Author Topic: UV LED Exposure Unit  (Read 8333 times)

Offline raynerd

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UV LED Exposure Unit
« on: March 19, 2010, 07:09:22 PM »
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?










« Last Edit: March 19, 2010, 07:12:03 PM by craynerd »
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Offline spuddevans

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Re: UV LED Exposure Unit
« Reply #1 on: March 20, 2010, 03:36:26 AM »
That's a very smart piece of kit Chris  :clap: :clap: :clap: :clap: :clap: :clap:

Well done that man!!


Tim
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Offline Stilldrillin

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Re: UV LED Exposure Unit
« Reply #2 on: March 20, 2010, 04:28:25 AM »
That`s a great piece of work Chris, between you and brother in law!  :clap:

Could you explain what it does?  :scratch:

David D
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Offline andyf

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Re: UV LED Exposure Unit
« Reply #3 on: March 20, 2010, 05:11:40 AM »
That`s a great piece of work Chris, between you and brother in law!  
Could you explain what it does?  :scratch:

It's to save money, isn't it? No more need to visit expensive tanning studios  :lol: :lol:

Andy

« Last Edit: March 20, 2010, 10:01:21 AM by andyf »
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I've cut the end off it twice, but it's still too short

Offline raynerd

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Re: UV LED Exposure Unit
« Reply #4 on: March 20, 2010, 05:22:47 AM »
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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Offline BigBore

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Re: UV LED Exposure Unit
« Reply #5 on: March 20, 2010, 05:27:26 AM »
That's pretty slick! I like it.   :thumbup:

Ed

Offline Stilldrillin

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Re: UV LED Exposure Unit
« Reply #6 on: March 20, 2010, 09:45:59 AM »
Gotcher! ........ Now.......  ::)

That`s a bit clever, innit?  :thumbup:

I only understand things that rotate & move about a bit.....

Thanks Chris!

David D
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Offline raynerd

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Re: UV LED Exposure Unit
« Reply #7 on: March 20, 2010, 03:13:00 PM »
Well that is more than I understand !!

Second attempt just now... certainly not perfect but I think I need to improve the contrast of my artwork for that but I think this would be useable!

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Offline Brass_Machine

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Re: UV LED Exposure Unit
« Reply #8 on: March 21, 2010, 06:53:31 PM »
That's pretty neat Chris. The video I saw on doing photosensitive boards... the guy printed 2 of the particular board he was doing and lined them up one on top of another to help make sure everything that's supposed to be black, was. look for my link to the video. It may help you a bit.

Eric
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Offline raynerd

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Re: UV LED Exposure Unit
« Reply #9 on: March 25, 2010, 04:51:53 AM »
Eric, thanks for the reply. I didn`t see this until now when I have just come to update and that method would work really well. A much better idea than going over with a fine sharpy like I am currently doing. I know some people put it through the printer twice however when I try that it moves a fraction and just looks aweful! I will try that next time for sure... I watched the video and it was very helpful but that little tip imparticular was good.

I had an interesting evening last night. I gave this another go but using my own art work for a simple binary dice that I designed a few months ago when I was just getting to grips with EasyPIC6, Microcontrollers and Mikro C. It is only simple, you press a button and it gives you a 'random' number between 1 to 6, displaying it in binary. It also has a simple circuit so with little effort I could make it on a one sided PCB layer with no jumpers. I really need to learn how to use the polygon tool to make a ground mask but I couldn`t get it to work and was despirate to give the pcb making process a try...another 'something' for next time.

This was the design. I`m sure it could be a better layout. I started off during the last week learning how to use CADsofts EAGLE but I found it a real PITA. I must have clearly been using it incorrectly but I found the schematic layout fine but actual laying traces seemed so rigid, I just couldn`t get it to do what I wanted it to! I then tried the free version of Proteus, - Proteus Lite and it was excellent. It only took me a few hours and I had nearly designed my board:

I then printed it off, exposed my copper board it for 3 minutes in my UV box, developed for 1 minute and started etching:


Then to the part I had feared. I actually thought I was going to leave it there as I didn`t have a drill that could run at 5000rpm or great. I came across this which had been given to me at a shop clearance, it came in a little box with tiny drill bits and I knew the guy who owned it made pcbs as he had a UV exposure unit (didn`t know what that was at the time!). It says 10.5v on the front so I plugged it in DC 10v and expected it to fly around it went quite slow, relative to what I was expecting and certainly not 5k RPM!! Anyway, I couldn`t go any further as I had no drill stand, then I realized it was small enough to clamp in my milling machine. With little effort a 0.8mm drill bit went straight though and was very accurate. I experienced no snapped drill bits or wandering holes. The only issue was that the drill had very very little torque and consequently grabbed twice and got stuck so I had to twist it off.


Here is the board with components soldered. You don`t get a peak at the back side now as my soldering has a little to be desired!

It got late when I had finished and need to re-programme the PIC with the correct port for the button and then should give it a test. I may have done something wrong on the board design but the concept of making a PCB at home has worked! Next time I need stronger tracks but as I  mentioned above, I think doubling up the artwork transparency will help a great deal as there are currently clear areas of the track that are not sharp enough. Practice I guess..
Chris


 
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Offline ksor

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Re: UV LED Exposure Unit
« Reply #10 on: March 26, 2010, 12:09:53 PM »
Oh ... nice work !

What kind of UV LEDs did you use ?
Best regards
KSor, Denmark
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Offline raynerd

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Re: UV LED Exposure Unit
« Reply #11 on: March 26, 2010, 05:36:20 PM »
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