I've been looking for an opportunity to carry out an LED torch conversion for a while, but the criteria for finding a 'donor' torch were fairly stringent. It needed to be:
- capable of powering white LEDs (so containing a power source generating over 3.6V)
- actually, very inexpensive (in case I made a catastrophic error during the build and broke it)
The benefits of an LED torch over an incandescent one are simple - with the 'high brightness' 20 candle-power white LEDs it's now possible to buy on eBay (I bought fifty for 9GBP), a great deal of light can be produced, and significantly less current is drawn, so the batteries last a lot longer.
I was really pleased, therefore, to find a donor torch in a shop called 'Poundland' for just one UK pound (hence the name!) - it takes three D cells, which generates 4.5V - plenty to drive an array of LEDs.
Here's a list of things that are needed for the project:
- a cheap 4.5V 3xD cell torch (eg. from Poundland)
- 3 1.5V (so not rechargeable!) D cells.
- a 13x13 piece of 0.1" pitch copper-clad stripboard (like "Veroboard")
- 25 high brightness white LEDs (like these: http://is.gd/2Gaa0
- eBay link)
- 25 47ohm 0.25watt resistors (or whatever's appropriate - there's a handy parallel array calculator here: http://led.linear1.org/led.wiz
into which you can type the specifications of the LEDs you buy to get the correct value)
- 8cm of small insulated wire
- plastic packing ribbon
- resin adhesive (two-part if available)
- insulating tape
- blu-tak or equivalent (it's not a proper project if it doesn't involve blu-tak!)
- a couple of small screws
- a soldering iron and solder
- a drill or bradawl
- needle-nose pliers for bending
- a craft knife
- a hacksaw to trim the board down.