Multiple Strain Gauge Circuit

[loganhanneman]

Hello!
I am fairly new to the Arduino platform, however I do have some experience from years past.

I am looking for help in fully understanding exactly what I need for a future project.

The project involves multiple (say 10+) strain gauges mounted on steel tubes to measure strain, then from that, to get internal stress in the tubes in real time. Ideally, the program would be set up to alert me if any one of the tubes is nearing yield stress of the material.

I understand that I will need a signal amplifier, such as an HX711 amplifier, for the signal coming from the strain gauges.

Here are a few questions that I am looking to have answered:
1. Can one Arduino board handle that many strain gauge inputs, and if so, what board would the ideal one?
2. Will I need a separate HX711 for each strain gauge input?

Thank you very much for your help!

[FantomT]

1. Can one Arduino board handle that many strain gauge inputs, and if so, what board would the ideal one?
2. Will I need a separate HX711 for each strain gauge input?

1. I'd recommend arduino UNO.
2. Alternative to 10+ HX711 is using analog multiplexer, 2x 74HC4067 - to select one gauge at a time to one HX711

[loganhanneman]

Thank you very much for your help!

I am assuming that I would set up each strain gauge into a Wheatstone Bridge circuit, with the strain gauge being one resistor out of the four, for each of the 10+ locations?

Also, in an effort to combat resistance of long wires running away from the strain gauge location to the Arduino, would you suggest keeping the length of wire running directly from the strain gauge to the Bridge circuit/ HX711 as short as possible?

Thanks again

[FantomT]

Normal bridge configuration, two wires out of each gauge, this is why I type 2 X 74HC4067.
Something like this:



There dual types 74HC4052, but only 4 inputs per IC, so two 4067 running in parallel could be better option, but you get an idea.

Resistance is not important, interference (EMI) is. I think twisted pairs or CAT5 should be o'k for wiring up to 100m. May some low pass filtering at the adc side. Multiplexing solution is lowering scan rate proportionally to the number of the sensor.  How fast registration should be? HX711 is slow, and 10+ would drop update rate below 1sec.