HX711 strange behaviour between channel A and B

Hi,

I am testig the HX711 Sparkfun Board (v11) and get some strange results. I use an esp32-s3-wroom-1u Dev baord to communicate with the hx711. I have no Loadcells connected, just the digital interface and Vdd = 3.3V and Vcc = 5.0 V.

I use channel A with GAIN = 64.

When I the hx711 is powered-up channel A reads around 5000 and drifts over 15-20 sec until it reaches somewhat about -500 to -1000. Then it stays there more or less. Sometimes it starts around 8000 and runs down to -2000. Then, after some minutes it suddenly drops down to 400, is stable for some time, and then drifts again to -2000…

When I connect a floating cable on 1 or 2 pins of channel B and start the system, channel A reads directly values around 450 and is stable. No changes after 10-20 minutes.

Has anyone an explanation for that behaviour?

I also tested to short channel B+ to channel B- with a jumper, but I got the same problem. Then I tried to short channel B+ to channel B- with a cable and the Problem is gone.

The problem also exists when I change the channels. So I read channel B and have a floating cable on channel A, everything is fine. I test without the cable and there is the problem again.

What is happening there? I am really really confused…What influence has channel B on channel A?

I hope somebody can guide me in the right direction…

Best

Jonathan

The HX711 inputs are designed to be connected to load cells or other low impedance bridge type sensors.

When the inputs are “floating”, the voltage values read are expected to drift, and are usually meaningless.