HX711 Analog Digital Converter (ADC)
Overview
The Boardoza HX711 is a precision 24-bit analog-to-digital converter designed specifically for weigh scales and industrial control applications to interface directly with a bridge sensor. Built around the Avia Semiconductor HX711 architecture, this module integrates a low-noise programmable gain amplifier (PGA) and a regulated power supply, providing a complete "front-end" solution for load cells.
Unlike general-purpose ADCs, the HX711 is optimized for small-signal differential measurements. It eliminates the need for external active components by incorporating on-chip power supply regulators and an on-chip oscillator, drastically reducing the bill of materials and PCB footprint for high-precision force sensing systems.
Core Technical Specifications
The module is defined by the following operational parameters:
Resolution: 24-bit output precision, capable of resolving extremely minute voltage changes typical of strain gauge bridges.
Input Channels: Features two selectable differential input channels (Channel A and Channel B). Channel A is programmable with a gain of 64 or 128, while Channel B has a fixed gain of 32.
Low-Noise PGA: The integrated Programmable Gain Amplifier enables direct interfacing with low-output sensors (e.g., 2mV/V load cells) without requiring external instrumentation amplifiers.
Data Rate: User-selectable output data rate of either 10 samples per second (SPS) for high stability or 80 SPS for faster response times.
Power Supply Rejection: Simultaneous 50Hz and 60Hz supply rejection ensures measurement stability in electrically noisy industrial environments.
Operating Voltage: Supports a wide supply range from 2.6V to 5.5V, making it compatible with both 3.3V and 5V logic systems.
Current Consumption: Low operating current (<1.5 mA) and an integrated power-down mode (<1 µA) suitable for battery-powered scales.
Key Engineering Features
Specialized Bridge Interface
The module is engineered to drive Wheatstone bridge sensors directly. It provides the excitation voltage (E+ and E-) and reads the differential signal voltage (A+ and A-). The on-chip analog power regulator simplifies the power distribution network, ensuring that the excitation voltage remains stable relative to the ADC reference, which is critical for ratiometric measurement accuracy.
Digital Interface Protocol
The HX711 utilizes a custom two-wire serial interface (Clock and Data) that is similar to, but not compatible with, standard SPI. This "bit-banging" protocol allows the host microcontroller to retrieve the 24-bit conversion result and simultaneously configure the gain and channel selection for the next conversion cycle via the number of clock pulses sent.
On-Chip Oscillator
The internal on-chip oscillator requires no external crystal or capacitor, simplifying board layout and reducing susceptibility to EMI. This robust clock generation ensures consistent timing for the Sigma-Delta modulator and digital filter stages.
Hardware Interface and Signal Mapping
The breakout board features standard headers divided into sensor-side (Analog) and MCU-side (Digital) connections:
Sensor Interface (Analog Side)
E+ (Excitation Positive): Regulated power output to the load cell (Red wire).
E- (Excitation Negative): Ground return for the load cell (Black wire).
A- (Signal Negative): Negative differential input from the load cell (White wire).
A+ (Signal Positive): Positive differential input from the load cell (Green wire).
B- / B+: Inputs for the secondary, lower-gain channel (often used for battery monitoring).
Host Interface (Digital Side)
VCC: Power input (2.6V - 5.5V).
DT (Data): Serial Data Output. Outputs the 24-bit data in 2's complement format.
SCK (Clock): Serial Clock Input. Controls the data retrieval timing and gain selection.
GND: Digital ground reference.
Applications
Electronic Scales: Kitchen scales, bathroom scales, and postage meters.
Industrial Weighing: Hopper scales, platform scales, and conveyor belt monitoring.
Force Sensing: Strain gauge measurement for structural health monitoring.
Tactile Sensors: Robotics pressure sensing and grip force feedback.
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