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Resistor Color Code Decoder

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About This MicroSim

Resistors are too small to print numbers on, so their value is painted on as colored bands. On a four-band resistor:

  • Band 1 and band 2 are digits (black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9).
  • Band 3 is the multiplier: how many zeros to add (black ×1, brown ×10, red ×100, orange ×1k, yellow ×10k, and so on; gold ×0.1 and silver ×0.01).
  • Band 4, set a little apart, is the tolerance: how close the real value is guaranteed to be (gold ±5%, silver ±10%, brown ±1%, red ±2%).

For example, orange-orange-brown-gold is 3, 3, then add one zero: 330 Ω ±5%, the most common resistor in this book.

Click any band to step through its colors and watch the value change. The two quiz modes turn the decoder into practice: read a random resistor, or set the bands to make a value.

How to Use

  • In Explore mode, click a band to cycle its color. The readout shows the value, the tolerance, and the arithmetic. Random resistor shows a new random resistor.
  • Choose Quiz: read the bands and press Random resistor. Type the value you read (for example 470, 4.7k, or 1M) in Your value and press Check (or Enter).
  • Choose Quiz: set the bands and press Random resistor. Click the bands until they match the value in the box, then press Check. You may also type your own value into the box and set the bands for it.
  • The Score counts correct answers out of answers checked. Changing the mode resets the score.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/clocks-and-watches/sims/resistor-color-decoder/main.html"
        height="422px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objectives

By the end of this activity, students will be able to:

  • Recall the digit value of each resistor band color.
  • Apply the color code to read the value of a four-band resistor.
  • Apply the color code in reverse to choose the bands for a given value.

Grade Level

9-12 (Clocks and Watches with AI)

Duration

10-15 minutes

Prerequisites

  • Read the Resistors section of Chapter 2.
  • Know that 1 kΩ = 1,000 Ω and 1 MΩ = 1,000,000 Ω.

Activities

  1. Decode the favorites (3 min): Students set the bands for 220 Ω, 330 Ω, 1 kΩ, and 10 kΩ, the resistors they will use most in this book.
  2. Read quiz (4 min): Students answer ten random resistors in "Quiz: read the bands" and record their score.
  3. Set quiz (4 min): Students answer five questions in "Quiz: set the bands." Ask: which band is the most common mistake?
  4. Real parts (4 min): If a resistor kit is available, students read three real resistors and check each one in Explore mode.

Assessment

  • Students score at least 8 out of 10 when reading random resistors.
  • Students can name the four bands for a given value such as 4.7 kΩ ±5% (yellow-violet-red-gold).
  • Students explain what the tolerance band means for a real 330 Ω ±5% resistor (between about 314 Ω and 347 Ω).

References

  1. Electronic color code (Wikipedia) - The full color code table for resistors.
  2. Resistor (Wikipedia) - What resistors do and how they are made.
  3. E series of preferred numbers (Wikipedia) - Why resistors come in values like 22, 33, and 47.
  4. Resistor Color Code (SparkFun) - A tutorial with photos of real resistors.