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Date:  8-7-2019
Number of Hours:  2.00
Manual Reference:  
Brief Description:  Fabricate PCB for Overhead Switch Panel

1400 - 1600

Today I fabricated a printed circuit board for the overhead switch panel. This board will connect and support the three potentiometers. The board greatly simplified the wiring and will improve reliability.

To create the board, I used Express PCB, a free program available online, The pots were spaced for the panel and a schematic was created. The wiring is actually fairly simple; One trace provides a +5V reference voltage to all three pots. The next trace provides a ground to all three pots. Each of the three shorter traces provides an isolated wiper connection to each pot.

Once the schematic was drawn and checked, I duplicated the drawing in order to make three boards at once. This will give me extra boards if I run into a problem and it doesn't require any more time to etch three or just one. I printed two mirrored copies of the boards on transparency film. This became an issue as most new printers do not support transparency printing. I used a brother MFC7820 to accomplish the task. Two copies were printed to provide a perfectly opaque mask to use. The two prints were cropped and placed on top of each other. This closes any open pixels in the mask.

The prints were then taped to the inside of a picture frame glass. The frame provides an even clamping force to keep the prints flat on the board. I then went to a dark room and unwrapped the pre sensitized Datak board. This board is a Positive board; the traces are masked and the open areas are exposed to light. The board was placed with the photo sensitive side against the glossy side of the schematic print, taped in place and the back was then installed in the picture frame.

The next step was to expose the board to light. I previously set up a 150w bulb in a fixture placed 12" above the counter surface. The picture frame was placed under this light source for 13 minutes. After the time elapsed, the board was removed from the frame and place into a shallow dish full of Datak Developer. The solution was agitated until a
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