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I have several RasPIs set up with Ubuntu Server 18.04 64Bit. One freshly setup up RasPIs 3B+ and two 4Bs. On all I can run the following minimum script without any error messages:

#!/usr/bin/env python
from gpiozero import Button, LED
from signal import pause

def print_pin(button):
    print(str(button.pin.number))

button1 = Button(20)
led1 = LED(4)

led1.blink()
button1.when_pressed = print_pin

pause()

The LED blinks on all of the RasPIs, however the button just works on the RasPI 3B+, but on none of the 4Bs.

I can't get any button working on the 4Bs, however LEDs work just fine and on some of them I use I2C, which also works perfectly fine. What could be the problem here?

I'm using the following versions on all RasPIs:

Linux ubuntu 5.3.0-1030-raspi2 #32~18.04.2-Ubuntu
gpiozero==1.5.1
RPi.GPIO==0.6.5
python-rpi.gpio 0.6.5-1ubuntu0.18.04.1

Just for completeness: In addition the 3B+ and one of the 4Bs have the following GPIO library installed for I2C:

Adafruit-GPIO==1.0.4
4
  • Probably wrong wiring. We need clear photos showing the connections you have made on the Pi4B.
    – joan
    Aug 7 '20 at 9:24
  • Ubuntu implementations have limited support for Pi hardware. Expecting an 2 year OLD (obsolete) OS to support hardware that wasn't released when it was is wishful thinking at best. Even the latest Ubuntu (which only claims to be a server) has limited support.
    – Milliways
    Aug 7 '20 at 9:48
  • @joan I applied exactly the same wiring to all PIs. Since 3B+ and 4B have the same pinout it should either be wrong for all of them or for none.
    – MichelH
    Aug 7 '20 at 10:05
  • @Milliways I'm aware of this issue, however I have to run ROS Melodic on these PIs and Melodic is tied to Ubuntu 18.04. I've used Ubuntu Server 18.04 with ROS on a RasPI 4 very often before without any issues, but never used the GPIOs before with Ubuntu Server.
    – MichelH
    Aug 7 '20 at 10:10
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I believe the problem is really in the old OS (or probably rather: Old libs) in use. The Pi4 requires an update to the I/O library for the input pull-up resistor setting to work properly, which is likely used by the above Button class. Try a never version of Rpi.Gpio, when possible.

Alternatively, you could add an external pull-up resistor to your button pin (assuming the button closes to ground).

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