HX711–24 Bit Analog to Digital Converter (ADC)

HX711 is an ADC chip with preamplifier included. The chip is specifically designed for weight scales applications. The load cells which usually measure weight provide voltage outputs in millivolts. These outputs are difficult to handle directly by controllers, so we can use HX711 IC which takes these voltage signals and provide standard digital values which can be used by a microcontroller. The chip has integrated preamplifier specifically to handle these low voltages.

HX711 Pin Configuration

HX711 is a16 pin device.The chip is available in various packages choose one based on your requirement. The description for each pin is given below.

Pin No.	Pin Name	Function	Description
1	VSUP	Power	Regulator supply: 2.7to 5.5V
2	BASE	Analog Output	Regulator control output (NC when not used）
3	AVDD	Power	Analog supply: 2.6 to 5.5V
4	VFB	Analog Input	Regulator control input (connect to AGND when not used）
5	AGND	Ground	Analog Ground
6	VBG	Analog Output	Reference bypass output
7	INA-	Analog Input	Channel A negative input
8	INA+	Analog Input	Channel A positive input
9	INB-	Analog Input	Channel B negative input
10	INB+	Analog Input	Channel B positive input
11	PD_SCK	Digital Input	Power down control (high active) and serial clock input
12	DOUT	Digital Output	Serial data output
13	XO	Digital I/O	Crystal I/O (NC when not used）
14	XI	Digital Input	Crystal I/O or external clock input, PIN is LOW: use on-chip oscillator
15	RATE	Digital Input	Output data rate control, PIN is LOW: 10Hz; PIN is HIGH: 80Hz
16	DVDD	Power	Digital supply: 2.6 to 5.5V

HX711 Features and Specifications

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 andADC analog power supply
On-chip oscillator requiring no externalcomponent with optional external crystal
On-chip power-on-reset
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
Current consumption:normal operation < 1.5mA, power down < 1uA
Operation supply voltage range: 2.6V to 5.5V
Operation temperature range: -40℃ to +85℃

Where to use HX711?

To measure weight using load cell we usually need-regulated power source, output amplifier (noise reduced), ADC converter. All three features need three separate circuits and components adding to cost and complexity. So we can use HX711 IC which has all the above features simply removing complex circuitry.

How to use HX711?

For understanding the usage of HX711 chip let us consider the application circuit shown below.

As shown in circuit, for connecting the load cell to a microcontroller using HX711 we need a few more components. These components perform various functions and are compulsory.

As shown in circuit above, the weight sensor (load cell) draws power from HX711 chip so no other separate power source is needed. The load cell produces analog voltage signal at the output depending the weight applied on its surface (for further understanding study working of load cell).This analog signal is given to PGA (amplifier) through multiplexer. The PGA amplifies the signal and provides output to digital interface. The digital interface converts analog signal to digital value and provides serial data at the output. The controller is connected to the HX711 through I2C interface. The controller gets the serial data which directly relates to the weight sensed by load cell.

Communicating to HX711 chip is difficult for beginners as we need to follow specific steps. And any error will lead to major value deviation. So for beginners using pre written libraries for HX711 will make communication easy.

With conversion of LOAD CELL analog signal to SERIAL DIGITAL DATA the function on ‘HX711 IC’ is done.