Every LED needs this resistor. Here's the math
Three red LEDs on 5V, each behind a different resistor, so you can see how the resistor value sets the brightness.
Free build sheet
The parts, every wire with its length and bend points, a bend guide, both sides of the board and checkboxes to track your progress. Print it or keep it open at the bench.
Open the build sheetWhat you need
7 parts on a perfboard 16 × 28 holes, plus hookup wire.
| Qty | Part | Where to buy |
|---|---|---|
| 1 | Power Input (2-pin) J1 | |
| 3 | LED LED1, LED2, LED3 | Buy LED on Amazon |
| 1 | Resistor (axial)150 R1 | Buy Resistor (axial) on Amazon |
| 1 | Resistor (axial)330 R2 | Buy Resistor (axial) on Amazon |
| 1 | Resistor (axial)1k R3 | Buy Resistor (axial) on Amazon |
Check every pin against the datasheet of the exact part in your hands before wiring.
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Cut list
9 wires, 217 mm (8.5 in) in total, in the order the build sheet cuts them. Wire numbers match the build sheet. Each length includes 5 mm per end to go through the hole.
| Wire | Colour and net | Length | ||
|---|---|---|---|---|
| 6 | Black5V C9 → C5 | C9 → C5 | 20mm | Straight |
| 5 | Blue5V I10 → L10 | I10 → L10 | 18mm | Straight |
| 4 | Green5V D10 → G10 | D10 → G10 | 18mm | Straight |
| 1 | RedD1 C15 → C20 | C15 → C20 | 23mm | Straight |
| 7 | RedGND D5 → D22 | D5 → D22 | 53mm | Straight |
| 9 | WhiteGND I22 → L22 | I22 → L22 | 18mm | Straight |
| 3 | WhiteD3 M15 → M20 | M15 → M20 | 23mm | Straight |
| 2 | YellowD2 H15 → H20 | H15 → H20 | 23mm | Straight |
| 8 | YellowGND C23 → H23 | C23 → H23 | 23mm | Straight |
About this build
Three red LEDs sit on the same 5V rail, each behind a different series resistor: 150 ohm, 330 ohm and 1k. The brightness difference on the board is the math made visible.
One line picks the value every time. R equals the supply voltage minus the LED's forward voltage, divided by the current you want. That's why 150 ohm gives about 20mA, 330 ohm about 9mA and 1k about 3mA.
Leave the resistor out and nothing limits the current, so the LED doesn't last long.
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