Help using HX711 and Four Load Sensors from Bathroom Scale

Hello!

I've done a bit of research online and am getting a lot of mixed information. Essentially I'm making a scale. I am using an Arduino Uno.

I have four load sensors that I pulled from a scale. They're half-bridge sensors. I've got two currently hooked up to an hx711 and one records weight being pushed as positive, and the other records weight being pushed as negative, which makes sense since they're half-bridge sensors.

I have multiple hx711 boards. Should I be using four, or can I simply use two? If I decide to use two, should I put the load sensors diagonally? Do you guys have any tips?

Edit: My load sensors are three wire load sensors, so I've got the two load sensors hooked up to an HX711 with both power wires going to E+, both grounds going to E-, and each load sensor going to either A- or A+.

One HX711. This page might help with combining four 3-wire cells into one 4-wire load cell. https://www.sparkfun.com/products/13878 Leo..

Wawa: One HX711. This page might help with combining four 3-wire cells into one 4-wire load cell. https://www.sparkfun.com/products/13878 Leo..

Thanks for the reply!

Unfortunately, I don't think we have enough time to wait for a combinator board to come in. Is there an alternative using the current hx711s that I have?

yousefissa:
Thanks for the reply!

Unfortunately, I don’t think we have enough time to wait for a combinator board to come in. Is there an alternative using the current hx711s that I have?

Build one, schematics available at the sparkfun site.
And attached here.

Can you tell us your electronics, programming, Arduino, hardware experience?

Tom… :slight_smile:

SparkFun Load Sensor Combinator v11.pdf (38.7 KB)

TomGeorge: Build one, schematics available at the sparkfun site. And attached here.

Can you tell us your electronics, programming, Arduino, hardware experience?

Tom.. :)

Hey, thanks for the message!

I can try building it. I have a bit of programming experience but this is for a school project that took an unexpected technical turn. I don't have much arduino or hardware experience at all.

Would this work?

https://forum.arduino.cc/index.php?topic=322241.0

Try this

For four half bridge load cells like in a bathroom scale, you only need one hx711 and a wheatstone bridge. The Sparkfun combinator board has no electronic components on it at all - it just tidies up your wiring a lot. You will also need a multi meter to work out the wires from the load cells as there doesn't seem to be a standard colour scheme. This guide has a pretty good rundown, including bathroom scales.

davidrh: For four half bridge load cells like in a bathroom scale, you only need one hx711 and a wheatstone bridge. The Sparkfun combinator board has no electronic components on it at all - it just tidies up your wiring a lot. You will also need a multi meter to work out the wires from the load cells as there doesn't seem to be a standard colour scheme. This guide has a pretty good rundown, including bathroom scales.

Thanks!

I think this was helpful: https://arduino.stackexchange.com/questions/11946/how-to-get-weight-data-from-glass-electronic-bathroom-scale-sensors

"To get this, wire all four sensors in a big ring with maximum resistance, matching colors and initially ignoring the red center tap wires. (This is the function of the soldered-together blues and blacks are in your scale.) Choose two opposite (red) center taps as E+ and E-, and the remaining two (red) center taps as S+,S-. Put the excitation voltage on the E+/E- from the diagram above and read a force-sensitive voltage difference across S+/S-, and this is what you feed into your HX711 as A+ and A- (Ignore B+/B- as a second, unused channel.)"