Author Topic: Making an analog hall effect keyboard  (Read 2071 times)

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Offline Faltim

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Making an analog hall effect keyboard
« on: Fri, 25 October 2019, 10:49:21 »
I am creating my own keyboard using magnets, mostly for fun. I've been thinking a lot about the wiring, and most of the designs I've come up with have some type of issue to them.

Analog hall effect sensors will be responsible for reading the magnetic field and outputting a value between 0 and 5 volts. My first idea was to have each matrix column connect to an analog multiplexer, so that 64 signals would become 8 signals that could then be read as rows by some micro-controller. The issue with this solution is that each hall element draws between 6 and 10 mA, and that times 64 is a lot of current for something like this.

So now I am working on the idea of powering each column after the other, much like a regular keyboard matrix, and then reading the output of each row from that powered column. This idea is much like one I read on this forum, on a post made by dorkvader. This means that I could also use libraries that exist already (except the whole analog read part.. ). Below is an image of my planned schema:

228855-0

What do you guys think? Is this idea solid or is there a better way of doing it? I know Steelseries has a new analog hall effect keyboard, and I am unsure how they solved it. Any tip would be greatly appreciated!

Offline equalunique

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Re: Making an analog hall effect keyboard
« Reply #1 on: Sat, 26 October 2019, 11:21:33 »
This is great. I don't know much about circuit design.

*BUMP*

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Offline Blitzschnitzel

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Re: Making an analog hall effect keyboard
« Reply #2 on: Sat, 26 October 2019, 17:51:41 »
Well, if you power the sensors from the matrix and multiplex them wouldn't they just draw 8 x 10mA at a time?
Maybe keep all hall effect sensors constantly powered and put an optocoupler or something behind Vout. Then you could build a key matrix from the optocouplers.

228907-0

Not tested Or completely thought through! :D
« Last Edit: Sat, 26 October 2019, 18:01:46 by Blitzschnitzel »

Offline Findecanor

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Re: Making an analog hall effect keyboard
« Reply #3 on: Sat, 26 October 2019, 20:26:30 »
Cool!

BTW, Input.Club is launching a hall effect switch and keyboard series that is supposed to be analogue. It is about to have entered production. They have promised that once it has shipped (est: Feb 2020), their design will become available as open source. The MCU is Microchip ATSAM4S. The rest is not known yet.
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Offline Faltim

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Re: Making an analog hall effect keyboard
« Reply #4 on: Sun, 27 October 2019, 02:48:28 »
Well, if you power the sensors from the matrix and multiplex them wouldn't they just draw 8 x 10mA at a time?
Maybe keep all hall effect sensors constantly powered and put an optocoupler or something behind Vout. Then you could build a key matrix from the optocouplers.

(Attachment Link)

Not tested Or completely thought through! :D

Yeah the whole idea with the multiplexers was to power all hall sensors at the same time, that's why the current would have been high. But if I were to power each column individually I would not have to worry about that, but then I would not need the multiplexers either!

Your solution looks interesting, but what would be the benefit of using optocouplers here instead of something like transistors? Except isolation of course. And as I mentioned, powering them all at the same time would draw up to 650mA as they are always operating.

And the hall sensors output an analog signal that I want to access, maybe that's another reason optocouplers would be smart?

Offline Faltim

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Re: Making an analog hall effect keyboard
« Reply #5 on: Sun, 27 October 2019, 02:51:20 »
Cool!

BTW, Input.Club is launching a hall effect switch and keyboard series that is supposed to be analogue. It is about to have entered production. They have promised that once it has shipped (est: Feb 2020), their design will become available as open source. The MCU is Microchip ATSAM4S. The rest is not known yet.

That's cool! Man I wish the design was out right now  ^-^