Luis Bruno

All You Need

There’s an inherent dilemma in purchasing a flashlight: The really bright and long-lasting LED models are pretty expensive, and the heavy, cheap traditional ones always seem to be dead just when you need them the most. Good thing it’s possible to build your own superbright, reliable and inexpensive hybrid light.

With a bit of creative circuitry work—you’ll need to add a small circuit called a charge pump to increase the voltage—you can replace the bulb in any cheap lantern-style flashlight with several bright white LEDs. All you need to power your DIY version are three small AA batteries instead of that huge, heavy six-volt. Plus, LEDs will last far longer than regular flashlight bulbs, so you’ll never be left in the dark.

Turn the page for a parts list and step-by-step instructions.

Create A Powerful LED Flashlight

TIME: 2 HOURS | COST: $29.29
Easy | | | | | Hard


(1) Flashlight (Harbor Freight Tools #93858; $6.99)

(1) Rock Bottom Freeduino Kit Plus (Wulfden at Hawk’s Mountain; $12.50)

(8) White LED 10,000 mcd 3.3V (Mouser #859-LTW-2S3D7; $0.41)

(1) MOSFET 60V 200mA N-Channel (Mouser #863-2N7000RLRPG; $0.28)

(1) Schottky 1A 40V Rectifier (Mouser #833-1N5819-TP; $0.18)

(1) Ceramic capacitor 1µF 50V (Mouser #581-SR215E105MAR; $0.34)

(1) Electrolytic capacitor 22µF 25V (Mouser #647-UVR1E220MDD; $0.18)

(1) RF Choke 100µH (Mouser #542-5300-25-RC; $1.01)

(1) 3xAA battery holder (Mouser #12BH331-GR; $0.99)

(1) 2 ¾- x 6 1/16-inch perfboard (RadioShack #276-1395; $2.79)

(3) AA batteries (local purchase; $0.25)
Scrap wire


1. Assemble the Freeduino kit.

2. Disassemble the flashlight, remove the incandescent bulb, bulb holder, and reflector.

3. Cut two pieces of perfboard: one circular piece for fitting inside the flashlight’s reflector and another piece for holding the charge pump components. Solder the eight white LEDs in series on the circular perfboard. Assemble the charge pump circuit (see G. Y. Xu article in February 2008 issue of Nuts and Volts).

4. Download and burn our charge pump code onto the Freeduino. Connect the Freeduino (use pin D3) to the charge pump circuit. Connect the charge pump to the serial LED ring. Attach the LED perfboard to the inside of the flashlight reflector.

(Copy and paste the code on the following page for your Freeduino sketch.)

5. Attach the bulb holder to the reflector and solder the battery holder to the + and – contacts on the back of the bulb holder.

6. Install the three ‘AA’ batteries and slide the battery holder, Freeduino, and charge pump circuit inside the flashlight and thread the reflector/lens cover back in place.

7. Push the flashlight’s power button and test the circuit. It will take approximately 5-10 seconds for the LEDs to illuminate once power is applied to the circuit. Now you should be able to shed some light on your nocturnal automobile repair.

The code for your Freeduino sketch:

_/*  Charge Pump_
_**   13 June 2008_
_**   PopSci.com_
_**   Freeduino Pin_
_**   Pin D3 = output_

_// Freeduino Pin D3 for output_

**int** pumpPin = 3;

**void** setup() {

  **pinMode**(pumpPin, OUTPUT);


**void** loop() {

_// Set Pin D3 for full output_
  **digitalWrite**(pumpPin, HIGH);

_// Pause for 7 microseconds_

_// Turn Pin D3 OFF_
**digitalWrite**(pumpPin, LOW);