The procedure is as follows:

A] Parts needed 1. One LED torch, which uses 3 AAA or 2 AAA batteries, i.e either 3 or 4.5 volts, the 4.5 volts one preferred. I got mine LED circuit from old LED lights, LED emergency lights which I bought at my sunday market for Rs.15/- these lights are chinese made and give bright light...2.One usb extension cable, see if u have a spare at home, comes with any USB device, Pen Drive, Bluetooth Dongle, etc etc, u wud need to destroy the cable to make the light....3. Soldering IRon, Insulation Tape, wire stripper....


B} in USB cable keep the end of cable which is as shown in pix 1 and this pic as intact, remove the connector which is to the other side of cable, You would see 4 wires comming out of it. RED, BLACK, GREEN and WHITE.. Strip the RED and BLACK Wires and keep the GREEN AnD WHITE wires as it is .....


C] Connect the RED wire to the + ve of the LED circuit, and BLACK wire to the - ve of the CIRCUIT.. insulate the wires, or solder as per ur convence,,, Connect as shown in the picture... When connected to the circuit plug the other end of the USB connector into USB port of any computer...

D] AND VOILA see the LED s light up,, in my circuit out of the 6 leds only 4 LED worked still the light was very very bright, total cost of this experiemtn for me was 0 rs. as I already had the equipments..

E} Basic concept is the USB can give out power upto 5 volt, so if u plan to connect only one LED, which u can get from market for rs.2 or rs.3 ,, then use a suitable resistor as the 5 volt would fry the single LED

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One LED can sustain only 0.7 volt as after that the junction gets breakdown though it can run at 1v also but its life will be reduced.So i think to prevent need of resistor you can use 5 - 6 LED...
Or use a potentiometer.
Anyways nice trick though.Its the topic of my interest.
Rep+

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Very Nice Trick.Worked for me.Sorry Must Spread Some Rep Around.

cool i tried it and worked thanks