PCB UV LED Exposure Unit
I`ve been working on this for weeks now, much longer than hoped but I finally got my first PCB made earlier this evening. UV leds are from ebay – not much more than £8 of which half of that was postage for 200. The unit is running off my ATX PSU conversion that I posted about earlier. The LEDs are wired four in parallel with a small 10 ohm resistor on each string – forward voltage of an LED was just short of 4v so I had 1v to drop across the resistor. Current drawn by each LED is 30mA and so the 95 LEDs and the microcontroller circuit draw about a total of 3A. The microcontroller timer circuit uses a PIC16F887 programmed using MikroC and first developed on my EasyPIC6 board. There are still a couple of bugs in the code which I will also address this weekend, they should be fairly straight forward but I just wanted to trial the concept. I was at first attempting to use a 32khz watch crystal like I used on my binary clock but after some guidance from a friend I realised it was easier to use the internal osc, calculate the frequency of interupts and time “one second” from that. It is nothing like as accurate as 32khz xtal but then for timing a rough 4 minutes does it have to be?
Second attempt! Looks better and I think usable!