I've been trying to setup a quarter-bridge just to test the sensors before making the full-bridge. The resistors and strain gauge all show 120 ohms and the resistance does vary on the multimeter when I flex the material, however, when I build the circuit the HX711 output is constantly 8388608 suggesting it is saturated. Is my circuit wrong or is it possible the HX711 is damaged? Many thanks in advance!
Excitation should be across 2 resistors, not 1. Output should be across 2 resistors.
Try swapping the red and white wires.
2 Likes
Thank you for the reply! I gave that a whirl and it certainly isn't static and saturated, it is now fluctuating between 4700-5000. There is no noticeable change when the material is flexed however.
Sorry, I have no experience with the HX11 modules, so can't be any help with that. Those modules seem to be popular with the folk that make scales.
Do you have a DMM? Power the setup. Measure the voltage from E+ to E-. Should, of course, measure the intended excitation voltage. Measure from O+ to O-. Should be near 0. What do you get?
Sorry, but that is almost certainly not correct!
They may be approximately 120 Ohms and the 1% resistors may be very closely matched, but the strain gauge is unlikely to be anywhere near the same resistance, so the bridge will be completely out of balance as the reading indicates.
You would need to provide a potentiometer - a value of about 5 Ohms I would guess (which is not going to be easy) - to insert between the two resistors opposite the strain gauge in order to adjust the balance.
For this reason, most strain gauges are themselves a "potentiometer" with three leads which is already closely balanced at rest, allowing a far more stable measuring arrangement.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.