Arduino Forum

Using Arduino => General Electronics => Topic started by: daanslag on May 11, 2018, 03:44 pm

Title: 2 load cells and sparkfun load cell amp
Post by: daanslag on May 11, 2018, 03:44 pm
Hello, i am a bit new to arduino and i am trying to make a scale with 50kg load sensors. i got a sparkfun load cell amp. i first conected one load sensor to the amp but i keep getting 0.0kg as a reading. i tried connecting it a lot of differend ways but i was not able to get it. i hope that there is someone who knows wat the problem is and is able to help me.

would mean a lot to me.

greetings,

daniel
Title: Re: 2 load cells and sparkfun load cell amp
Post by: daanslag on May 11, 2018, 03:51 pm
the sensors that i am using have three wires: red, white and black. in the attachments there are some pictures of how i connected them.


the beginning of the calibration code is as follows:
#include "HX711.h"



HX711 scale(6, 7);

float calibration_factor = -7050; //-7050 worked for my 440lb max scale setup
Title: Re: 2 load cells and sparkfun load cell amp
Post by: ted on May 12, 2018, 05:23 am
the sensors that i am using have three wires: red, white and black.
Wrong sensor, you need 4 wires sensor.

https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide/hardware-hookup-
Title: Re: 2 load cells and sparkfun load cell amp
Post by: Wawa on May 12, 2018, 05:48 am
A single load cell needs a set of very accurately matched resistors for the other half of the bridge.
Two 3-wire load cells are needed to make a full bridge.
Four are needed to make personal scales.
Sparkfun has a 'Load Combinator" board to make that easier.
Leo..
Title: Re: 2 load cells and sparkfun load cell amp
Post by: daanslag on May 12, 2018, 11:51 am
thanks for the quick replies! @ Wawa,  i got two load cells. i need to make a scale that ways water underground. is it possible to do a messurement with that full bridge or do i realy need 4 load cells? if so, i was thinking of buying a personal scale and remove the 4 load cells from that, as they also use four, 3 wire, loadcells. and than indeed combining them with the combinator board.

greetings,

Daniel
Title: Re: 2 load cells and sparkfun load cell amp
Post by: Wawa on May 13, 2018, 12:49 am
If you have two load cells...

Measure them with a DMM, and find the two wires with the highest resistance.
Connect them to E+ and E-. Both load cells.
But, opposite polarity/colours. (assuming that forces are in the same direction on both cells).

Then connect the two remaining wires, one to A+ and one to A-
Leo..