In this instructable I will show you how I made a simple and expandable UV LED exposure unit. Exposure unit is a necessity for anyone who wants to make PCBs with the Photographic method. It will allow you to make high quality PCBs in no time. This is project is a great for beginners because of it's simplicity.
WARNING: Never look directly at UV light as it might damage your eyes.
Step 1: Photographic Method of Making PCBs
I did not make this video.
If you are not familiar with this method you can find out about it in the video above.
Although he said you can use a CFL bulb for exposing, you might not get as consistent and fast results as with LEDs. Nevertheless I encourage anyone to find out which method works for them.
Step 2: Parts List
For one small exposure unit you will need:
1x - step up DC-DC converter such as this XL6009 boost converter
1x - 12V-32V wall adapter
60x or more - UV LEDs - I recommend the flat top ones because they have beam angle of 120°. That means you can space them farther from each other so you don't need as many of them. Don't buy exactly the amount you need because some of them might not work.
6x - 150 Ω resistor
4x - M3 screw 6mm long
2x - M3 screw 10mm long
6x - M3 nut
4x - long M3 male standoff/spacer or you could use anything that does the job(long screw etc.)
Step 3: Schematic
The exposure unit is a very simple device that consists of just a power supply and LEDs with current limiting resistors.
The voltage drop of an UV LED is in the range of 3.2 V to 3.8 V and if we put 10 of them in series that means we need a power supply capable of outputting up to 38V. Although it turned out that the voltage drop of my LEDs was a bit lower so 31V was enough for me. But you never know what LEDs you will get. Therefore I recommend to set the voltage of the converter lower and instead measure the total current drawn by the module. The LEDs are rated for 20mA continuous current but I've found out that their brightness at 5mA is enough for me. It should also increase their lifecycle if we run them on lower current.
So start with the lowest voltage set on the boost converter and increase it until your ammeter is showing 5 mA x 6 rows = 30mA.
Once the boost converter's voltage is set you can remove the ammeter.
Step 4: Expand It
If you need to expose bigger PCBs you can build more of these modules and connect them together. Just make sure that their total current draw suits the equation (5mA) x (number of rows) = total current. This bigger one draws 90mA.
Step 5: Conclusion
At first you will need to experiment with the time of exposure until you find the right one. Mine was 1 minute and 30 seconds.
Now you should know what an exposure unit is and how to make one.
If you manage to build one don't forget to post pictures of it in the comments. Good luck.