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For an application I am currently developing, I need to be able to get the status of a button (pressed or not pressed) or a switch (which can be considered a button in some way).

While I could theoretically use regular GPIO for this, this will not be a viable solution as the amount of buttons may be up to 50, which would require 2-3 additional Pi's.

Googling around I stumbled upon this bus called 1-Wire. All the examples show tenperature logging, using a DS18B20 if I'm not mistaken, but the concept seemed to fit my use case as well. I figured if something "complex" (compared to a simple button or switch) as a temperature sensor exists for this bus, then surely a simple button or switch must exist too.

Yet I didn't manage to find anything so far, any clues?

  • Sounds like a keyboard. Are you using a Zero? HID emulation might work. – bobstro Sep 19 '17 at 0:15
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    Here is Maxims overview over their different 1-wire chips maximintegrated.com/en/pl_list.cfm/filter/21 – MatsK Sep 19 '17 at 3:18
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    Do you need to detect all buttons indenpendently? If not all kombinations of buttons are valid, think about building a key matrix. If you don't need fast reaction (1-wire would not allow that either!), multiplexing would be another option. – Philippos Sep 19 '17 at 8:47
  • @Philippos I thought about that but that would still require sqrt(amountbuttons) GPIO pins, which isn't optimal for further extension – Pieter De Clercq Sep 19 '17 at 13:05
  • @MatsK thanks alot, I found something that fitted my case! – Pieter De Clercq Sep 19 '17 at 13:07
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You can use a I2C GPIO expander to have more GPIO like this one or you can consider pin multiplexing.

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Problem solved; I used the link provided by @MatsK (https://www.maximintegrated.com/en/pl_list.cfm/filter/21), it lists several switches that fitted my case.

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Maxim make the DS2413 1-wire, only issue I have with the ones I've used is they are rigged as passive power, i.e. only 2 wires to the device (1-wire and Ground) Works great for short cable runs and up to about a dozen devices on the bus, which for me is fine I'm controlling relays to drive a bunch of temp sensors and fridges.

For a big distributed network you'd need to find a version that ran with the 1wire but powered to 5v, I never tried that with the ones I have.

I think 50 would probably overload a single 1wire bus, (I'm at 10 ok) so the i2C expander is probably a better option in the long run.

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