【ST NUCLEO-C031C6开发板测评】I2C获取温湿度传感器SHT30数据
<div class='showpostmsg'><p><strong>一、硬件了解</strong></p><p>从手册可以得知，PB8、PB9可以用作I2C1接口：</p>
<p> </p>
<p>对应开发板上，可以用如下位置的接口：</p>
<p> </p>
<p> </p>
<p><strong>二、SHT30温湿度传感器</strong></p>
<p>我手头有一个标准的最简化的SHT30温湿度传感器，具体如下：</p>
<p> </p>
<p>这个SHT30用3.3V供电，I2C接口通讯。</p>
<p> </p>
<p>连接到开发板：</p>
<p> </p>
<p><strong>三、zephyr配置</strong></p>
<p>在 zephyr中，有一个示例samples/sensor/sht3xd，展示了从sht3xd读取数据，要在STM32C0的开发板上使用，需要做一些配置。</p>
<p> </p>
<p>首先，从zephyr/boards/arm/nucleo_c031c6/nucleo_c031c6.dts中，查看i2c的dts配置：</p>
<pre>
<code class="language-javascript">&i2c1 {
pinctrl-0 = <&i2c1_scl_pb8 &i2c1_sda_pb9>;
pinctrl-names = "default";
status = "okay";
clock-frequency = <I2C_BITRATE_FAST>;
};</code></pre>
<p>从上述配置，可以看到，i2c使用了pb8、pb9。</p>
<p>另外，配置中定义了i2c通讯速率I2C_BITRATE_FAST，其具体的定义在 zephyr/include/zephyr/dt-bindings/i2c/i2c.h 文件中：</p>
<pre>
<code class="language-json">#define I2C_BITRATE_STANDARD 100000/* 100 Kbit/s */
#define I2C_BITRATE_FAST 400000/* 400 Kbit/s */
#define I2C_BITRATE_FAST_PLUS 1000000 /* 1 Mbit/s */
#define I2C_BITRATE_HIGH 3400000 /* 3.4 Mbit/s */
#define I2C_BITRATE_ULTRA 5000000 /* 5 Mbit/s */</code></pre>
<p>所以，对应的速率为400 Kbits/s。</p>
<p> </p>
<p>另外，还需要编写 zephyr/samples/sensor/sht3xd/boards/nucleo_c031c6.overlay，用于定义sht3xd传感器：</p>
<pre>
<code class="language-cpp">&i2c1 { /* SDA CN5.9=PB9, SCL CN5.10=PB8, ALERT CN5.1=D8=PA9 */
/* &i2c3 { * SDA CN7.36=PC1, SCL CN7.38=PC0, ALERT CN7.34=PB0 */
sht3xd@44 {
compatible = "sensirion,sht3xd";
reg = <0x44>;
};
};</code></pre>
<p>上述配置中，设置了传感器的具体类型，对应：zephyr/dts/bindings/sensor/sensirion,sht3xd.yaml</p>
<pre>
<code class="language-ini"># Copyright (c) 2018, Peter Bigot Consulting, LLC
# SPDX-License-Identifier: Apache-2.0
description: Sensirion Humidity SHT3x-DIS humidity and temperature sensor
compatible: "sensirion,sht3xd"
include:
properties:
alert-gpios:
type: phandle-array
description: |
ALERT pin.
This pin signals active high when produced by the sensor.The
property value should ensure the flags properly describe the
signal that is presented to the driver.</code></pre>
<p>其对应的驱动位置：./drivers/sensor/sht3xd</p>
<pre>
<code class="language-bash">./drivers/sensor/sht3xd
├── CMakeLists.txt
├── Kconfig
├── sht3xd.c
├── sht3xd.h
└── sht3xd_trigger.c</code></pre>
<p>做完上述配置，就可以编写具体程序了。</p>
<p> </p>
<p><strong>四、代码编写</strong></p>
<p>参考 samples/sensor/sht3xd/src/main.c，编写如下的代码：</p>
<pre>
<code class="language-cpp">#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/drivers/sensor.h>
#include <stdio.h>
const struct device *const dev = DEVICE_DT_GET_ONE(sensirion_sht3xd);
int main(void)
{
int rc;
if (!device_is_ready(dev)) {
printf("Device %s is not ready\n", dev->name);
return 0;
}
while (true) {
struct sensor_value temp, hum;
rc = sensor_sample_fetch(dev);
if (rc == 0) {
rc = sensor_channel_get(dev, SENSOR_CHAN_AMBIENT_TEMP,
&temp);
}
if (rc == 0) {
rc = sensor_channel_get(dev, SENSOR_CHAN_HUMIDITY,
&hum);
}
if (rc != 0) {
printf("SHT3XD: failed: %d\n", rc);
break;
}
printf("SHT3XD: %d.%d=%.2f Cel ; %d.%d=%0.2f %%RH\n",
temp.val1,temp.val2,
sensor_value_to_double(&temp),
hum.val1,hum.val2,
sensor_value_to_double(&hum));
k_sleep(K_MSEC(2000));
}
return 0;
}
</code></pre>
<p>在上述代码中，通过别名 sensirion_sht3xd 来获得dts配置的设备，然后通过device_is_ready()检查设备是否准备去就绪。</p>
<p>因为前面做了dts配置，所以一旦系统启动，就会自动做好准备，提供服务。</p>
<p> </p>
<p>然后，调用sensor_sample_fetch()进行数据采样，采样后，就可以调用sensor_channel_get()来获取数据了。</p>
<p>在 zephyr/include/zephyr/drivers/sensor.h 中，定义了传感器数据读取的结构，以及对应的数据通道：</p>
<pre>
<code class="language-cpp">struct sensor_value {
int32_t val1;
int32_t val2;
};
enum sensor_channel {
SENSOR_CHAN_ACCEL_X,
SENSOR_CHAN_ACCEL_Y,
SENSOR_CHAN_ACCEL_Z,
SENSOR_CHAN_ACCEL_XYZ,
SENSOR_CHAN_GYRO_X,
SENSOR_CHAN_GYRO_Y,
SENSOR_CHAN_GYRO_Z,
SENSOR_CHAN_GYRO_XYZ,
SENSOR_CHAN_MAGN_X,
SENSOR_CHAN_MAGN_Y,
SENSOR_CHAN_MAGN_Z,
SENSOR_CHAN_MAGN_XYZ,
SENSOR_CHAN_DIE_TEMP,
SENSOR_CHAN_AMBIENT_TEMP,
SENSOR_CHAN_PRESS,
SENSOR_CHAN_PROX,
SENSOR_CHAN_HUMIDITY,
SENSOR_CHAN_LIGHT,
SENSOR_CHAN_IR,
SENSOR_CHAN_RED,
SENSOR_CHAN_GREEN,
SENSOR_CHAN_BLUE,
SENSOR_CHAN_ALTITUDE,
SENSOR_CHAN_PM_1_0,
SENSOR_CHAN_PM_2_5,
SENSOR_CHAN_PM_10,
SENSOR_CHAN_DISTANCE,
SENSOR_CHAN_CO2,
SENSOR_CHAN_VOC,
SENSOR_CHAN_GAS_RES,
SENSOR_CHAN_VOLTAGE,
SENSOR_CHAN_VSHUNT,
SENSOR_CHAN_CURRENT,
SENSOR_CHAN_POWER,
SENSOR_CHAN_RESISTANCE,
SENSOR_CHAN_ROTATION,
SENSOR_CHAN_POS_DX,
SENSOR_CHAN_POS_DY,
SENSOR_CHAN_POS_DZ,
SENSOR_CHAN_RPM,
SENSOR_CHAN_GAUGE_VOLTAGE,
SENSOR_CHAN_GAUGE_AVG_CURRENT,
SENSOR_CHAN_GAUGE_STDBY_CURRENT,
SENSOR_CHAN_GAUGE_MAX_LOAD_CURRENT,
SENSOR_CHAN_GAUGE_TEMP,
SENSOR_CHAN_GAUGE_STATE_OF_CHARGE,
SENSOR_CHAN_GAUGE_FULL_CHARGE_CAPACITY,
SENSOR_CHAN_GAUGE_REMAINING_CHARGE_CAPACITY,
SENSOR_CHAN_GAUGE_NOM_AVAIL_CAPACITY,
SENSOR_CHAN_GAUGE_FULL_AVAIL_CAPACITY,
SENSOR_CHAN_GAUGE_AVG_POWER,
SENSOR_CHAN_GAUGE_STATE_OF_HEALTH,
SENSOR_CHAN_GAUGE_TIME_TO_EMPTY,
SENSOR_CHAN_GAUGE_TIME_TO_FULL,
SENSOR_CHAN_GAUGE_CYCLE_COUNT,
SENSOR_CHAN_GAUGE_DESIGN_VOLTAGE,
SENSOR_CHAN_GAUGE_DESIRED_VOLTAGE,
SENSOR_CHAN_GAUGE_DESIRED_CHARGING_CURRENT,
SENSOR_CHAN_ALL,
SENSOR_CHAN_COMMON_COUNT,
SENSOR_CHAN_PRIV_START = SENSOR_CHAN_COMMON_COUNT,
SENSOR_CHAN_MAX = INT16_MAX,
};</code></pre>
<p>温度对应的通道为 SENSOR_CHAN_AMBIENT_TEMP，湿度对应的通道为SENSOR_CHAN_HUMIDITY，所以读取温湿度信息，使用如下代码：</p>
<pre>
<code class="language-cpp"> rc = sensor_sample_fetch(dev);
if (rc == 0) {
rc = sensor_channel_get(dev, SENSOR_CHAN_AMBIENT_TEMP,
&temp);
}
if (rc == 0) {
rc = sensor_channel_get(dev, SENSOR_CHAN_HUMIDITY,
&hum);
}</code></pre>
<p>数据读取成功后，可以调用 sensor_value_to_double()将结构化数据转换为double浮点数据。</p>
<p> </p>
<p><strong>五、输出结果</strong></p>
<p>将上述代码编译下载到开发板，运行后，即可输出温湿度信息：</p>
<p> </p>
<p> </p>
<p>用手捏住SHT30的传感器部分，温度就会上升。</p>
<p>对着它哈气，湿度就会上升了。</p>
<p> </p>
<p> </p>
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捏住传感器会不会污染传感器，影响后期传感器检测精度
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<p>这个zephyr和linux一样的开发路线了，用起来应该很熟悉</p>
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