To be honest, this was suppose to be the first step to an EE workshop setup 'ible, but it came out so cool - I had no patience to not publish it immediately. This said, there will be more instructables on acquiring/making electronic tools in the near future.

What we have: an old desklamp made in USSR sometime around my birthyear.

What we want: bright and energy efficient lamp to use while soldering, tinkering, working, reading etc.

What we need:

- old lamp (free)

- 3-5W LED ($1.60-$1.80)

- ~9V 500mA power supply (got mine from the pile in the attic)

- LM317T linear voltage regulator ($1.50-$1.80)

- IRF540N mosfet or something capable of handling 300+mA ($1.80)

- 20KOhm and 2KOhm trim pots ($0.20 each)

- Pair of 10uF electrolytic capacitors ($0.10?)

TOTAL BUDGET: ~$6.00 or less

What we use:

- Soldering iron

- Wire cutters or your GF's/wife's nail clippers :{

- Small flathead screwdriver

- Multimeter

- Steady hands and nerves of steel

Step 1: LED Driver

The reason I didn't go with an aftermarket LED driver is that I have a pair of nice 5W LEDs with an unusual ratings: supply voltage is 6-8V with up to 700mA current (it has 2x2 SMD LED matrix). Forward voltage at which LED triggered was ~5.8V, this meant I could not use my pile of cheap 5V 1A buck converters to simplify the task.

So I could either go with a 10W driver, which would cost me more than a brand new LED desklamp, or make my own!

Above is a schematic of a simple driver. LM317T controls the output voltage, while IRF540 sets the load current.

Both voltage and current can be adjusted with potentiometers.

I know, this is not the most elegant solution and does not provide accurate control, but I had to make something capable of wide range of V/I values, since I did not have at that point the exact specs for these LEDs (those were free too). Plus it can handle loads of up to 1.5A.

I've also added a video with a preliminary test of my driver. Multimeter shows current @6.2V. As you can see this little guy glows very bright at only 15% of its max power.

You can assemble the circuit on a prototyping board, but I recommend making a PCB for any permanent project. The final driver assembly was about 35x15x20mm.

After a few blinding experiments I've decided to stop on 7.5V 300mA, which provided comfortable amount of light, while staying cool.

NOTE: LM317T or any linear voltage regulator of this class requires proper cooling if it's power dissipation is more than 1W. I've used a copper RAM heatsink, but there are cheap aftermarket aluminium ones with a mounting hole for TO-220 transistors.

Step 2: Putting Everything Together

This is a straightforward process, which starts with taking out all the insides of your lamp and replacing them with new components.

To prevent LED from bouncing around I've decided to mount it on a damaged mini-CD. It also serves as a nice reflector (see picture above).

Hook up the input and output wires to your driver. You can either cut the jack from your 9V power supply and connect it directly, or insert a matching female plug on a short wire to make your life easier in the long run.

If you decide to hook up an ON/OFF button, you can do it at either end (Vin or Vout), since this circuit only consumes only around 3mA at standby.

Thank you for your attention and see ya next time!

Check out my other projects and stuff in development at mygeekblog.net

P.S. I've been using this lamp for 4 days now and, holy cow, it makes soldering so much easier.

Next up: DIY prototyping stand.