RE: General calculation type question

Assuming your keypad is connected as follows:

1 2 3

A + + +

B + + +

1,2,3,A,B are all I/O pins on the PIC. Tie A and B high with resistor. Keep A and B with an output of '0'. In your program, output a '1' on A. Read pins 1 then 2 then 3 and see which one has a '0' value. This is the button that is pressed on A. If no button (or '0' on a pin) then your program puts A back to '0', sets B to '0' and scans 1 then 2 then 3 again looking for a '0'.

Normally I wouldn't recommend this exact circuit because one input is directly sourcing another. But because of the low duty cycle and the fact that a PIC can sink a couple of TTL loads, this has worked for me on a number of occassions.

Don't forget to allow some delays in your program for "key bounce".

John

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Darren King
Sent: Thursday, February 03, 2000 7:48 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: How to read 2 inputs connected together?

I know this is probably going to be a dumb question, but I haven't been able to successfully read inputs from a keypad. They keybad works by connecting 2 inputs TOGETHER when a key is pressed on 6 pins. I know how to read a pin when its pulled high through a resister out to V+ and if its low V-. But if they connect together what am I supposed to do to read this state?

Anyhelp thanks.

Darren King