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Topic: How to wire 24 buttons using only 13 wires? (Read 238 times) previous topic - next topic

ProjectVR46

My oven uses a 24 button dome switch panel, connected to the board with 13 pins.

My switch panel does not work anymore - seems that most/all of the wire tracers are corroded. I may be able to visually trace some of the wires, but not all.

Can someone point me to a schematic or some other document that shows how wiring 24 switches to only 13 pins is possible?


This will give me an idea if using an arduino between a homemade panel and the oven board is feasible.

Thanks!

DrAzzy

#1
Feb 11, 2019, 11:34 pm Last Edit: Feb 11, 2019, 11:37 pm by DrAzzy
It's done using a switch matrix. Google that and you'll get diagrams; there's an Arduino library to easily interface with a switch matrix.

24 buttons only needs 10 wires (6x4 or 5x5). Likely the other 3 are for two LEDs (1 common and one each for the LEDs), or possibly two non-matrix'ed buttons, or one non-matrix button and one LED. Sometimes dedicated switches are used for, say, a power button or something.

You'll need to trace out how the old panel was wired to know how to wire your replacement.

Also, diodes are needed (one per switch) if you need it to correctly interpret the case when two buttons are pressed at once (you probably don't in the case of oven controls?)
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jackthom41

You can also try shift registers like 74HC165 and can control all these inputs via 3 pins of arduino. Although you have to do some soldering for interfacing this shift register with arduino.
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Smajdalf

I think the problem is the oven expects specific wires to go to specific buttons. I think it will be better to try to trace as many wires as possible to get some idea how it worked. Try to post photos - someone may know it or have similar.
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ProjectVR46

I googled Switch Matrix, and that makes perfect sense! And I guess I won't be needing an Arduino after all, just a bunch of switches.

If I can't properly trace the wires I'll post a photo for help, or trace as many as I can then use trial and error for the rest. I can see how the display screen responds when I press a button and then just label the button accordingly.

Thanks to everyone for your help!

dougp

I think the problem is the oven expects specific wires to go to specific buttons. I think it will be better to try to trace as many wires as possible to get some idea how it worked. Try to post photos - someone may know it or have similar.
Or, there is a small possibility that it's a series of voltage divider circuits.  I just took a keyboard out of a boom box and the fifteen switches are wired as two voltage dividers.  Just sayin'.
Everything we call real is made of things that cannot be regarded as real.  If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet. - Niels Bohr

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Paul__B

I just took a keyboard out of a boom box and the fifteen switches are wired as two voltage dividers.  Just sayin'.
And that is what markedly limits their lifetime.

Contamination of the switch lubricant - or contact surfaces - over time causes spurious contact "closures" or mis-reads - "ciphers" and it becomes unserviceable.

dougp

Contamination of the switch lubricant - or contact surfaces - over time causes spurious contact "closures" or mis-reads - "ciphers" and it becomes unserviceable.
Yes, since a voltage divider necessitates analog sensing it'd be easy for a given switch to shift out of its R range.  This one though, didn't make it that far.  It won't even power up.
Everything we call real is made of things that cannot be regarded as real.  If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet. - Niels Bohr

No private consultations undertaken!

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