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build/
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(nRF52840-SHT41-BTHome-NCS)
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target_sources(app PRIVATE src/main.c)
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/* Pro Micro nRF52840 (nice!nano v2 compatible) + Adafruit SHT41 on a gated supply */
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#include <zephyr/dt-bindings/adc/adc.h>
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#include <zephyr/dt-bindings/adc/nrf-saadc.h>
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#include <zephyr/dt-bindings/gpio/nordic-nrf-gpio.h>
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/ {
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/* P0.17 powers the SHT41: switched on only while the sensor is in use */
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sens_pwr: sensor-power {
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compatible = "power-domain-gpio";
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enable-gpios = <&gpio0 17 (GPIO_ACTIVE_HIGH | NRF_GPIO_DRIVE_H0H1)>;
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startup-delay-us = <3000>; /* SHT41 power-up + breakout caps */
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#power-domain-cells = <0>;
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zephyr,pm-device-runtime-auto;
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};
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zephyr,user {
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io-channels = <&adc 0>;
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};
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};
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/* DC/DC on REG0 (VDDH -> VDD) and REG1 (VDD -> core) */
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®0 {
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status = "okay";
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};
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®1 {
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regulator-initial-mode = <NRF5X_REG_MODE_DCDC>;
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};
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/* I2C: SDA P0.20, SCL P0.22. "sleep" state = pins disconnected (no back-feeding) */
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&pinctrl {
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sht_i2c_default: sht_i2c_default {
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group1 {
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psels = <NRF_PSEL(TWIM_SDA, 0, 20)>, <NRF_PSEL(TWIM_SCL, 0, 22)>;
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bias-pull-up;
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};
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};
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sht_i2c_sleep: sht_i2c_sleep {
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group1 {
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psels = <NRF_PSEL(TWIM_SDA, 0, 20)>, <NRF_PSEL(TWIM_SCL, 0, 22)>;
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low-power-enable;
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};
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};
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};
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&i2c0 {
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compatible = "nordic,nrf-twim";
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status = "okay";
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clock-frequency = <I2C_BITRATE_FAST>;
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pinctrl-0 = <&sht_i2c_default>;
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pinctrl-1 = <&sht_i2c_sleep>;
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pinctrl-names = "default", "sleep";
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zephyr,pm-device-runtime-auto; /* bus enabled only during transfers */
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sht41: sht4x@44 {
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compatible = "sensirion,sht4x";
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reg = <0x44>;
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repeatability = <2>; /* high precision, no heater */
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power-domains = <&sens_pwr>;
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zephyr,pm-device-runtime-auto;
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};
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};
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/* Battery: VDDH/5, internal 0.6 V ref, gain 1/2 -> 0..1.2 V range */
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&adc {
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#address-cells = <1>;
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#size-cells = <0>;
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status = "okay";
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channel@0 {
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reg = <0>;
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zephyr,gain = "ADC_GAIN_1_2";
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zephyr,reference = "ADC_REF_INTERNAL";
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zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)>;
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zephyr,input-positive = <NRF_SAADC_VDDHDIV5>;
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zephyr,resolution = <14>; /* LSB = 6000 mV / 16384 = 0.37 mV at VDDH */
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zephyr,oversampling = <3>; /* 2^3 = 8x */
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};
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};
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/* Unused board peripherals */
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&i2c1 { status = "disabled"; };
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&spi2 { status = "disabled"; };
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&pwm0 { status = "disabled"; };
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&uart0 { status = "disabled"; };
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&usbd { status = "disabled"; };
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# Bluetooth: advertising only
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CONFIG_BT=y
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CONFIG_BT_BROADCASTER=y
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CONFIG_BT_DEVICE_NAME="SHT41"
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CONFIG_BT_CTLR_TX_PWR_0=y
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# Drivers
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CONFIG_I2C=y
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CONFIG_SENSOR=y
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CONFIG_ADC=y
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# Power management: sensor + I2C bus powered only while in use
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CONFIG_PM_DEVICE=y
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CONFIG_PM_DEVICE_RUNTIME=y
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CONFIG_POWER_DOMAIN=y
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# Board enables USB serial console by default: turn it all off
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CONFIG_USB_DEVICE_STACK_NEXT=n
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CONFIG_SERIAL=n
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CONFIG_CONSOLE=n
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CONFIG_UART_CONSOLE=n
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CONFIG_LOG=n
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/*
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* BTHome v2 temperature / humidity beacon - ultra-low-power (Zephyr)
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*
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* Every 60 s: power up SHT41, measure T/RH, power it down, read VDDH,
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* update a non-connectable BTHome v2 advertisement sent every 10 s.
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* Sensor power gating, I2C pin handling, DC/DC and sleep are all
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* configured in app.overlay / prj.conf.
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/bluetooth/bluetooth.h>
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#include <zephyr/drivers/adc.h>
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#include <zephyr/drivers/sensor.h>
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#include <zephyr/pm/device_runtime.h>
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#include <zephyr/sys/byteorder.h>
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#define MEAS_INTERVAL K_SECONDS(60)
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#define ADV_INTERVAL 16000 /* 10000 ms / 0.625 ms (legacy max is 10.24 s) */
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#define VDDH_DIV 5 /* SAADC input is VDDH/5 */
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static const struct device *const sht = DEVICE_DT_GET(DT_NODELABEL(sht41));
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static const struct adc_dt_spec vbat = ADC_DT_SPEC_GET(DT_PATH(zephyr_user));
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/* BTHome v2 service data (objects in ascending ID order: 0x0C, 0x2E, 0x45) */
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static uint8_t svc[] = {
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0xD2, 0xFC, /* UUID 0xFCD2 */
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0x40, /* BTHome v2, unencrypted, regular interval */
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0x0C, 0, 0, /* voltage, 1 mV */
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0x2E, 0, /* humidity, 1 % */
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0x45, 0, 0, /* temperature, 0.1 degC */
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};
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static const struct bt_data ad[] = {
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BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR),
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BT_DATA(BT_DATA_SVC_DATA16, svc, sizeof(svc)),
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BT_DATA(BT_DATA_NAME_COMPLETE, CONFIG_BT_DEVICE_NAME, sizeof(CONFIG_BT_DEVICE_NAME) - 1),
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};
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static int read_sht41(void)
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{
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struct sensor_value t, rh;
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int err = pm_device_runtime_get(sht); /* sensor power on */
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if (err) {
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return err;
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}
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err = sensor_sample_fetch(sht);
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pm_device_runtime_put(sht); /* bus high-Z, then sensor power off */
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if (err) {
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return err;
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}
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sensor_channel_get(sht, SENSOR_CHAN_AMBIENT_TEMP, &t);
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sensor_channel_get(sht, SENSOR_CHAN_HUMIDITY, &rh);
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int32_t mc = sensor_value_to_milli(&t);
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int16_t t10 = (mc + (mc < 0 ? -50 : 50)) / 100;
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int32_t pct = (sensor_value_to_milli(&rh) + 500) / 1000;
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sys_put_le16(t10, &svc[9]);
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svc[7] = CLAMP(pct, 0, 100);
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return 0;
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}
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static void read_battery(void)
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{
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static bool calibrated;
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int16_t raw;
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struct adc_sequence seq = {
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.buffer = &raw,
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.buffer_size = sizeof(raw),
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.calibrate = !calibrated,
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};
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adc_sequence_init_dt(&vbat, &seq);
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if (adc_read_dt(&vbat, &seq) == 0) {
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/* Full-scale input voltage: 0.6 V ref / gain 1/2 = 1200 mV */
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int32_t full_mv = adc_ref_internal(vbat.dev);
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adc_gain_invert(vbat.channel_cfg.gain, &full_mv);
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/*
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* Scale raw straight to VDDH in one step and round to nearest:
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* VDDH_mV = raw * 1200 * 5 / 2^res. Multiplying by 5 before the
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* division keeps 1 mV resolution instead of 5 mV steps.
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* Max 16383 * 1200 * 5 = 98 M, fits in 32 bits.
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*/
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uint32_t num = (uint32_t)MAX(raw, 0) * (uint32_t)full_mv * VDDH_DIV;
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uint32_t mv = (num + BIT(vbat.resolution - 1)) >> vbat.resolution;
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sys_put_le16(mv, &svc[4]);
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calibrated = true;
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}
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}
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static bool measure(void)
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{
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if (read_sht41()) {
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return false; /* keep advertising last good values */
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}
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read_battery(); /* right after sensor load */
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return true;
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}
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int main(void)
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{
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adc_channel_setup_dt(&vbat);
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bt_enable(NULL);
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measure(); /* advertise even if the first read fails */
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bt_le_adv_start(BT_LE_ADV_PARAM(BT_LE_ADV_OPT_USE_IDENTITY, ADV_INTERVAL,
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ADV_INTERVAL, NULL),
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ad, ARRAY_SIZE(ad), NULL, 0);
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for (;;) {
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k_sleep(MEAS_INTERVAL); /* CPU in System ON idle */
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if (measure()) {
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bt_le_adv_update_data(ad, ARRAY_SIZE(ad), NULL, 0);
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}
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}
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}
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