This lights an LED from a dead battery
One transistor and a hand wound coil that light a white LED from a nearly dead 1V cell. Six parts.
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
6 parts on a perfboard 11 × 19 holes, plus hookup wire.
| Qty | Part | Where to buy |
|---|---|---|
| 1 | Electrolytic Cap47uF C1 | Buy Electrolytic Cap on Amazon |
| 1 | Power Input (2-pin) J1 | |
| 1 | LED LED1 | Buy LED on Amazon |
| 1 | NPN Transistor (TO-92) Q1 | Buy NPN Transistor (TO-92) on Amazon |
| 1 | Resistor (axial)1k R1 | Buy Resistor (axial) on Amazon |
| 1 | Toroid Coil (centre tap) U1 |
Check every pin against the datasheet of the exact part in your hands before wiring.
As an Amazon Associate I earn from qualifying purchases.
Cut list
9 wires, 195 mm (7.7 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 | BlackVBAT D5 → F8 | D5 → F8 | 23mm | 13mm (90°) |
| 5 | BlueVBAT D3 → I3 | D3 → I3 | 23mm | Straight |
| 4 | GreenSWITCH I13 → G16 | I13 → G16 | 23mm | 10mm (90°) |
| 1 | RedBASE D17 → E15 | D17 → E15 | 18mm | 10mm (90°) |
| 7 | RedGND E5 → H5 | E5 → H5 | 18mm | Straight |
| 9 | WhiteGND H15 → G14 | H15 → G14 | 14mm | Straight |
| 3 | WhiteSWITCH H9 → H14 | H9 → H14 | 23mm | Straight |
| 2 | YellowFEEDBACK D13 → D9 | D13 → D9 | 20mm | Straight |
| 8 | YellowGND J5 → J15 | J5 → J15 | 35mm | Straight |
About this build
A Joule thief: one NPN transistor, a 1k base resistor and a hand wound centre tapped coil that oscillate at tens of kilohertz. Each time the transistor lets go, the coil stacks about 2V on top of a tired 1V cell, which is enough to light a white LED that a fresh cell alone couldn't.
The parts library has no toroid, so the video draws the coil footprint in the app first. Wind the two wires together, then join the end of one to the start of the other at the tap. Get that backwards and the feedback is backwards too, and it won't start.
Six parts on an 11 by 19 perfboard.
More builds
See all builds
VideoOne knob dims a 12V LED strip. No code.
One knob dims a 12V LED strip. A 555 timer makes the PWM and a MOSFET switches the strip. No microcontroller, no code.
12 parts · 22 wires
LightsPower
Premieres Nov 25The emergency light that turns on when the power dies
Three white LEDs that switch on from a battery the moment the wall adapter loses power, and charge it while it's plugged in.
14 parts · 5 wires
LightsPower
VideoThe Stranger Things light wall, from two chips
Six coloured LEDs light one at a time in a loop, like the Christmas light wall in Stranger Things. A 555 timer and a counter.
13 parts · 28 wires
LightsTimers and logic