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Resistor Color Code Calculator

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Edit in the Resistor Color Code Calculator MicroSim Using the p5.js Editor

About This MicroSim

Real resistors are too small to print numbers on, so they use colored bands instead. This MicroSim lets you pick the color of each of the four bands and instantly see what value that resistor would have.

A horizontal resistor is drawn across the top of the screen. Below it are four columns of radio buttons — one column for each band — with every color choice visible at once and a matching color swatch next to each name.

  • Band 1 sets the first digit.
  • Band 2 sets the second digit.
  • Band 3 is the multiplier — how many times to multiply the two digits (a power of ten).
  • Band 4 is the tolerance — how far the real value may be from the printed value.

As you change any band, the resistor picture and the value update right away. The value is shown three ways so the units feel familiar: a short form like 1 kΩ, the full name 1 kilo-ohm, and the plain number 1,000 ohms.

How to Use

  1. Look at the resistor at the top. The default colors are Brown – Black – Red – Gold.
  2. Read the value below the resistor: 1 kΩ = 1 kilo-ohm = 1,000 ohms, ±5% tolerance.
  3. Try changing Band 1 to Red. The first digit becomes 2, so the value jumps.
  4. Change Band 3 (the multiplier) from Red to Orange and watch the value grow by a factor of ten — small numbers turn into kilo-ohms, big ones into mega-ohms.
  5. Try to build a 220 Ω resistor (Red – Red – Brown) and a 4.7 kΩ resistor (Yellow – Violet – Red).

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

Lesson Plan

Grade Level

Grades 5-12. The primary audience is curious beginners around age 10.

Duration

10-15 minutes

Prerequisites

  • Knows that resistance is measured in ohms (Ω).
  • Has seen the resistor color code table in Chapter 5.
  • Understands place value (ones, tens) and multiplying by powers of ten.

Learning Objective

Students can apply the resistor color code to read the value of a four-band resistor and express that value in ohms, kilo-ohms, or mega-ohms.

Activities

  1. Exploration (5 min): Let students freely change bands and watch the value. Ask: "Which band makes the biggest change to the value? Why?" (The multiplier band.)
  2. Guided Practice (5 min): Call out values — 330 Ω, 1 kΩ, 10 kΩ, 1 MΩ — and have students set the bands to match.
  3. Assessment (5 min): Show a photo or drawing of a real resistor and ask students to predict its value before checking it in the MicroSim.

Assessment

  • Can the student name what each of the four bands controls?
  • Given three band colors, can the student calculate the resistance before using the tool?
  • Can the student convert between ohms, kilo-ohms, and mega-ohms correctly?

References

  1. Resistor Color Code — Chapter 5: Electronics Fundamentals
  2. Electronic Color Code — Wikipedia