Monday, December 23, 2013

scanner: sealing/ hall effect sensor

I worked on sealing the scanner case yesterday. Cherise came in to wire the hall effect sensors that I had purchased to use in conjunction with the Rasberry Pi.  The hall effect sensors would trigger (aka:"switch") the scan button and the power to the scanner. The hall effect sensors work by using the magnetic field to trigger the switch. I had been reading about people building diving lights from mag-light flashlights and came across the boards above. It seems standard push button switches can be depressed from the pressures of deep water diving. I was hoping we could find a way to trigger a switch inside the scanner box, and yet not have to have anything protruding into the box to enable it. I found the boards above and watched the video where the maker of the boards triggers the switch through 1/2" aluminum. This looked perfect and I had hoped that these boards might solve our problem. I ordered the boards at the beginning of the week and had them by Friday.

Come Sunday afternoon, Cherise was having a lot of trouble getting the boards to work and there was discussion on changing the design out to a standard button. I was reluctant to drill yet another hole in the box to install a button that had the potential of either being depressed due to pressure or having the potential of a severe leak. Cherise called Nathaniel and he came in to look the circuit over. Cherise had thought that we possibly needed a transistor, and she and Nathaniel finally determined that they needed a relay. After many tests and looking over the circuit many times, they finally got everything right and the hall effect boards worked like a charm. The magnet could be waved over the hall effect board and the Rasberry Pi would then send the signal to the scanner to scan at 300 dpi. I had ordered extra boards so we could control the scanner power with a toggle hall effect board and even possibly make a 600 dpi button as well. After doing some tests with just the one hall effect hooked to the Pi, and having some trouble with the scanner needing a reboot, Cherise and Nathaniel decided that they would wire the other toggle hall effect board to control scanner power. I was happy to see that as I had been envisioning this all along and thought this would be a really great way to have total control of the scanner while under water. We got everything working properly and then we were ready to seal the case.

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