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Resistor Color Code Calculator

Run the Resistor Color Code Calculator MicroSim fullscreen

About This MicroSim

A club kit arrives with a bag of resistors and no labels. The value is written on each one in coloured stripes, and reading those stripes is a skill a mentor needs before the first session, not during it.

Set the four bands and the resistor above updates with its value in ohms, its readable name, and its tolerance. The structure is worth naming out loud: the first two bands are digits, the third is a multiplier, and the fourth is tolerance. Once a student sees that the third band is not a digit, the whole code stops looking arbitrary.

The value that matters most in a beginners' kit is 220 ohms -- red, red, brown -- the standard series resistor for an LED. Set it once and the group has a reference they can find in the bag by sight.

How to Use

  • Band 1 and Band 2 set the first and second digits.
  • Band 3 sets the multiplier -- the number of zeros, not a digit.
  • Band 4 sets the tolerance, how far the real part may be from its stated value.
  • The resistor drawing and the value above it update as you change any band.

Lesson Plan

Bloom level: Apply (L3) -- calculate

Learning objective: Given a resistor's coloured bands, the learner calculates its resistance value using the standard colour code.

Before the sim (5 min). Hold up two resistors that look almost identical and ask which one belongs in the LED circuit. Nobody can say. Then read the stripes.

With the sim (10 min). Build 220 ohms together -- red, red, brown -- and then 1 kilo-ohm. Ask what changed. Only the third band moved, which is the moment the multiplier idea lands.

After the sim (15 min). Hand out real resistors from the club kit. Each student reads theirs, predicts the value, then checks it in the sim. Finish by sorting the bag into labelled envelopes -- the sim just paid for itself in session-prep time.

Check for understanding. Give the colours brown-black-red and ask for the value before anyone touches the sim. The answer is 1 kilo-ohm, and getting there means the digit/multiplier split is understood.

Embedding This MicroSim

Paste this into any page of the book, adjusting the relative path to docs/sims/ for the page's depth:

<iframe src="../../sims/resistor-color-code-calculator/main.html" width="100%" height="542" scrolling="no"></iframe>

Specification

The full specification below is extracted from Chapter 16: Physical Computing and Electrical Safety Basics.

Type: microsim
**sim-id:** resistor-color-code-calculator<br/>
**Library:** p5.js<br/>
**Status:** Reused<br/>
**Source:** https://dmccreary.github.io/learning-micropython/sims/resistor-color-code-calculator/<br/>
**Source Repo:** https://github.com/dmccreary/learning-micropython/tree/main/docs/sims/resistor-color-code-calculator

Reused from the MicroSim catalog (WHAT match score 0.81). Learning objective: Given a resistor's colored bands, the learner calculates its resistance value using the standard color-code table (Apply).

References

Credits

This MicroSim is adapted from resistor-color-code-calculator in the learning-micropython project by the same author (source). It is used here unchanged; the club context is supplied by the lesson plan above.