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| UV LED Exposure Unit |
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| raynerd:
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. My brother-in-law did a great job of the box but I just need to replace the front control panel as the wood split early on in the build but being impatient I wanted to take the box and fit the components to see it it works. Now it does, I`ll give it him back and he said he`ll sort out a neater front pannel this weekend, mount the LCD properly and I`ll get some better momentry buttons and mount them on the panel as well. 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? |
| spuddevans:
That's a very smart piece of kit Chris :clap: :clap: :clap: :clap: :clap: :clap: Well done that man!! Tim |
| Stilldrillin:
That`s a great piece of work Chris, between you and brother in law! :clap: Could you explain what it does? :scratch: David D |
| andyf:
--- Quote from: Stilldrillin on March 20, 2010, 04:28:25 AM ---That`s a great piece of work Chris, between you and brother in law! Could you explain what it does? :scratch: --- End quote --- It's to save money, isn't it? No more need to visit expensive tanning studios :lol: :lol: Andy |
| raynerd:
David, you take a piece of copper clad board with a photosensitive etch resistant layer: You then print out the artwork on which your final network tracks are black and print it onto clear acetate transparency. Although I have heard you can print it onto paper and it will still work. Alternatively you can use a perminant marker and just draw on your tracks You then place the accetate on the glass surface of the exposure unit, put the copper pcb cladding on top, close the lid and expose with UV. The UV breaks down the etch resist in all areas other than those covered by black ink or marker. Therefore you end up with etch-resist still ontop of your tracks. You then place it in sodium hydroxide which is the developer and I believe is stripping the exposed etch resist completely from the board. You don`t leave it in too long or it starts to remove the etch resist from the tracks too. At this point you can now see your layout: The darker areas still have etch resist on them. The lighter areas are exposed copper. You then need to get rid of the exposed copper by etching it away with acid. I tried using HCl but it didn`t work too well so I went to using what most seem to use, FeCl3. Your then left with your board ready to drill and use: That is all in theory - I have only been through the process once! Chris |
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