Pocket LED Torch

A really simple LED torch can be made from a twin AAA battery holder, which already has a switch fitted. These can be purchased from eBay and other suppliers.

The voltage from the single 1.5v cell is boosted by a simple "joule thief" circuit, using a ZTX653 transistor, a 2k2 resistor and a ferrite bead with approximately 20 turns of enamelled copper wire bifilar wound (wound double) 0.15mm diameter (38 awg).

Remove the clip furthest from the switch, cut off the battery spring and drill a hole for the LED. Snip off the red wire close to the switch and solder it to the battery contact that you just cut in half then slot it back into the plastic housing.
There's room to fit 2 LEDs connected in series. (In fact the circuit will easily drive up to 6 LEDs connected in series.)

Ferrite Bead Order Code: FT01629
TUB4/2/5-3B1 - Ferrite Tube, Cylindrical


I built another with 5 LEDs. It has a rechargeable 1.2v cell (750 mAH capacity) and it will run continuously for over 11 hours, at which point the LEDs will flash on and off at about 5 Hz.

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