Initial Commit

src/main.c

@@ -0,0 +1,120 @@
+/*
+ * BTHome v2 temperature / humidity beacon - ultra-low-power (Zephyr)
+ *
+ * Every 60 s: power up SHT41, measure T/RH, power it down, read VDDH,
+ * update a non-connectable BTHome v2 advertisement sent every 10 s.
+ * Sensor power gating, I2C pin handling, DC/DC and sleep are all
+ * configured in app.overlay / prj.conf.
+ */
+#include <zephyr/kernel.h>
+#include <zephyr/bluetooth/bluetooth.h>
+#include <zephyr/drivers/adc.h>
+#include <zephyr/drivers/sensor.h>
+#include <zephyr/pm/device_runtime.h>
+#include <zephyr/sys/byteorder.h>
+
+#define MEAS_INTERVAL K_SECONDS(60)
+#define ADV_INTERVAL  16000 /* 10000 ms / 0.625 ms (legacy max is 10.24 s) */
+#define VDDH_DIV      5     /* SAADC input is VDDH/5 */
+
+static const struct device *const sht = DEVICE_DT_GET(DT_NODELABEL(sht41));
+static const struct adc_dt_spec vbat = ADC_DT_SPEC_GET(DT_PATH(zephyr_user));
+
+/* BTHome v2 service data (objects in ascending ID order: 0x0C, 0x2E, 0x45) */
+static uint8_t svc[] = {
+	0xD2, 0xFC, /* UUID 0xFCD2 */
+	0x40,       /* BTHome v2, unencrypted, regular interval */
+	0x0C, 0, 0, /* voltage, 1 mV */
+	0x2E, 0,    /* humidity, 1 % */
+	0x45, 0, 0, /* temperature, 0.1 degC */
+};
+
+static const struct bt_data ad[] = {
+	BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR),
+	BT_DATA(BT_DATA_SVC_DATA16, svc, sizeof(svc)),
+	BT_DATA(BT_DATA_NAME_COMPLETE, CONFIG_BT_DEVICE_NAME, sizeof(CONFIG_BT_DEVICE_NAME) - 1),
+};
+
+static int read_sht41(void)
+{
+	struct sensor_value t, rh;
+	int err = pm_device_runtime_get(sht); /* sensor power on */
+
+	if (err) {
+		return err;
+	}
+	err = sensor_sample_fetch(sht);
+	pm_device_runtime_put(sht);           /* bus high-Z, then sensor power off */
+	if (err) {
+		return err;
+	}
+
+	sensor_channel_get(sht, SENSOR_CHAN_AMBIENT_TEMP, &t);
+	sensor_channel_get(sht, SENSOR_CHAN_HUMIDITY, &rh);
+
+	int32_t mc = sensor_value_to_milli(&t);
+	int16_t t10 = (mc + (mc < 0 ? -50 : 50)) / 100;
+	int32_t pct = (sensor_value_to_milli(&rh) + 500) / 1000;
+
+	sys_put_le16(t10, &svc[9]);
+	svc[7] = CLAMP(pct, 0, 100);
+	return 0;
+}
+
+static void read_battery(void)
+{
+	static bool calibrated;
+	int16_t raw;
+	struct adc_sequence seq = {
+		.buffer = &raw,
+		.buffer_size = sizeof(raw),
+		.calibrate = !calibrated,
+	};
+
+	adc_sequence_init_dt(&vbat, &seq);
+	if (adc_read_dt(&vbat, &seq) == 0) {
+		/* Full-scale input voltage: 0.6 V ref / gain 1/2 = 1200 mV */
+		int32_t full_mv = adc_ref_internal(vbat.dev);
+
+		adc_gain_invert(vbat.channel_cfg.gain, &full_mv);
+
+		/*
+		 * Scale raw straight to VDDH in one step and round to nearest:
+		 * VDDH_mV = raw * 1200 * 5 / 2^res. Multiplying by 5 before the
+		 * division keeps 1 mV resolution instead of 5 mV steps.
+		 * Max 16383 * 1200 * 5 = 98 M, fits in 32 bits.
+		 */
+		uint32_t num = (uint32_t)MAX(raw, 0) * (uint32_t)full_mv * VDDH_DIV;
+		uint32_t mv = (num + BIT(vbat.resolution - 1)) >> vbat.resolution;
+
+		sys_put_le16(mv, &svc[4]);
+		calibrated = true;
+	}
+}
+
+static bool measure(void)
+{
+	if (read_sht41()) {
+		return false;   /* keep advertising last good values */
+	}
+	read_battery();         /* right after sensor load */
+	return true;
+}
+
+int main(void)
+{
+	adc_channel_setup_dt(&vbat);
+	bt_enable(NULL);
+	measure();              /* advertise even if the first read fails */
+
+	bt_le_adv_start(BT_LE_ADV_PARAM(BT_LE_ADV_OPT_USE_IDENTITY, ADV_INTERVAL,
+					ADV_INTERVAL, NULL),
+			ad, ARRAY_SIZE(ad), NULL, 0);
+
+	for (;;) {
+		k_sleep(MEAS_INTERVAL); /* CPU in System ON idle */
+		if (measure()) {
+			bt_le_adv_update_data(ad, ARRAY_SIZE(ad), NULL, 0);
+		}
+	}
+}