay PCB, for devices involving Arduino, Raspberry Pi and motors.

Motors are also used in conjunction with diodes to prevent sudden voltage spikes being send back into controllers (like Arduino or Raspberry Pi). These diodes are commonly referred to as flyback diodes.


Servos are a form of motor which allow very accurate movement (by degrees). They usually contain a motor component and a sensor component (to determine the precise adjustments needed for angular granularity).

Servos take a timed pulse of current and translate it into the required angle. The motor then rotates the shaft until the sensor determines that the desired angle has been achieved.

There are two common types of servos; fixed range and continuous rotation servos. Fixed range servos can only move within a fixed range (e.g. 0° to 180°). Continuous rotation servos can rotate a full 360° and keep on going!

They usually have three pins; positive, ground and control.