Out of tree Adafruit NAU7802 loadcell driver module for Zephyr RTOS

NAU7802 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scale applications.

Supported Zephyr versions

• 3.7.0 (May 2024)

Usage

Module installation

Add this project to your west.yml manifest:

 # out of tree device driver
- name: NAU7802_LOADCELL
    path: modules/nau7802_loadcell
    revision: refs/tags/zephyr-v3.7.0
    url: https://github.com/nobodyguy/nau7802_loadcell_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
# out of tree device driver
    - name: NAU7802_LOADCELL
      path: modules/nau7802_loadcell
      revision: refs/tags/zephyr-v3.7.0
      url: https://github.com/TinNotTim/nau7802_loadcell_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.

Driver configuration

Enable sensor driver subsystem and NAU7802 driver by adding these entries to your prj.conf:

CONFIG_SENSOR=y
CONFIG_NAU7802_LOADCELL=y
# Interrut triggerred configurations
CONFIG_NAU7802_LOADCELL_TRIGGER_NONE=y
CONFIG_NAU7802_LOADCELL_TRIGGER_OWN_THREAD=y
CONFIG_NAU7802_LOADCELL_TRIGGER_GLOBAL_THREAD=y
CONFIG_NAU7802_LOADCELL_TRIGGER_DIRECT=y

Define NAU7802 in your board .overlay like this example:

/{	
    force_sens_1: nau7802_loadcell@2A {
        // label = "NAU7802_1";
        compatible = "nuvoton,nau7802_loadcell";
        reg = <0x2A>;
        drdy-gpios = <&gpiod 1 GPIO_ACTIVE_HIGH>;
        conversions-per-second = <320>; //SPS
        gain = <128>;
    };
};

Driver usage

#include <zephyr/drivers/gpio.h>
#include <zephyr/drivers/sensor.h>
#include <zephyr/drivers/i2c.h>
#include <zephyr/logging/log.h>
/* this is for getting the SENSOR_CHAN_FORCE*/
#include "../../../modules/nau7802_loadcell/drivers/sensor/nau7802_loadcell/nau7802_loadcell.h"

/* Declare the membership in registered logging module*/
LOG_MODULE_REGISTER(LOADCELL_TEST, CONFIG_SENSOR_LOG_LEVEL);

static int process_sensor_value(const struct device *dev)
{
	struct sensor_value force;
	int ret;

	ret = sensor_sample_fetch(dev);
	if (ret != 0) {
		LOG_ERR("ret: %d, Sensor sample update error", ret);
		return ret;
	}

	ret = sensor_channel_get(dev, SENSOR_CHAN_FORCE, &force);
	if (ret != 0) {
		LOG_ERR("ret: %d, Cannot read NAU7802 force channelr", ret);
		return ret;
	}

	LOG_INF("Force:%f", sensor_value_to_double(&force));
	return 0;
}

static void nau7802_loadcell_handler(const struct device *dev,
			   const struct sensor_trigger *trig)
{
	process_sensor_value(dev);
}

void test_loadcell(void)
{
    /* Get the device pointer to nau7802 sensor*/
	const struct device *const nau7802 = DEVICE_DT_GET_ONE(nuvoton_nau7802_loadcell);

	if (!device_is_ready(nau7802)) {
		LOG_ERR("sensor: device not ready.");
		return;
	}

	/* set the offset and calibration factor*/
	float32_t offset = 2.505000511475965652e+01;
	float32_t calibFactor = 6.527824679590503775e-06;
	const struct sensor_value offset_attri;
	const struct sensor_value calib_attri;

	/* Currently don't have a good way to pass floating point value to the sensor driver*/
	/* Use the memcpy to do bit-to-bit copy, from float32_t to int32_t*/
	memcpy(&offset_attri.val1, &offset, sizeof(offset));
	memcpy(&calib_attri.val1, &calibFactor, sizeof(calibFactor));

	if(sensor_attr_set(nau7802, SENSOR_CHAN_FORCE, SENSOR_ATTR_OFFSET, &offset_attri) != 0){
		LOG_ERR("Cannot configure the offset");
		return;
	}

	if(sensor_attr_set(nau7802, SENSOR_CHAN_FORCE, SENSOR_ATTR_CALIBRATION, &calib_attri) != 0){
		LOG_ERR("Cannot configure the offset");
		return;
	}

	/* Set the tragger type and handler function if needed*/
	if (IS_ENABLED(CONFIG_NAU7802_LOADCELL_TRIGGER)) {
		struct sensor_trigger trig = {
			.type = SENSOR_TRIG_DATA_READY,
			.chan = SENSOR_CHAN_ALL,
		};
		if (sensor_trigger_set(nau7802, &trig, nau7802_loadcell_handler) < 0) {
			LOG_ERR("Cannot configure trigger");
			return;
		}
	}
	
	while (!IS_ENABLED(CONFIG_NAU7802_LOADCELL_TRIGGER)) {
		process_sensor_value(nau7802);
		k_sleep(K_MSEC(2000));
	}
	k_sleep(K_FOREVER);


}

Relevant prj.conf:

CONFIG_SENSOR=y
CONFIG_NAU7802_LOADCELL=y
CONFIG_NAU7802_LOADCELL_TRIGGER_GLOABL_THREAD=y
CONFIG_LOG=y