Reading bending strain in 2 directions with HX711 or Robotshop wheastone bridge amplifier shiels

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1

Hello,

I want to measure the strain of a bending beam in a battery supplied application. For this reason I am thinking of using HX711 or Robotshop wheatstone amplifier shield before connecting the bridge to my Nucleo F334R8 microprocessor .

I am thinking of using a half bridge configuration (thus 2 strain gages will be used in opossites sides of the beam)

half bridge
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My question is whether HX711 or Robotshop amplifier will be able to identify the direction of the bending (which gage is stretched and which is compressed) ?

From what I understand Wheatstone bridge output voltage will be positive in one case and negative in the second case, right ? If yes, how are HX711/ Robotshop shield able to measure the change in the sign of the voltage?
(Robotshop shield connects to analogin of the microprocessor which reads 0-3.3 V while HX711 connects to one digital pin and one pwm pin)


3

Hi,

The load cell shield provides a 0-3.3V analog signal on pin A0 (Strain 1) and pin A1 (Strain 2). Each channel has a reference voltage potentiometer (Ref1 and Ref2) that you can set to mid-supply and measure bending of the bridge in both directions. For example, you can set the analog signal output to 1.65V (or 512 in ADC raw value) when no force is applied on the bridge, therefore, you would have values > 1.65V when the bridge is bent in one direction and < 1.65V in the other direction. There is no negative voltage output from the load cell shield.
As for the HX711, it has a serial output interface and not an analog voltage signal. We invite you to take a look at the HX711 IC Datasheet.

1 Like
4

It makes sense. Thanks for the response.