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I am trying to connect a button to my raspberry pi 3 (model B). I want to do it via the sysfs approach. Here is a picture or my small circuit: Picture of the circuit

It cannot be simpler: the black wire is connected to a GROUND pin and to the breadboard. The white wire is connected to pin GPIO 2 and a 1K ohm resistance is attached to it. According to https://fr.pinout.xyz/pinout/pin3_gpio2#, this pin features a 1.8k Ohm pull-up resistance.

Now, because I am not using Raspbian but a Debian buster compiled for raspberry, the GPIO pin numbers are offset by 458 (see https://wiki.debian.org/RaspberryPi3).

I export the pin and set it as input:

echo '460' > /sys/class/gpio/export
echo 'in' > /sys/class/gpio/gpio460/direction

Now I read the value:

cat /sys/class/gpio/gpio460/value

This outputs '1', and this is normal since this pin is pulled-up by default.

My problem is the following: when I close the circuit, this still reads '1'. Can you explain this behaviour?

When using another pin as output, I can controll a LED so this does not come from the strange gpio pin numbering of this OS.

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    It's often said that a picture is worth a thousand words, but you may have found the exception! :) Ground is pin 6, not GPIO3 (pin 5). See raspberrypi-spy.co.uk/2012/06/…
    – Edward
    Dec 29, 2018 at 15:34
  • Oops yes thanks, I corrected my post (but I indeed used physical pin 6 as ground).
    – Gru-gru
    Dec 29, 2018 at 16:28

1 Answer 1

Reset to default
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I think I know what went wrong. I did the same circuit as the one pictured in Mosmas' post here, except that I used a 1k resistor. It divided the voltage too much and so the pin was not reading a clear 0. I changed to a 300 Ohm resistor and it works now. Also, as Gordon points out in the same thread, I could also remove this resistor entirely, if I'm not afraid of accidentally creating a shot-circuit.

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