Hi everyone,
I am currently working on using the Arduino Mega board, HX711, and Wheatstone Bridge Circuit in order to obtain values of pure strain from a strain gauge connected to an aluminum pipe when a load is applied at one end , but I am kind of lost on how exactly to write the code. I have seen many projects using a load cell in order to output weight for a digital scale, but none that output values of strain directly found from the strain gauge in real time. I would like to obtain strain in the serial monitor in real time which will change with different weights being applied, and with a tear function to zero out the value if needed. Would anyone know how to write this code?
Please post an example of the code you have tried, using code tags, and explain how it differs from your expectations.
output values of strain directly found from the strain gauge
The resistance of a strain gauge sensor changes when under strain. The HX711 does not measure the resistance.
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I haven't developed much code yet because I honestly don't know where to begin becasue I am confused on how to relate the load cell projects to a single gauge, but the circuit schematic is as follows
Do you know how strain relates to weight?
I think you need to learn a bit more about how strain gauges work, so that you can better define the project. The setup you have is not great for estimating the resistance change of the strain gauge under load.
How that resistance changes with weight depends on the material and structure of the support to which the strain gauge is attached.
You can find instructional tutorials on line. First check the web pages produced by strain gauge manufacturers.
I have all the hand calculations completed in order to understand what strain values I should be obtaining at certain areas. For example, when I apply a 10 pound force to the end of the pipe, since the strain gauge is 6 inches away, I should obtain a value of approximately 30 micro strain. This is due to the Modulus of Elasticity of he Steel pipe and bending stress being applied. I am just not sure how to equate this into a code using the given circuit set up to obtain the desired output values.
It still is not clear what you want to do.
The strain gauge strips are uncalibrated, and until you calibrate them, they can't be used to measure anything. They can only be used to detect whether the local geometry of the object to which they are properly attached has changed.
If you are confident in your strain calculations, then measure the resistance change of a strain gauge (properly affixed to your setup) for a series of "known" strains, and calculate the calibration parameters.
Strain gauges are normally used as pairs, or as two pairs, in a bridge arrangement. This helps with the temperature compensation.
Example of strain gauge load cell construction: https://instrumentationtools.com/strain-gauge-load-cell/
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Yes.
@jdug, you should replace R1 in your diagram with a second strain gauge attached to the opposite side of the beam so that it compresses while the first one expands and vice versa. This will not only help compensating the delta-R / delta-T of the strain gages but will also double the delta-V output of the bridge circuit for a given strain.
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If R1 goes down from compression, while Rsg goes up from expansion, it will raise the voltage at both ends of the bridge. Replacing R2 or R3 with an oppositely-strained gauge would constructively unbalance the bridge.
You're correct.
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