HX711

Arduino library for HX711 24 bit ADC used for load cells and scales.

Description

This HX711 library has an interface which is a superset of a library made by bogde. Some missing functions were added to get more info from the lib.

Another important difference is that this library uses floats. The 23 bits mantisse of the IEE754 float matches the 24 bit ADC very well. Furthermore it gave a smaller footprint.

Main flow

First action is to call begin(dataPin, clockPin) to make connection to the HX711.

Second step is calibration for which a number of functions exist.

tare() measures zero point
set_scale(factor) set a known conversion factor e.g. from EEPROM.
calibrate_scale(WEIGHT, TIMES) determines the scale factor based upon a known weight e.g. 1 Kg.

Steps to take for calibration

clear the scale
call tare() to set the zero offset
put a known weight on the scale
call calibrate_scale(weight)
scale is calculated.
save the offset and scale for later use e.g. EEPROM.

Pricing

Some price functions were added to make it easy to use this library for pricing goods or for educational purposes. These functions are under discussion if they will stay. Another set of function to add weights together didn't make it in the 0.2.0 release, it is on a todo list.

For weight conversion functions see https://github.com/RobTillaart/weight

Notes

Scale values for loadcells

These scale values worked pretty well with a set of loadcells, Use calibrate to find your values.

5 KG loadcell scale.set_scale(420.52);
20 KG loadcell scale.set_scale(127.15);

Connections HX711

A+/A- uses gain of 128 or 64
B+/B- uses gain of 32

Connections

HX711 Pin	Color
E+	red
E-	black
A-	white
A+	green
B-	not connected
B+	not connected

HX711 Pin	Color
E+	red
E-	black
A-	blue
A+	white
B-	not connected
B+	not connected

Temperature

Loadcells do have a temperature related error. This can be reduced by doing the calibration and take the tare at the temperature one also does the measurements.

Another way to handle this is to add a good temperature sensor (e.g. DS18B20, SHT85) and compensate for the temperature differences in your code.

Operation

See examples

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