Overview

The HX711 is a precision 24-bit analog-to-digital converter (ADC) manufactured by Avia Semiconductor. It is specifically designed for weigh scales, strain-gauge load cells, and industrial process control applications.

The chip integrates a low-noise programmable gain amplifier (PGA), power supply regulator for sensor and ADC analog front-end, clock oscillator, and a 2-wire serial interface (PD_SCK and DOUT).

Quick reference

Operating voltage (VCC)2.6 V to 5.5 V DC
ADC resolution24-bit differential
Input channels2 Differential Channels (Channel A & Channel B)
Programmable Gain (Ch. A)128 (default) or 64
Fixed Gain (Ch. B)32
Output Data Rate10 SPS or 80 SPS (pin-selectable via RATE)
Communication interface2-wire serial (PD_SCK, DOUT)
Power-down current< 1 µA

Pinout

Standard HX711 Breakout Module Pins

PinNameTypeDescription
1E+ / VCC_LOADPower OutputExcitation power positive (to load cell Red wire)
2E- / GND_LOADPower OutputExcitation power negative / Ground (to load cell Black wire)
3A+ / INA+Analog InputChannel A differential input positive (to load cell Green wire)
4A- / INA-Analog InputChannel A differential input negative (to load cell White wire)
5B+ / INB+Analog InputChannel B differential input positive (optional second sensor)
6B- / INB-Analog InputChannel B differential input negative (optional second sensor)
7VCCPowerDigital logic supply voltage (+2.6 V to +5.5 V)
8GNDPowerDigital Ground (0 V)
9DT / DOUTDigital OutputSerial data output pin
10SCK / PD_SCKDigital InputPower-down and serial clock input pin

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}2.65.05.5V
Analog Input Full-Scale (Ch. A, Gain 128)VIDV_{ID}—±20\pm 20—mVVREF=4.5 VV_{REF} = 4.5\text{ V}
Analog Input Full-Scale (Ch. A, Gain 64)VIDV_{ID}—±40\pm 40—mVVREF=4.5 VV_{REF} = 4.5\text{ V}
Analog Input Full-Scale (Ch. B, Gain 32)VIDV_{ID}—±80\pm 80—mVVREF=4.5 VV_{REF} = 4.5\text{ V}
Output Data Rate (RATE = 0)fSPSf_{SPS}—10—HzLow noise, 50/60Hz rejection
Output Data Rate (RATE = 1)fSPSf_{SPS}—80—HzFast sample rate
Normal Operating CurrentICCI_{CC}—1.52.1mAVCC=5.0 VV_{CC} = 5.0\text{ V}
Power-Down CurrentIpdI_{pd}—0.51.0µAPD_SCK=HIGHPD\_SCK = HIGH for >60 μs>60\text{ }\mu\text{s}

Communication protocol

Communication with the HX711 uses a simple bit-banging protocol over PD_SCK and DOUT:

  1. When data is ready for retrieval, DOUT goes LOW.
  2. Apply 24 clock pulses to PD_SCK to shift out the 24-bit raw conversion result (MSB first).
  3. Apply 1, 2, or 3 additional clock pulses (total 25, 26, or 27 pulses) to select the channel and gain for the next conversion:
    • 25 pulses: Channel A, Gain 128
    • 26 pulses: Channel B, Gain 32
    • 27 pulses: Channel A, Gain 64
text
DOUT    ───┐                                          ┌───
           └──────────────────────────────────────────┘
PD_SCK  _____┌─┐_┌─┐_ ... _┌─┐_┌─┐_┌─┐_______________
Pulse #      1   2         24  25  26 (Gain/Ch select)

Wiring

Load Cell to HX711 Module Wiring

Load Cell Wire ColorStandard SignalHX711 Terminal
RedExcitation + (E+)E+
BlackExcitation - (E-)E-
GreenSignal + (A+)A+
WhiteSignal - (A-)A-

HX711 Module to Microcontroller

HX711 Pin→Microcontroller (Arduino Uno / ESP32)
VCC5V (or 3.3V)
GNDGND
DT / DOUTDigital Pin 3 (GPIO input pin)
SCK / PD_SCKDigital Pin 2 (GPIO output pin)
Warning

High PD_SCK Hold Time Enters Power-Down Mode: If PD_SCK is held HIGH for longer than 60 µs, the HX711 enters sleep mode and powers off internal circuitry. Ensure microcontroller interrupts do not freeze PD_SCK HIGH during serial reads.

Common mistakes

  • Leaving RATE pin floating: On some modules, the RATE pin selects sample rate (10 Hz vs 80 Hz). Floating RATE can cause intermittent noise or sample rate drops.
  • Handling 24-bit 2's complement sign extension: The HX711 returns a 24-bit signed integer. When storing in a 32-bit int32_t variable, if bit 23 is 1 (negative number), you must perform sign extension by OR-ing with 0xFF000000.
  • Powering load cell from noisy rail: Load cell readings drift significantly if supply voltage is unstable. Ensure the onboard regulator on the HX711 module is active and properly decoupled.

Notes

  • Calibration requires taking a tare (zero-weight offset) reading followed by placing a known calibration weight on the scale to compute the scale factor (Weight=Raw Reading−TareScale Factor\text{Weight} = \frac{\text{Raw Reading} - \text{Tare}}{\text{Scale Factor}}).

Assets & downloads