Picture of Arduino-controlled UV LED PCB Exposure Box
Why make an exposure box?

Like many Arduino lovers, once I began creating larger projects I obviously did not want to keep them on a fragile breadboard.  As many people do, I started to assemble my projects on cheap prototype boards.  While these boards were fairly rugged, their layouts were confusing to say the least and were basically organized chaos! So I learned how to etch my own circuit boards.  While there are several ways to go about making your own boards, with the two most popular being toner transfer method or the photo-resist method .. I chose to go with photo-resist using pre-sensitized boards.  This involves designing your board in software such as Eagle CAD, printing your circuit out on transparency film with a laser printer, exposing and developing the board with a light source, and finally etching the board with ferric chloride solution.  My very first board came out perfect to my surprise but it was pure luck.  As I made more boards I quickly found out that I never achieved the same results twice.  What I found out is that the exposure time and the distance between the board and the light source must be EXACT every time.  I was over or under exposing my boards most of the time.  I wanted to make my own fool-proof exposure box that #1 would expose each and every board in the exact same way with evenly-distributed light and #2 precisely time the exposure of every board down to the second.  I also knew that using UV light would greatly reduce the required exposure time.

It was well worth the effort!  I found that the perfect exposure time for any board was only 2 minutes – 15 seconds for a 4x3 PCB, which is generally the maximum size of nearly all of my projects.  This exposure box is specifically made for 4x3 inch boards, but can be scaled up if your projects demand larger boards.

So in the end I simply print and cut out the 4x3 transparency film, lay the film glossy side down in the exposure window, peel and place my blank PCB into the window (which fits like a glove), enter my exposure time, press START and walk away!

And again keep in mind that I designed this box especially for 4 x 3 inch boards.  You can easily scale the project up or down by simply adjusting the window size AND the number of UV LED's used.  I would estimate 9 LED's for every square inch of copper.
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Dylon1241 year ago
Why don't you make a standalone arduino? It's much cheaper than a $10 arduino nano.
relic1974 (author)  Dylon1241 year ago
Good question! I sent a BOM to some suppliers. The quotes to make a simple atmega168AU clone was around $15. Can you suggest a cheaper way?

The Nanos do make for convienent 30 pin IC socket plugins tho :)
I'm busy designing a similar control board with an atmega328 minimum circuit as I have a few chips lying around. Makes reprogramming it a little more finicky without on-board USB, but it'll be the cheapest solution I can manage - less than £5 with the chip, socket, crystal and 2 caps. Might even go crazy and add a resistor and momentary switch for a reset button :)

I did my LED array on stripboard but I like the look of yours much better. I'll probably use mine to make one of yours
relic1974 (author)  Jon D1 year ago
Throw a UART on that bad boy, they're not much. 6 pins for an ISP header :)

I'd love to see your board when you are done. I used 850nm LED's, 2 minutes exposure time for a 4x3 board.
You're right it would probably be worth it just so I don't risk damaging pins on the atmega pulling it out and putting it back in again. Or risk putting it in the wrong way :)

Does your array get pretty warm when its been on for a minute or two? mine does and I'm thinking I might want to put a cooling fan and maybe a thermistor in to get some circulation, but if yours doesn't I'll leave it out
relic1974 (author)  Jon D1 year ago
No it doesn't get hot despite 63 LED's. But it's on a thick board of copper with a wide ground plane. You could use a 60W CFL bulb @ 12 inches away for about 8 minutes to expose the board array I supplied.
ASCAS1 year ago
Thanks for sharing! This should get featured :D