Reading Resistor Colour Codes

Learning Goals 5 min

By the end of this lesson you will be able to:

1. Read any 4-band resistor by starting from the tolerance band and decoding the colours into a number with units.
2. Use a multimeter set to ohms (Ω) to measure an actual resistor and compare the reading to its rated value.
3. From your kit, physically identify a 220 Ω, a 1 kΩ and a 10 kΩ resistor by colour alone — no multimeter peeking.

Warm-Up 10 min

Last lesson we used Ohm's Law to pick the right resistor for a 5 V circuit. Today we learn how to actually find that resistor in your kit — because every resistor looks the same at a glance.

Quick-fire puzzle

Aisyah opens her starter kit and tips out a bag of resistors. They all look like tiny beige tubes with coloured stripes. Without measuring anything:

1. How can two resistors that look almost identical have completely different values?
2. Why does the kit use coloured stripes instead of just printing the number on the side?
3. If a resistor has 4 stripes — red, red, brown, gold — which end do you start reading from?

New Concept 20 min

The big idea — a barcode for ohms

A 4-band resistor's stripes are a tiny barcode. Each colour stands for a digit. Read them in order and you get the resistance value in ohms.

What each band means

On a 4-band resistor, reading from the tolerance band inwards:

• Band 1 — first digit of the value
• Band 2 — second digit of the value
• Band 3 — the multiplier: how many zeros to add after the two digits
• Band 4 — tolerance: how accurate the resistor is (almost always gold = ±5% in your kit)

Anatomy of a resistor

The colour-to-digit chart

This is the chart you will use for the rest of the course. Keep it open in front of you.

A trick to remember the colour order

The first ten colours go in the order of the rainbow, with black at the start and grey/white at the end. A short Malay-and-English memory phrase used in workshops in KL:

"Big Bats Race On Yellow Ground, Blue Vans Go West."

Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey, White. Make up your own — the sillier, the better it sticks.

Recording a decoded value in a sketch

Just like the last lesson, we record each decoding as a comment in an Arduino sketch. The chip ignores comments — humans read them.

// Resistor decoding worksheet — Aisyah, Form 2
// Bands: red, red, brown, gold
// Digits: 2, 2  →  22
// Multiplier: brown = x10
// Value: 22 x 10 = 220 ohms  (±5% tolerance)

void setup() {
}

void loop() {
}

Why it matters

Every external component in this course needs the right resistor. Pick the wrong one and your LED is either invisible or fried. Reading the colour code is the very first habit of a good electronics builder — faster than reaching for a multimeter every single time.

Worked Example 20 min

Goal: decode three resistors from the starter kit and verify each with a multimeter.

Step 1 — orient the resistor

Pick up the first resistor. Turn it so the gold band is on the right. Now you are reading left to right.

Step 2 — read the first three bands

Suppose you see: brown, black, red, gap, gold.

• Band 1 — brown = 1
• Band 2 — black = 0
• Band 3 — red = multiplier ×100
• Band 4 — gold = ±5% tolerance

Step 3 — combine

• Digits: 10
• Value: 10 × 100 = 1 000 Ω = 1 kΩ

So that resistor is a 1 kΩ. The ±5% tolerance means a multimeter reading anywhere from 950 Ω to 1 050 Ω is normal and fine.

Step 4 — verify with a multimeter

1. Set the multimeter dial to the Ω (ohms) region. If it has ranges, pick 2 kΩ or 20 kΩ — anything bigger than the expected value.
2. Touch one probe to each leg of the resistor. Don't pinch the metal legs with your fingers — your body's resistance will throw the reading off.
3. Read the screen. Expect roughly the rated value, within ±5%.

Step 5 — decode two more and record everything in a sketch

Repeat for two more resistors. For each, write down the colours, the decoded value, and the multimeter reading.

// Three resistors decoded and measured — Aiman, Form 2
// 1) brown, black, red, gold     -> 10 x 100 = 1 000 ohm = 1 kohm
//    Multimeter reading: 0.98 kohm  -> within 5%, OK

// 2) red, red, brown, gold       -> 22 x 10 = 220 ohm
//    Multimeter reading: 218 ohm    -> within 5%, OK

// 3) brown, black, orange, gold  -> 10 x 1k = 10 000 ohm = 10 kohm
//    Multimeter reading: 9.91 kohm  -> within 5%, OK

void setup() {
}

void loop() {
}

What changed since last lesson? In L01-05 you calculated which resistor you needed. Today you can actually find that resistor on your bench in seconds — without measuring every one.

Try It Yourself 20 min

For each task, decode the bands on paper, then verify with a multimeter. Save your final notes as comments in a sketch named resistor-codes.

// Task: yellow, violet, brown, gold
// Digits: ____, ____  ->  ____
// Multiplier: brown = x____
// Value: ____ x ____ = ____ ohm
// Multimeter reading: ____ ohm

void setup() {
}

void loop() {
}

// Three mystery resistors from my kit
// A) bands: ____, ____, ____, gold  -> ____ ohm
// B) bands: ____, ____, ____, gold  -> ____ ohm
// C) bands: ____, ____, ____, gold  -> ____ ohm

void setup() {
}

void loop() {
}

// Task: find a 4.7 kohm resistor by its bands
// 4.7 kohm = 4 700 ohm = 47 x 100
// Band 1 (digit 4): ________
// Band 2 (digit 7): ________
// Band 3 (x100):    ________
// Band 4 (5%):      gold
// Multimeter reading: ____ ohm

void setup() {
}

void loop() {
}

Mini-Challenge 15 min

The kit-sorting sprint

Combine today's colour-code skill with the Ohm's Law thinking from ARD-L01-05. Working in pairs, sort your starter-kit resistors into four labelled groups using only your eyes — no multimeter — and prove which group is which.

Your task:

1. Tip out every resistor in your starter kit onto the desk.
2. On four slips of paper, write the four target values: 220 Ω, 560 Ω, 1 kΩ, 10 kΩ.
3. Sort each resistor onto the correct slip — using only the colour bands, in under five minutes.
4. For each pile, write the band colours you used to identify them and, using Ohm's Law from L01-05, calculate the current that would flow if the resistor was placed between 5V and GND.
5. Finally — and only at the end — check three random resistors with a multimeter. If any of your three is in the wrong pile, your sort fails.

It works if:

• Every resistor sits on the slip whose value matches its band colours.
• Each of the four piles has a written band sequence next to it that matches the chart in §3.
• Each pile shows the current it would let flow at 5 V — 22.7 mA, 8.9 mA, 5 mA, 0.5 mA — within a milliamp.
• None of the three random multimeter checks contradicts your sort.

Recap 5 min

A 4-band resistor's value is a colour barcode. Read from the tolerance band (gold) inwards: two digits, a multiplier, and the tolerance. Combine the digits, multiply, and you have the resistance in ohms — usually within ±5% of the printed value.

Resistor

A small component that limits how much current can flow. Measured in ohms (Ω). The kit holds 220 Ω, 560 Ω, 1 kΩ, 4.7 kΩ and 10 kΩ values.

Band

A coloured stripe painted around a resistor. 4-band resistors have two digit bands, one multiplier band and one tolerance band.

Multiplier

The third band's value, telling you how many times to multiply the two digits. Brown = ×10, red = ×100, orange = ×1 000.

Tolerance

How accurate the resistor's value is. Gold = ±5% — almost every resistor in your starter kit.

Multimeter

A handheld instrument that measures resistance, voltage and current. Set the dial to Ω to check a resistor.

Homework 5 min

Build your own resistor reference card. Open the Arduino IDE, create a sketch called resistor-reference, and write the following as comments above an empty setup() / loop():

1. The five resistor values stocked in your kit (220 Ω, 560 Ω, 1 kΩ, 4.7 kΩ, 10 kΩ) and their full 4-band colour patterns.
2. Pick two of those resistors. For each, use Ohm's Law (from L01-05) to calculate the current that would flow if the resistor was placed between 5V and GND. Show your working.
3. Decode this mystery resistor: orange, orange, red, gold. What is its value in ohms?

Bring back next class: the saved .ino file on a USB stick or a phone photo of the IDE window showing the reference card and answers.