Hi guys,
I'm currently working on a small project that consists of:
1 x Arduino Uno
1 x HX711
1 x Breadboard
1 x Load Cell from 0.1g to 500g Jewelry Scale from Ebay. I took the load cell out of that.
http://www.ebay.com.au/itm/172127193402
My project is to measure the weight of products between 0.1g to around 500g, so nothing too heavy. I hooked everything up and used the code from Sparkfun to calibrate my scale. The way I hooked everything up is identical to the image below(image from Sparkfun).
NOTE: The the green wire above is blue in my situation
When I run the code:
/*
Example using the SparkFun HX711 breakout board with a scale
By: Nathan Seidle
SparkFun Electronics
Date: November 19th, 2014
License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).
This is the calibration sketch. Use it to determine the calibration_factor that the main example uses. It also
outputs the zero_factor useful for projects that have a permanent mass on the scale in between power cycles.
Setup your scale and start the sketch WITHOUT a weight on the scale
Once readings are displayed place the weight on the scale
Press +/- or a/z to adjust the calibration_factor until the output readings match the known weight
Use this calibration_factor on the example sketch
This example assumes pounds (lbs). If you prefer kilograms, change the Serial.print(" lbs"); line to kg. The
calibration factor will be significantly different but it will be linearly related to lbs (1 lbs = 0.453592 kg).
Your calibration factor may be very positive or very negative. It all depends on the setup of your scale system
and the direction the sensors deflect from zero state
This example code uses bogde's excellent library: https://github.com/bogde/HX711
bogde's library is released under a GNU GENERAL PUBLIC LICENSE
Arduino pin 2 -> HX711 CLK
3 -> DOUT
5V -> VCC
GND -> GND
Most any pin on the Arduino Uno will be compatible with DOUT/CLK.
The HX711 board can be powered from 2.7V to 5V so the Arduino 5V power should be fine.
*/
#include "HX711.h"
#define DOUT 3
#define CLK 2
HX711 scale(DOUT, CLK);
float calibration_factor = -7050; //-7050 worked for my 440lb max scale setup
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: ");
Serial.print(scale.get_units(), 1);
Serial.print(" lbs"); //Change this to kg and re-adjust the calibration factor if you follow SI units like a sane person
Serial.print(" calibration_factor: ");
Serial.print(calibration_factor);
Serial.println();
if(Serial.available())
{
char temp = Serial.read();
if(temp == '+' || temp == 'a')
calibration_factor += 10;
else if(temp == '-' || temp == 'z')
calibration_factor -= 10;
}
}
I get 0g as my starting weight and when I try and calibrate by using the a,z, - or + the the weight doesn't change with or without a known weight. See below.
My first bet would be the type of load cell as I can't find the actual manufacture. I did some voltage testing shown below. They're the same voltage with or without the weight. Maybe too minor to realise the voltage variation?
Voltage across:
Red Wire (E+) and Black Wire (E-): 4.02V.
Red Wire (E+) and Blue Wire (A-): 2.02V
Red Wire (E+) and White Wire (A+): 1.99V
Blue Wire (A-) and White Wire (A+): 0.030V
Black Wire (E-) and Blue Wire (A-): 1.99V
Black Wire (E-) and White Wire (A+): 2.02V
Resistance across:
E+ and E-: 1kOhm
E+ and A-:742Ohm
E+ and A+: 748Ohm
A- and A+: 1kOhm
The voltage output at the output is 30mV with or without the load so that could be causing the issue?.
HOWEVER, when I pull out either A- or A+, I get some readings and I can adjust the calibration factor using the a,z, - and +. See below.
Can someone shed some light on this?. Thank you.