Driving a led segment and keypad?

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gamepi
 
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Driving a led segment and keypad?

Post by gamepi »

I am hacking an old TI-30 calculator. It wired up the positive voltage of the keypad and the LED matrix together. How can I read the voltage with a MAX7219 LED Driver and a 74HC595 shift register?

I know that the key presses on a calculator will be relatively long so I think that I could shut off the MAX7219(through arduino pin or transistor?) and pulse the matrix for keys, then repower the MAX7219 and resend it data.

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