Electronic scale with HX711 load cell and Arduino Uno

HX711 Modul and weight cell

Load cells
Load cells are a special form of taking up thrust (force sensors) for the construction of weighing devices, also for weighing with scales. They are calibrated in grams (g) kilograms (kg) or tons (t), not in Newton (n) as the force sensors.

Construction
Load cells usually contain a spring body, a suitably shaped piece of metal whose geometry changes slightly under the action of weight. This elastic deformation is detected for weights of a few grams up to several thousand tons of strain gages and converted into an electrical signal.

Measuring principle
The HX711 chip use the Wheatstone bridge principle as a measuring circuit. It measuring the electrical resistances changes and convert it into an electrical signal.
The circuit is made up of four resistors, which are connected together to form a closed ring or a square with a voltage source in one diagonal and a voltmeter in the other.

Wheatstone bridge circuit

It was invented in 1833 by Samuel Hunter Christie, but named after the British physicist Sir Charles Wheatstone, who recognized their importance and promoted their dissemination.

Wiring
Arduino Uno          HX711            
5V                >         VCC             
GND            >         GND        
Pin 4            >         DT           
Pin 5            >         SCK        


HX711                    Load cell
E+               >         red
E-                >         black
A-                >         white
A+               >         green

Wiring schematic

Make Arduino IDE ready
- Open your Arduino IDE and go to Library Manager (Sketch > Include Library > Library Manager) 

- Type HX711_ADC by Olav Kallhovd and install it

Installing HX711_ADC library from Library Manager

Code

Open Arduino IDE, select Arduino UNO as your MCU, connect your Arduino to your computer, paste the code below and compile it.

Calibration
Make sure to set the calibration factor after fixing your weight cell in the right position. The calibration factor depends on your personal fixing of the weight cell. It is recommended to use a reference weight.

Pictures/Video
Pictures of the construction and a testing video will follow shortly if I find time to make it.

Source

Wikipedia