Out of tree HX711 sensor driver module for Zephyr RTOS

HX711 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scale applications.

Supported and tested Zephyr versions

• 3.3.0 (February 2023)
• 3.2.0 (September 2022)
• 2.7.0 LTS2 Release (October 2021)

Usage

Module installation for projects using west modules

Add this project to your west.yml manifest:

- name: HX711
  path: modules/HX711
  revision: refs/tags/zephyr-v3.2.0
  url: https://github.com/nobodyguy/HX711_zephyr_driver

So your projects should look something like this:

manifest:
  projects:
    - name: zephyr
      url: https://github.com/zephyrproject-rtos/zephyr
      revision: refs/tags/zephyr-v3.2.0
      import: true
    - name: HX711
      path: modules/HX711
      revision: refs/tags/zephyr-v3.2.0
      url: https://github.com/nobodyguy/HX711_zephyr_driver

This will import the driver and allow you to use it in your code.

Additionally make sure that you run west update when you've added this entry to your west.yml.

Module installation for projects not using west modules directly

1. Create directory named modules inside project root directory.
2. Clone this repository into modules as HX711 directory
3. Edit CMakeLists.txt in your project's root directory:

set(ZEPHYR_EXTRA_MODULES "${CMAKE_SOURCE_DIR}/modules/HX711")
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

Driver configuration

Enable sensor driver subsystem and HX711 driver by adding these entries to your prj.conf:

CONFIG_SENSOR=y
CONFIG_HX711=y

Define HX711 in your board .overlay like this example:

/{
	hx711 {
		compatible = "avia,hx711";
		status = "okay";
		label = "HX711";
		dout-gpios = <&gpio0 26 (GPIO_ACTIVE_HIGH | GPIO_PULL_UP) >;
		sck-gpios = <&gpio0 27 GPIO_ACTIVE_HIGH>;
		rate-gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>;
	};
};

There are also optional output filters that you can enable and configure. The first one is a median filter to discard any peak values.

CONFIG_HX711_ENABLE_MEDIAN_FILTER=y
CONFIG_HX711_MEDIAN_FILTER_WINDOW_SIZE=3

The second one is an exponential moving average (EMA) to smooth out the output.

CONFIG_HX711_ENABLE_EMA_FILTER=y
CONFIG_HX711_EMA_FILTER_ALPHA_FACTOR=50

Driver usage

#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/devicetree.h>
#include <zephyr/drivers/sensor.h>
#include <zephyr/logging/log.h>
#include <zephyr/sys/util.h>
#include <zephyr/types.h>

#include <sensor/hx711/hx711.h>
#include <stddef.h>

LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);

const struct device *hx711_dev;

void set_rate(enum hx711_rate rate)
{
	static struct sensor_value rate_val;

	rate_val.val1 = rate;
	sensor_attr_set(hx711_dev,
			HX711_SENSOR_CHAN_WEIGHT,
			SENSOR_ATTR_SAMPLING_FREQUENCY,
			&rate_val);
}

void measure(void)
{
	static struct sensor_value weight;
	int ret;

	ret = sensor_sample_fetch(hx711_dev);
	if (ret != 0) {
		LOG_ERR("Cannot take measurement: %d", ret);
	} else {
		sensor_channel_get(hx711_dev, HX711_SENSOR_CHAN_WEIGHT, &weight);
		LOG_INF("Weight: %d.%06d grams", weight.val1, weight.val2);
	}
}

void main(void)
{
	int calibration_weight = 100; // grams
	hx711_dev = DEVICE_DT_GET_ANY(avia_hx711);
	__ASSERT(hx711_dev == NULL, "Failed to get device binding");

	LOG_INF("Device is %p, name is %s", hx711_dev, hx711_dev->name);
	LOG_INF("Calculating offset...");
	avia_hx711_tare(hx711_dev, 5);

	LOG_INF("Waiting for known weight of %d grams...",
		calibration_weight);

	for (int i = 5; i >= 0; i--) {
		LOG_INF(" %d..", i);
		k_msleep(1000);
	}

	LOG_INF("Calculating slope...");
	avia_hx711_calibrate(hx711_dev, calibration_weight, 5);

	while (true) {
		k_msleep(1000);
		LOG_INF("== Test measure ==");
		LOG_INF("= Setting sampling rate to 10Hz.");
		set_rate(HX711_RATE_10HZ);
		measure();

		k_msleep(1000);
		LOG_INF("= Setting sampling rate to 80Hz.");
		set_rate(HX711_RATE_80HZ);
		measure();
	}
}

Relevant prj.conf:

CONFIG_SENSOR=y
CONFIG_HX711=y
CONFIG_LOG=y