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[ybl84f1]

I'm connecting 4 strain gauges (stripped out of a bathroom scale) to the Combinator -> HX711 -> Arduino, pretty much like the Sparkfun example online but I'm not getting any valid readings. (I built a previous prototype and it did work). I am using the "bogde" library and using a scope I can see the HX711 communications look good. (The first data bit is a 1 and the following 23 data bits are 0's).

I measured the strain gauges to determine the center tap and connected the to "C" on the Combinator. For the other connections I went by the recommended color code.

On the Combinator board the excitation voltage is ~3.3V, the voltage on the white is ~1V, and the voltage on the green is about 2V.


Questions:

1) Could my issue be as simple as the remaining two wires (for each of the 4 strain gauges) need to be reversed? (I know I have the center tap correct).

2) Even though all 4 strain gauges came out of the scale and are coded the same, could the two wires from each gauge (not the center tap) not be consistent? (I.e. could one or more of the strain gauges be connected incorrectly?)

3) Knowing the change in resistance is beyond the capability of my multimeter, is there a simple way to determine which wire from the strain gauge is the variable and which one is fixed?

Any thoughts/comments/suggestions appreciated!

[ybl84f1]

Sorry folks - I'm embarrassed to say it was user error, the wiring color on my 4 strain gauges (stripped from a bathroom scale) was different than gauges from a similar scale (even though the colors are identical).

I'm still not sure why there are 3 wires from a strain gauge (and why the Combinator needs them) when it is essentially a 2-wire variable resistor, or what the Combinator does with the third wire, or what happens when they're reversed but that will have to wait another day.

FYI for those interested this is for a remote wireless scale to measure beer keg weight inside a kegerator. It uses 4 bathroom scale strain gauges, a nRF24L01 radio and Arduino Pro 3.3V running on 6 AA batteries to report weight back to a Pi controller.

[darrellg]

I'm still not sure why there are 3 wires from a strain gauge (and why the Combinator needs them) when it is essentially a 2-wire variable resistor, or what the Combinator does with the third wire, or what happens when they're reversed but that will have to wait another day.

From https://learn.sparkfun.com/tutorials/lo ... okup-guide: