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geekhack Projects => Making Stuff Together! => Topic started by: E3E on Thu, 19 November 2015, 23:42:45

Title: [HELP] Tip on matrices. Low resistance between two rows causing key press errors
Post by: E3E on Thu, 19 November 2015, 23:42:45

I have no idea what's up with this. I really need to learn more about keyboard matrices.

(http://puu.sh/lrWnG/3640997ec2.png)

When I check continuity between the two adjacent column (not row, whoops)  pins, the resistance is only 062-092 whereas all other columns are around 1600-1700 resistance.

So whenever the 8 key is pressed, the 5 key is activated and not the 8 key.

Whenever the I key is pressed, the T key is activated, not the I key.

Whenever the K key is pressed, the G key is activated, and so on.

I know this is probably super simple and I'm just being dumb, but I can't figure out what to do to fix it.

I should also say that this is on a Duck Eagle PCB. I added Holtite sockets to the board so I assume I mucked something up. I've done this to another Eagle PCB without issue, but it seems that this one has gotten caught on this one issue.

What could be causing the lack of resistance?

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I have also traced the pins back to the processor, and well, on the one with the problems, there's a resistance of 1500 or so at the first pin. This is from the column pin. The row pin seems like it's fine.

On the functional board, there is no resistance and a beep sounds from the multimeter. It seems like something could be causing a conflict somewhere.

Title: Re: [HELP] Tip on matrices. Low resistance between two rows causing key press errors
Post by: user 18 on Fri, 20 November 2015, 00:08:13

You have a short circuit somewhere. Check that you haven't accidentally bridged any connections with solder. If your board has a case made of a conductive material, you will also need to confirm that nothing with current running through it ever touches the case.

Title: Re: [HELP] Tip on matrices. Low resistance between two rows causing key press errors
Post by: E3E on Fri, 20 November 2015, 00:21:40

Quote from: user 18 on Fri, 20 November 2015, 00:08:13

You have a short circuit somewhere. Check that you haven't accidentally bridged any connections with solder. If your board has a case made of a conductive material, you will also need to confirm that nothing with current running through it ever touches the case.

Hey, user! That's exactly it, I pinned it down to some connections I had to fix thanks to the Holtite sockets requiring some widening of the pin positions. Tracked down the culprit!

Thanks though! I knew it had to be something like this, but I was starting to lose hope until your response gave me some additional determination. :D

Title: Re: [HELP] Tip on matrices. Low resistance between two rows causing key press errors
Post by: user 18 on Fri, 20 November 2015, 00:28:13

Not a problem, glad you got it figured out!