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UV Exposure Unit

In order to make your own PCBs (Printed Circuit Boards) you must have an UV-Exposure Unit since the boards are covered with a fotosensitive film to UV(Ultraviolett) light. So the circuit can be created with some Software-Tools like Eagle or ExpressSCH. Then the circuit will be printed on transparent paper (e.g. laser printer) and the than exposed to UV-light for a couple of minutes. Finally the board can be etched.

My motivation to do the UV Exposure Unit was to design, develop and etch my own PCBs. So I made a small wood box (380×240×145mm) and on the bottom I fixed a holes PCB with 143 UV LEDs. The anods and cathods are solded together.

I did't use pre-resistors LEDs since I used the 3.3V output of a power supply of uATX. The power supply produces enough current for all LEDs ~143*20mA = 2.86A. To controll the exposure time I made a small count down timer with an Atmega8 microcontroller and tree 7 segments displays to show the counted seconds. Here you can see how it works:

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