Making of the UV Oven

To start, I had to make the array permanent and to such dimensions so as to have even lighting all over the surface of a typical photo-resistive PCB. So I laid them as shown, taking into account the distance of the leds which was enough to have overlaping beams of all leds. (so no blind spots where created) .

This was put in a ikea FIRA box, slightly modded for the purpose. (I left only the bottom drawer, didnt put the mid panels and used one of the mid panels as a swing door, attached to the top of the box with safety belt ribbon, glued and stapled to the box and door)

The first test consisted of burning two photoresistive boards with components needed to make MIDIBOX sequencer v3.3 . It was a total success. as it can be clearly be seen.

Before going into burning the midibox sets , I performed some tests. The results were as such.

* With the current setup (35 UV leds (UV =395nm) at about 20mA each from a distance of around 30cm) the board needed around 15 minutes to be developed
* Reasonable results were between 10 and 20 minutes
* The film used was simple inkjet transparency but I would print it TWICE (my printer is accurate enough) or use two printed transparencies one on top of the other

They were then developed using the standard procedures (NaOH in water for removing excess photo resist and then FeCl3 or Sodium persulfate or whatever you are used to)

The results were AMAZING. The Oven was (and still is) one of the most important tools in my "lab". (The timer was dumped, I had a watch and pulled the plug)

PS. The array of leds needed quite a lot of current/voltage and I was lucky to find a hewlett-packard printer transformer with 1A/37V output.. Don't test THAT with your tongue!
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Joe said...

Nice, are all of the LEDs in series or parallel?

Aris said...

There is a parallel line of strings of serially placed leds. Which is actually this.. I connected 7 leds serially and did that 5 times. These strings are connected in parallel.

I did some small calculations based on the voltage drop of each led and the current I wanted each led to have so if you go to my files, there is an *.ods file (Open document spreadsheet, opens with openoffice) where you can put your values for the leds and transformer in your setup and it spits out the resistor you need to place so as not to burn the leds or not get light at all.

If you have any questions, please drop me a comment. !!!

Anonymous said...

Why not using another array of leds on the bottom of the cabinet? If you use a transparent pcb holder (maybe metacrilate of some other transparent plastic) you can get double sided boards! :)

Aris said...

There was only one time I ever wanted to make a double sided board and this was for the timer I designed for the UV Box. I just turned it over after 15 minutes :)

The thing is that these leds have a beam angle of 25 degrees so if the board gets too close to the leds, there will be circular spots where the exposure is greater. It might ruin your board this way.

Nevertheless, in a more demanding environment, your idea would be very time saving. It just cuts the exposure time in half.

Anonymous said...

RE: testing transformer with a tongue
power being 37watts (A times V), and assuming you are tranfering that every second it makes 37 joules. According to google 50 joules are lethal. Conclusion: testing that with your tonghe won't kill, but you would certainly feel the pinch

john said...

About how much time did this take you and about how much money would it cost (ignoring the cabinet) if I had to buy everything?

Aris said...

I got the leds of e-bay (50 leds for $10) and a perfboard from the local electronics shop for 3 euros ($4 but you can find cheaper on ebay). The transformer was salvaged from electronics recycling so it was free for me. I used a simple SPDT switch (add $1 at most but you can do without the switch). You might also need one resistor of high Wattage (2W resistor, no more than $0.30) and ribbon scraps or something to use as a hinge. so, it wouldn't cost more than $20 at most.

Stendall said...

You are goin to fry your leds.
Always, always, always there are tolerances.
It's not a good idea to put them in serial.

Aris said...

Hi Stendall,

The current and voltage going through the leds is exactly as calculated in the excel sheet.

(and no led has been fried up to now)

Thing is that I need to put the sheet back online because it seems it is lost from rapidshare. I will seek another way to have files to download because I have no personal hosting.

Any Ideas?