Keypad with 3 pin hall effect sensor

[Oe-]

So I'm looking to make a key pad with hall effect sensors and I'm having trouble understanding how it could be done. My hall effect sensor has only 3 pins. Vcc, gnd, and output. How can I wire the outputs to make a 3x4 matrix?

https://www.digikey.com/product-detail/en/diodes-incorporated/AH1807-P-B/AH1807-P-B-ND/3829348

That's the sensor in question

 

[ramussons]

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-]

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-]

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]

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-]

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.

Spoiler: Picture

 

[ramussons]

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.

 

[Oe-]

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]

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

 

[Oe-]

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]

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