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I want to build a circuit that scans my 4x4 keypad using a binary counter and a '138 to generate the row scan and then read the results with a '374 which is read by the processor. The counter is clocked with a 555 timer. The counter will have to reset after it reaches 3. The resistors are pull-down. What would I use as a counter? A '161? And how would I generate an interrupt for the processor? Also wondering if there's some way to incorporate a debounce.