Resistor Color Expert
Resistor Color Expert

Resistor Color Expert



If you want to build something using a Raspberry Pi, you'll probably use resistors. Like the previous Resistor Color Duo and Resistor Color Trio exercises, you will be translating resistor color bands to human-readable labels.

  • Each resistor has a resistance value.
  • Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read. To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
  • Each band acts as a digit of a number. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.


In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take 1, 4, or 5 colors as input, and outputs the correct value, in ohms. The color bands are encoded as follows:

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

In resistor-color trio you decoded the first three colors. For instance: orange-orange-brown translated to the main value 330. In this exercise you will need to add tolerance to the mix. Tolerance is the maximum amount that a value can be above or below the main value. For example, if the last band is green, the maximum tolerance will be ±0.5%.

The tolerance band will have one of these values:

  • Grey - 0.05%
  • Violet - 0.1%
  • Blue - 0.25%
  • Green - 0.5%
  • Brown - 1%
  • Red - 2%
  • Gold - 5%
  • Silver - 10%

The four-band resistor is built up like this:

Band_1 Band_2 Band_3 band_4
Value_1 Value_2 Multiplier Tolerance


  • orange-orange-brown-green would be 330 ohms with a ±0.5% tolerance.
  • orange-orange-red-grey would be 3300 ohms with ±0.05% tolerance.

The difference between a four and five-band resistor is that the five-band resistor has an extra band to indicate a more precise value.

Band_1 Band_2 Band_3 Band_4 band_5
Value_1 Value_2 Value_3 Multiplier Tolerance


  • orange-orange-orange-black-green would be 333 ohms with a ±0.5% tolerance.
  • orange-red-orange-blue-violet would be 323M ohms with a ±0.10 tolerance.

There are also one band resistors. One band resistors only have the color black with a value of 0.

This exercise is about translating the resistor band colors into a label:

"... ohms ...%"

So an input of "orange", "orange", "black, green" should return:

"33 ohms ±0.5%"

When there are more than a thousand ohms, we say "kiloohms". That's similar to saying "kilometer" for 1000 meters, and "kilograms" for 1000 grams.

So an input of "orange", "orange", "orange", grey should return:

"33 kiloohms ±0.05%"

When there are more than a million ohms, we say "megaohms".

So an input of "orange", "orange", "orange", "red" should return:

"33 megaohms ±2%"

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