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We have observed some strange behaviour on the serialless-pin (GPIO21 or pin 40 on the connector) in combination with PI4 and StromPi3.

The serialless option is not used and so we set this jumper to 'off'. Apart from that we have connected a buzzer to pin 40 which is controlled by the PI. Normally pin 40 is configured as an input and the pin is pulled low. If we want to sound the buzzer we configure the pin as output and drive it high. Afterwards the pin is configured as an input again. 

Sometimes however the pin is continuously driven high or low and we can't control it by means of the PI. So we wonder if it is possible StromPi3  is driving the pin? We verified we are notdriving the pin ourselves using utility pinctr. Its output is shown below.

Is it possible StromPi3 is causing this behaviour?

Hello JdV,

if you set the serialless jumper on the StromPi to OFF, the connection between StromPi and GPIO 21 is fully interrupted and you can use the pin freely.

Best regards 

Tim (Joy-IT)

Hi Tim, thanks for you response.

Oke, good to know StromPi cannot control the pin if the jumper is set to OFF.

Thanks!