HX711 Load Cell Amplifier C Driver

Overview

The HX711 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications. This C driver enables communication with the HX711 module using a microcontroller over a digital interface. The communication is achieved via a two-wire protocol (DATA and CLOCK).

Currently, the example only supports STM32F103. Feel free to contact me if you need assistance or wish to develop additional features.

Features

• Interface with load cells for weight measurement.
• High precision 24-bit ADC.

Hardware Requirements

• Microcontroller (e.g., STM32, AVR, ESP32, etc.)
• HX711 Load Cell Amplifier module
• 2 GPIO pins for DATA and CLOCK signals

Example

Note: Currently supports an STM32 example, tested on STM32F103C8T6. The example reads the load cell value and prints it out through UART.

• example\stm32\calib_find_ref_weight_value: it is there if the user want to calibrate the scale instead of using author's default values
• example\stm32\basic_read_weight: auto tare, print out the result through uart

Used Peripherals:

• GPIO: for read/clock out data from hx711
• TIMER: to make a delay function
• UART: print out results
• Utils:
  • float to string conversion

Wiring Diagram

For example STM32F103C6T6, you can find the information in inc/board_config.h or below:

HX711 Pin	MCU Pin
VCC	3.3 - 5V
GND	GND
DT (DATA)	GPIO_B8
SCK (CLOCK)	GPIO_B9

---

| UART (TX) | GPIO_A9 |

Installation

1. Copy driver files (hx711.c, hx711.h) into your project.
2. Include the header file in your source code:

   #include "hx711.h"

Usage

(Optional - referably) Calibration

1. Find the example calib_find_ref_weight_value, build and flash the firmware to mcu
   • cd ./example/stm32/calib_find_ref_weight_value
   • make clean
   • make Flash the `./build/calib.elf' to your mcu
2. Observes the output throught UART: i.e.

[Calib] object weight: 188(g) | ref value: 7873649
[Calib] object weight: 188(g) | ref value: 7877023
[Calib] object weight: 188(g) | ref value: 7873680
[Calib] object weight: 188(g) | ref value: 7873692
[Calib] object weight: 188(g) | ref value: 7873630
[Calib] object weight: 188(g) | ref value: 7873643
[Calib] object weight: 188(g) | ref value: 7873606
[Calib] object weight: 188(g) | ref value: 7873635

3. Note down your value (i.e 188, 7873635)
4. Find the example calib_find_ref_weight_value, build and flash the firmware to mcu
   • back to project directory
   • cd ./example/stm32/basic_read_weight
   • Find main.c and init it with your ref values

   hx711_init(HX711_GAIN_128, true, 188, 7873635);

• make clean
• make Flash the `./build/hx711_loadcell.elf' to your mcu

5. Observe the output:

Weight: 0.16016(g) // when not place anything
Weight: 0.14063(g)
Weight: -597.15234(g) // communication error
Weight: 0.36914(g)
Weight: 0.33789(g)
Weight: 0.29883(g)
Weight: 0.24609(g)
Weight: 206.10937(g) // when I put my phone one the scale
Weight: 206.19531(g)
Weight: 206.07421(g)
Weight: 206.22070(g)
Weight: 206.08007(g)
Weight: 206.03710(g)
Weight: 206.13476(g)
Weight: 207.04101(g)
Weight: 0.14844(g) // when I took it out
Weight: 0.12891(g)
Weight: 0.18359(g)
Weight: 0.32227(g)

Initialize hardware abstraction for HX711

void hx711_com_init(void)
{
    hx711_hw_ops_t hx711_ops = {
            .read = hal_gpio_read,
            .write = hal_gpio_write,
            .delay_us = hal_delay_us,
    };
    hx711_set_hw_ops(&hx711_ops);
}

int32_t hx711_get_weight(void)
{
        return hx711_read();
}

...

Initialize MCU hardware

    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_USART1_UART_Init();
    hx711_com_init();

Read Weight Data

        sw_udelay(1000000);

        int32_t weight = hx711_get_weight();
        hal_uart_printf("Weight: %d\n", weight);
        HAL_GPIO_TogglePin(BUILTIN_LED_PORT, BUILTIN_LED_PIN);

Results:

I used logic analyzer to print out values

Weight: 0.16016(g) // when not place anything
Weight: 0.14063(g)
Weight: -597.15234(g) // communication error
Weight: 0.36914(g)
Weight: 0.33789(g)
Weight: 0.29883(g)
Weight: 0.24609(g)
Weight: 206.10937(g) // when I put my phone one the scale
Weight: 206.19531(g)
Weight: 206.07421(g)
Weight: 206.22070(g)
Weight: 206.08007(g)
Weight: 206.03710(g)
Weight: 206.13476(g)
Weight: 207.04101(g)
Weight: 0.14844(g) // when I took it out
Weight: 0.12891(g)
Weight: 0.18359(g)
Weight: 0.32227(g)

Notes

• HX711 operates at 5V but can also work at 3.3V with reduced performance.

Performance evaluation:

Here is my setup:

1. Clock timing: As I set each clock is 10us using stm32f103c6t6 timer, by using salae logic analyzer, I'm able to measure each clock bit is ~10us to 12us.

2. Sampling rate: I set the sampling rate to be 10Hz, the result is ~10Hz with the data measuring time less than 100ms (~60ms):

3. Accuracy: The accuracy is depended on the calibration, here I just want to evaluation the noise, which causes err of +-0.1g

Weight: -1.08594(g)
Weight: -1.00781(g)
Weight: -1.09570(g)
Weight: -1.05859(g)
Weight: -1.10156(g)
Weight: -1.11328(g)
Weight: -1.08203(g)
Weight: -1.06445(g)
Weight: -1.11719(g)
Weight: -1.15430(g)
Weight: -1.18359(g)
Weight: -1.11523(g)
Weight: -1.05664(g)
Weight: -1.11133(g)
Weight: -1.10547(g)
Weight: -1.09375(g)
Weight: -1.18945(g)
Weight: -1.08984(g)

Power Consumption Evaluation

• Measurement device: Nordic PPK2
• Condition: Input supply to VCC (main power source)
• Result: 5.5mA @ 5V when up 26.23uA @ 5V when down

License

This driver is open-source and can be used freely in any project.

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Author: Binh Pham
Contact me: You can find my contact @ https://github.com/ch-binh
Version: 1.0
Last Updated: March 2025