I needed a soldering lamp that didn't cast strong shadows and was an opportunity to salvage the LEDs from a broken TV left by the dumpster.
There are lots of ways to make a good soldering lamp from LEDs. I happened to pick a difficult path that required some reverse engineering but I hope you'll find the journey... illuminating. ;-)
9 Flexible LED strips (5 LEDs each)
- pulled from a broken TV
- also pulled from the same broken TV
DC power supply
- 30V block pulled from a broken printer
- pulled from a box of unused computer cables
3D printed frame
- Technically new, but I don't count 3D prints if they displace buying other plastic
Misc: rubber bands, tape, epoxy
- Technically new, but even the epoxy was a leftover from another project
Salvage percentage 100%! A useful tool made from 100% junk?! Cool!
It really comes down to two things:
- It needs to be bright. Stupefyingly bright.
- It needs to not cast deep shadows.
But these two things are often at odds. To get a bright light without casting deep shadows you need a distributed light (like a ring light). You could do this with lots of small laps, but that's a pain to setup and requires lots of plug space. And if you're like me, plug space is hard to come by in the places like a patio or garage where I like to set up a soldering station.
Brightness was the easy part. Just have lots of LEDs. Getting distributed light required flexing the LED strips into an arc and covering them with a diffusion layer (more on that later). In the images below you can see the 3D printed frame I used to hold the LED strips in a flexed position. None of the parts are glued together, instead the strips themselves exert pressure on the frame, locking the pieces in a friction fit.
Below, you can see small black pegs protruding through (pre existing) holes in the LED strips. A rubber band is woven over between the pegs to prevent the strips from popping out of the frame. Since rubber bands degrade over time, this is a temporary measure until epoxy can be applied to hold the strips in place in a more permanent fashion.
You may have noticed the LED strips alternate in length and LED placement. This is because the original strips in the TV were actually comprised of and "A" strip and a "B" strip. The way it was originally wired, the strips were combined in series as "AB", and then those were combined in series either 2 or 3 times and driven by a very high voltage (90V+). Since I didn't want a voltage that high in my light, I opted to split the strips and run them all in parallel. One problem with this approach was the "A" strips had 5 LEDs, but the "B" strips had 6. In order to run them all at the same voltage, I added a solder blob to bridge the contacts on one of the LEDs on the "B" strips to make them electrically equivalent to the "A" strips.
Using a home-made adjustable power supply (writeup coming soon), I was able to determine that a single strip of LEDs could be safely driven at full brightness by a 30V power supply. As it happened, I had a high current, 30V power supply on hand from a broken printer, so I simply soldered the wire leads to the exposed pads and covered them in hot glue for insulation and mechanical reinforcement.
I now had I bright, curved light that didn't cast deep shadows, but it was painful to use because the individual LEDs were searingly bright. Even mounted above a workstation, it was unpleasant to have the lamp in my peripheral vision. To combat this, I took the flexible diffusion layers from the TV but discovered they were only effective when they were at least an inch from the light source. To achieve this, I cut the diffusion layers into strips and tapped them in curved segments to the LED strips. Again, tape wouldn't last forever, so when I accidentally mixed too much epoxy on another project, I took the opportunity to reinforce the diffusion layer attachment points.
While certainly not the prettiest DIY project, it's been a invaluable tool in my workshop. And since the unfinished basement that has become my workshop isn't winning any design competitions, it fits right in. For anyone looking to do a first project without a microcontroller, LED lighting is a great place to start!