Laptop Light Build Thread

[jqavins]

I'm taking a weeks long Teams class at work, with cameras on. As I face the camera, there's a window behind me. There's an LED next to the lens, but it's useless. So I'm making another light to clip or tape on.

First, I drew a pattern to make a slightly dished reflector. I attached the pattern to one side of a piece of cereal box and aluminum foil to the other side shiney side out, of course.


(Tje pattern is printed twice because I planned to make two and put them on the two top corners of the screen, but I seem to only have one white LED.)

I cut the outline and scored the interior lines, then folded and taped it into the final shape.

Then I cut a hole at the point just big enough to friction fit a white LED.


Next I breadboarded the driver. It's not the best way to dim an LED but it's the simplest pretty good way I know. It didn't work. I troubleshot it. I found the breadboard is bad; there's a break in one of the supply rail rows, and I don't mean the one that's supposed to be there. That left me a bit frustrated and it's bed time anyway.

I'll post the schematic tomorrow when I have time to draw it properly.

 

[jqavins]

Here's the schematic:

I'd like R to be 1K, but I only have 10K pots on hand. Will that provide enough base drive? Rough (mental) calculation says it will make the control decidedly non linear, but I don't know how badly to the naked eye. That's why I was breadboarding it, i.e. to see if I need to get a different pot.

If I get my hands on another LED (like ordering one) then I only need a second transistor and fixed resistor (I have plenty of those) and both drivers can be controlled by the same pot. That would make it all the more important to get R down. But then, if I'm ordering LEDs I can order pots at the same time. That's sounding more and more like a good idea.

To make this tangentially, slightly rocket related: you know those tiny cardboard tubes that certain igniters come in? The ones we keep because they might be good for something even though they are so small and thin walled? I'll be attaching one of those to the reflector as a stalk to tape to the laptop.

 

[jqavins]

So, back in April, I did have this working nicely on a white breadboard, then I soldered it up on a breadboard with solder pads but no traces, and I managed to mess it up. Then I got side tracked, then the classes were over, so I never finished it.

Well, I've got three more days of TEAMS class this week, and had a flurry of productivity over the weekend, so I now have it working, albeit still on the white board. I did add two fixed resistors around the pot.

R3 keeps the transistors' bases up to about 0.5 V minimum, so I don't waste a tenth of the pot's range in cutoff. R2 keeps the bases about 0.5 V below the rail in order to keep the transistors out of deep saturation; I don't know if that matters in this application, but it seemed like a good idea, and it can't hurt.


View attachment 20230717_130405.mp4