Weight sensor 0 - 1Kg + HX711 load cell amplifier, Gravity

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.

Technical details

• Load cell size: voir images
• Load range: 1 Kg
• HX711 datasheet (pdf)
• Arduino library (GitHub, Sparkfun)
• DFRobot Library (GitHub, DFRobot)

HX711 specifications

• 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

Load cell

• Range:1kg
• 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