HX711 saturating

Hello all,

I am using a HX711 transducer (green board) with gauge sensor FX1901-0001-0200-L and FX1901-0001-0100-L from digikey (respectively 50kg and 100kg). I tryed with 2 of each above in case some would be defective (-> same result, see after).

What I experienced is that it is very linear, so "no" problem with programming, electronic and software : in a way it works.
The problem is that, whatever this sensor (50/100kg) it is saturating at something like half of its capacity. I tried to move to 32 gain on B way -> it helps to go a little higher but still saturating far from maximum load. I have calculated, considering our expection and experience that gain should be about 4 or something like that. Notice that in our mechanics there is no mechanical stop that could explain the problem.

So my question is : what went wrong ? how to set a lower gain ? what about adding a resistance between A- and GND to artificially reduce the gain ?

Thanks

Any idea would be appreciated
Emmanuel

Did you look at the load cell datasheet and notice that these load cells have a nominal 20 mV/V sensitivity (and the 0200 version has a nominal 36 mV/V sensitivity)? Since the HX711 excitation is about 4.3 volts, that means the load cells will output a differential voltage of 86 mV (or 155 mV) at full scale.

If you look at the HX711 datasheet, you will notice that the maximum permissible input differential voltage is approximately 20 mV (at the default 128 gain), 40 mV (at 64 gain), or 80 mV (at 32 gain).

You should be able to get near full scale with the 0100 version at 32 gain, but no where near full scale for the 0200.

Incorrect calibration may also contribute to your problem for both load cells.

Ok thank you for the explanation. What do you think if I add a resistance between the hx711 and measure gauge pin in order to lower output voltage : I do not need accuracy for my measurement (10% scale step is ok)
thank you

Impossible to tell if you have done it right if you don't post a connection diagram and code.

The crude way of dropping sensitivity is to add a 1k resistor between A+ and A-
Leo..

Thank you Wawa.
I'll try monday those and keep informed for anyone to know in the future

I confirm taht a resistor between A+ and A- drops sensitivity. I put a 1Kohm => perfect
Thank you all