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in my circuit i have - 16f872
pin 1 = 0,5 to 4 v
pin 2 = 0,5 to 4 v
pin 3 = 0,5 to 4 v
pin 4 = 0,5 to 4 v
pin 5 = 0,5 to 4 v
pin 6 = 0,5 to 4 v
pin 7 = 0,5 to 4 v
then i press 1 and 4,
pin 1 = 0v
pin 4 = 0v
obs: 0,5 to 4 is variant not estable
0 v = estable
i use this circuit for read one keypad, but i can't
because 0,5 = 0 then keypress all time
can i help me?
It is not possible to read this voltages by a digital input.
You have to use a lot of analog-inputs or design another keyboard !
i use 16f872 and adc input A0, ...
I use 4 pin for test 2 row and 2 col,
if i read with 4 pins....i'll be change the pic 16f877 or other 40píns
I'm not sure what your input is, are you saying with no key pressed you have between 0,5 and 4 volts, but with key pressed you get a solid 0V?
If so, then you need to use the analog to digital input feature. Unfortunately, the 16f872 only has 5 such inputs, and you need 7 inputs.