Force / load sensor to measure weight from 0 to 1 Kg - Load cell and HX711 cell amplifier
The HX711 integrated circuit also called "Load Cell Amplifier" is used to measure a load cell and, therefore, to measure a weight. By connecting the amplifier to a microcontroller, it is then possible to read the resistance of the load cell. Note that a calibration process is necessary to be able to make very precise weight measurements.
The load cells + amplifier are really very practical for creating your own scales, process control or simple presence detector.
The HX711 uses a two wire interface to transmit the data and clock signal (clock/sck and data/dout) to communicate with any microcontroller. Many libraries exist on the Internet, which makes it very easy to read data from the HX711.
A load cell uses a 4-wire H-Bridge heatstone (Wikipedia, english version), which wires are connected to the HX711 amplifier. These wires follow a standardized color code to facilitate connections Red (RED), Black (BLK), White (WHT), Green (GRN). Colors which, in the case of a load cell, follow a coding convention:
- Red (Excitation+ or VCC)
- Black (Excitation- or GND)
- White (Amplifier+, Signal+ or Output+)
- Green (A-, S- or O-)
- Yellow (When present. Mass)
If the HX711 module works with a voltage of 2.7 to 5V, the load cell does not!
This requires an excitation voltage of 5 to 15V. Therefore, this board must absolutely be supplied with 5V and therefore only suitable for 5V microcontrollers like an Arduino UNO.
For use with 3.3V microcontroller, a logic level converter must be used for the data signals.
- Analog to Digital converter
- Two selectable differential input channels
- On-chip active low noise PGA with selectable gain of 32, 64 and 128
- On-chip power supply regulator for load-cell and ADC analog power supply
- On-chip oscillator requiring no external component with optional external crystal
- On-chip power-on-rest
- Simple digital control and serial interface: pin-driven controls, no programming needed
- Selectable 10SPS or 80SPS output data rate
- Simultaneous 50 and 60Hz supply rejection
- Supply Voltage: 2.6V~5.5V
- Current: < 1.6mA
- Working temperature: -40~85°C
- 16 pin SOP-16 package
- Excitation voltage: 5-15 V
- Output sensitivity: 1.0 +/- 0.15mV/V
- Synthetical error: 1 per thousand cent of full scale
- Zero shift: 0.05/0.03 （30min）%F.S
- Zero temperature shift: 0.05/0.03 %F.S/10°C
- Zero output: +/- 0.1mV/V
- Input impedance: 1055 +/- 15 Ohms
- Output impedance: 1000 +/- 5 Ohms
- Overload capability: 200 %F.S
- Output: Analog output
- Size: 33mm x 38mm
The weight sensor is not reversible!
Please, follow the assembly indication (positionning, screwing, arrow) with care!
An arrow do indicate the side of the sensor where the weight must be applied and the direction to the force to be applied by the weight.