Tuesday, June 03, 2008

Weekend project - nightlight

It's a simple project, build a night-light because the bathroom lights are blown out and I am renting so not included to climb into the ceiling and DIY. The boys need a night-light to get to the bathroom with, so I normally leave just 1 globe on in there. I broke-up a 'power-saver' downlighter with about 50 leds in it, not a bad price for superbright leds which can cost 80p each; if you do not count all the time and fussing with broken glass, splinters, serious desoldering etc.
(above picture looks blue on account the camera, and the leds being on very dim)
OK Drilled holes 5mm into the enclosure, wire them up with 1KOhm dropper, but in a series parallel network - all connected to a dumped phone-charger wall-wart i found as the supply.
Next we drill a hole in the back of the enclosure to allow the ~12Vdc cable in, and epoxy the enclosure to the top of the wall-wart. Normally this would create a heating problem, but I'm in a cold country.Since it's proved the PSU is good enough for the light-output need (tested on Saturday night as a burn-in), we move to the automatic light sensor - all prototyped on the project-board. You can see how I decided on a double-decker circuit arrangement. I only did this because I have a mental disease, no other reason at all. Besides the easy way was too easy.

Finished assembly with transfer of components to the veroboard. Because the LDR is a very flimsy model, I soldered a paperclip into the board on one side, covered it in heatshrink, and bent it to make a kind of stand-off before soldering the other leg of the paperclip into the far side. It made a very strong handle to which I epoxied the LDR - you can just see the 'window' on the right at the bottom of the enclosure. Lastly to stop junk and anything poking into the enclosure I stuck a clear window into the box to cover the hole from inside.

One assembly trick I also like to use when moving stuff from project to vero is to use a IN4007 diode clamp or similar across everything - I find that the 1 in 10 times that you work on the circuit while live and inadvertently cross power wires it will save your (I assume you do not use a 10Amp PSU. LOL) semiconductors.

The prototyping; you can see the flimsy LDR sticking up on the left. Apart from junkbox, recycled and bulk-bought resistors the onlybits I paid for are the LDR, LM741 and the enclosure.
Want a diagram?

No comments: