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Old 23rd Mar 2020, 7:29 pm   #331
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 4,078
Default Re: MK14 schematic revisions

Yes, the more variations, the merrier.

The basic principle (as originally suggested by fellow forum member TonyDuell) is to use pairs of optocouplers to join keypad rows and columns together to electronically 'press' the keys. The attached diagram #1 illustrates it from the optocoupler output point of view. You activate one row opto and one column opto together, and that presses the corresponding key.

You can easily find 12 outputs to drive the leds of these optos individually (+1, if you want the interface to be able to reset the MK14) on an UNO. The main problem I was anticipating was how to create a big enough serial receive buffer for the incoming Intel Hex file on the UNO. I didn't really solve that problem in the short time I spent thinking about it.
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