4*4 keypad and micro controller

[rahul95]

hi

i m doing my first electronic project using pic16f877a and keypad and lcd.my code works well.(when i press a button , that key will display on lcd) but i still dont understand how pic understand which key is pressed. is there interrupts involved with that procedure. ( in my code lcd at portB and and keypad at portd)

thanks

 

[prashanttyagi85]

i don't know the pic microcontroller
but i think that the logic behind it will be same as avr.
the main logic is that microcontroller use 4keys as input and other 4 keys as output.
it continuously scan the input port
which ever key will be pressed it will detact 1 at that input pin as all column pins are connected to vcc.
simple

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[OunaLypse]

The ports feed as input to the pic, the pic will test for all ports at high rate, normally a keypad will be 4 or 5 inputs, the pic uses the code btfss/btfsc depending on your configuration.... it basically works like a switch.

for detecting, the keypad uses the technique of rows and columns.

 

[prashanttyagi85]

dear all
for interfacing 4*4 keypad with avr microcontroller we required 8 pins of microcontroller.
can anybody tell me that is there any way to connect it using 2 or 3 pins (like as serial comm.)?

 

[ctownsend]

dear all
for interfacing 4*4 keypad with avr microcontroller we required 8 pins of microcontroller.
can anybody tell me that is there any way to connect it using 2 or 3 pins (like as serial comm.)?

search google for EDE1144 Keypad Encoder IC

 

[FoxyRick]

dear all
for interfacing 4*4 keypad with avr microcontroller we required 8 pins of microcontroller.
can anybody tell me that is there any way to connect it using 2 or 3 pins (like as serial comm.)?

You can read a keypad with just one ADC input. See Microchip's appnote on it, or search google for examples:

https://ww1.microchip.com/downloads/en/appnotes/00234a.pdf