I currently have an Arduino UNO (running Wheatstone bridge example code from website via serial port) and a strain gauge shield (RB-Onl-38) on top.
I have a 5Kg load cell connected to Input 1 and it displays a changing load via serial monitor as expected - works fine !
The problem I have is on the other Input 2 where I have the input voltage (mV) from a wheatstone bridge (three 120ohm resistors and a 120 ohm strain gauge) that I have tested separately.
The output from the bridge is approximately 2mV (multimeter) when loaded. Unfortunately when this is fed into the middle two pins on shield Input 2 this isn’t amplified by 495 ! It doesn’t change at all…
I have checked excitation voltage on outer 2 pins and there is 3.3V and GND.
Can anyone suggest why a load cell works but a single strain gauge in a wheatstone bridge feeding into the shield doesn’t ???
]Did you try to connect your 5Kg load cell to the Strain 2 input to verify if the channel 2 works properly on the shield ?/:m] ]How do you power your Wheatstone birdge ? Are you using 3.3V and GND of the outer pins of the channel 2 connector or the Shield ? /:m]
•Did you try to connect your 5Kg load cell to the Strain 2 input to verify if the channel 2 works properly on the shield ?
Yes works fine.
•How do you power your Wheatstone birdge ? Are you using 3.3V and GND of the outer pins of the channel 2 connector or the Shield ?
Yes
I have also feed the wheatstone bridge circuit output into a breadboard op-amp circuit (INA125p) and it works !! so don’t know why the shield doesn’t ?
Could you post clear pictures showing your wiring ? What is the voltage output you have from the shield (on the A1 pin pin for Strain 2) when the strain gauge is not pressed and when it is pressed ?
We honestly didn’t test the RB-Onl-38 with a strain gauge in a Wheatstone bridge configuration. The RB-Onl-38 works with all sorts of Load Cells and in theory, should also work with a strain gauge in a Wheatstone bridge.
I’ve actually only got this image unfortunately because it was setup for a student project and now it is finished and we ended up using an INA125P opamp circuit instead to read the load.
I don’t have exact voltage figures but it was noted that there was a change of plus/minus 0.02V (2milli Volts) when deflecting the strain gauge and reading this on a multimeter. I would have assumed feeding this 2mV into the amplifier shield with a default gain of 495 would have provided a few volts deflection…or at least some difference in voltage but it didn’t.
