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Keypad Interfacing Problems

 
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Keypad Interfacing Problems
PostPosted: Mon Jul 20, 2009 12:47 pm     Reply with quote

I am interfacing a 4x4 matrix keypad with a PIC through the keypad encoder MM74C922. The problem I have is that some keys, when pressed multiple times, would give me different values, and there also seems to be a bouncing issue. I have put a 0.1uF capacitor across the osc pin and 1uF capacitor across the keybounce mask pin on the encoder. I have no idea why this is happening. Please help!
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Mon Jul 20, 2009 1:02 pm     Reply with quote

Read the comments in this article about safety and multple inputs:
http://www.geocities.com/dariuskrail20/LCDPad.html

If that doesn't help, then post a short, compilable, test program that
shows the problem. Strip it down to a very small program.

Post a list of the connections between the PIC and the MM74C922.

Post your compiler version.
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PostPosted: Tue Jul 21, 2009 2:11 pm     Reply with quote

Before I extract that part of the code:

I tried not connecting the keypad, and instead, tested it by shorting row/column pins with a wire. This worked without giving me any of the switching-between-numbers or bouncing problems. On the other hand, I tried the keypad with a demo board I used last year and it doesn't seem to be defective.

Does this guarantee that the problem exists in the code?

The thing is that on the old demo board I used a pic16f877, and on this one I'm using a pic18f4523. And I used pretty much the same setup as well as similar code.
asmboy



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PostPosted: Tue Jul 21, 2009 2:41 pm     Reply with quote

if (similar!=same) result=nul;
PCM programmer



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PostPosted: Tue Jul 21, 2009 6:12 pm     Reply with quote

If you want help, you need to post a short, compilable test program
that shows the problem. Also post a list of connections between the
PIC and the keypad chip.
AFAS87
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PostPosted: Mon Feb 15, 2010 2:12 pm     Reply with quote

hi.... i have the same problem.
any one can help
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PostPosted: Tue Feb 16, 2010 7:51 am     Reply with quote

I've used the 74C922 for years (20+,yeesh time flies !)..without any problems. I do connect and test the DV (data valid) pin.
Jay
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