Half Bridge Load Cell Problem

Other Hardware Sensors
1

Hello, i have a problem with the half bridge load cell reading.

i already wired the half bridge with the hx711 exactly like this pict

and im using this code

#include "HX711.h"

HX711 scale(5, 6);

float calibration_factor = 1000; // this calibration factor is adjusted according to my load cell
float units;
float ounces;

void setup() {
  Serial.begin(9600);
  Serial.println("HX711 calibration sketch");
  Serial.println("Remove all weight from scale");
  Serial.println("After readings begin, place known weight on scale");
  Serial.println("Press + or a to increase calibration factor");
  Serial.println("Press - or z to decrease calibration factor");

  scale.set_scale();
  scale.tare();  //Reset the scale to 0

  long zero_factor = scale.read_average(); //Get a baseline reading
  Serial.print("Zero factor: "); //This can be used to remove the need to tare the scale. Useful in permanent scale projects.
  Serial.println(zero_factor);
}

void loop() {

  scale.set_scale(calibration_factor); //Adjust to this calibration factor

  Serial.print("Reading: ");
  units = scale.get_units(), 10;
  if (units < 0)
  {
    units = 0.00;
  }
  ounces = units * 0.035274;
  Serial.print(units);
  Serial.print(" kg"); 
  Serial.print(" calibration_factor: ");
  Serial.print(calibration_factor);
  Serial.println();
  delay(500);

  if(Serial.available())
  {
    char temp = Serial.read();
    if(temp == '+' || temp == 'a')
      calibration_factor += 1;
    else if(temp == '-' || temp == 'z')
      calibration_factor -= 1;
  }
}

i already tried to calibrate the sensor but the reading always inconsistent, its jumping around even with no load on the sensor. the value cant stay on 0.

anybody know the solution?

thanks

2

You realize the two 1k resistors have to be high quality precision metal film?

3

It sounds like your power is not clean. The HX711 is a precision 24-bit analog- to-digital converter ... interface directly with a bridge sensor. The input ... power for the ADC and the sensor. The A/D is measuring uV so noise is a real problem. I would suggest you spend some time studying Analog Circuits and how to implement them paying attention to very low level signals in the micro-volt range.

4

MarkT:
You realize the two 1k resistors have to be high quality precision metal film?

hey, its my fault. i put 10k resistor instead of 1k.

bbut i replaced to 1k resistor, then i got no reading at all.

im using the blue resistor with 1% tolerance (5 strip, brown tolerance). should i try using the cream one with 5% tolerance( 4 strip, gold tolerance)?

5

panducdrmwn:

HX711 scale(5, 6);

anybody know the solution?

Making sure pin assignments in your code match your actual wiring goes a long way.

6

panducdrmwn:
im using the blue resistor with 1% tolerance (5 strip, brown tolerance). should i try using the cream one with 5% tolerance( 4 strip, gold tolerance)?

No, the metal film 1% is much better. 0.1% precision metal film resistors or better is what you should be using though.

The important thing is that they have identical values, around a k ohm or so, thus forming a high precision
1:1 divider for one arm of the bridge.

Check the resistance between red/white and between red/black are the same in the load-cell. They form
the other arm of the bridge.