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Keypad with 3 pin hall effect sensor

ramussons

Jun 10, 2014
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You can try using an Opto Coupler to replace the mechanical switches in the 3x4 array. The Opto could be triggered by the Hall Sensor output.
 

Oe-

Jun 20, 2017
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So, I would wire each sensor to an opto and wire the optos in a matrix like i would on a standard keypad?

I've always wanted to get into working with arduinos and I thought making a small keyboard would be a cool start. Then I got those sensors for cheap and thought that would be fun but I ran out of pins. I looked into multiplexing but it seems like you can only press one key at a time which isn't very ideal.

I'll read up on the opto couplers more and see if I can use them. Thanks a lot for your suggestion.
 

Oe-

Jun 20, 2017
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If I understand this right, each opto needs an led to turn it on? What if instead I just wire the output using diodes. 1 for each column and row. Would that work?
 

ramussons

Jun 10, 2014
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So, I would wire each sensor to an opto and wire the optos in a matrix like i would on a standard keypad?

Yes

If I understand this right, each opto needs an led to turn it on

Yes. The Hall Sensor cannot drive the Opto's. You will need to interface a CMOS Buffer to drive the OPTO's.

What if instead I just wire the output using diodes. 1 for each column and row. Would that work?

Can we have a schematic of what you propose?
 

Oe-

Jun 20, 2017
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Please excuse the poor drawing, I didn't have graph paper. The 4 orange boxes are the sensors. I have 2 diodes on each output. The sensor should send a signal on the column diode and the row diode, but no other column or row should be affected since they are all on diodes.
20170629_142842.jpg
 

ramussons

Jun 10, 2014
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Is that a Keyboard Matrix Decoder on the Top Right?

My Understanding is that the "ROW" voltage is reduced and the "COLOUMN" voltage is increased when a Key is Pressed (or the other way ). I don't think the "Diode" setup will work.

Circuit_Encoder21.png
 

Oe-

Jun 20, 2017
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The box in the upper right is supposed to be a teensy. Which I could use to decode the matrix. And it looks like you are right, one seems to be pulled low and the other high. Back to the drawing board I guess. Thanks for the help.
 

ramussons

Jun 10, 2014
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Are you keen on a 3x4 matrix setup?
Why not a Decimal to BCD encoder?

encoder-and-decoder-8-728.jpg
 
Last edited:

Oe-

Jun 20, 2017
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The 3x4 isn't a must, only using it so I have enough pins on the teensy. The decimal to bcd encoder looks interesting. Never heard of that before so I'll have to look into it. Thanks
 

ramussons

Jun 10, 2014
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MosFET's Source-Drain conduct both ways. You 3x4 Matrix should be workable replacing the switches by the MosFET.
 
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