Add SHT21 sensor support

src/configuration.h

@@ -219,6 +219,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define LPS22HB_ADDR_ALT 0x5D
 #define SHT31_4x_ADDR 0x44
 #define SHT31_4x_ADDR_ALT 0x45
+#define SHT21_ADDR 0x40 // same address as INA_ADDR
+#ifndef HAS_SHT21
+#define HAS_SHT21 0 // set to one to override detection of INA219/260 devices at this address
+#endif
 #define PMSA003I_ADDR 0x12
 #define QMA6100P_ADDR 0x12
 #define AHT10_ADDR 0x38

src/detect/ScanI2C.h

@@ -32,6 +32,7 @@ class ScanI2C
         MAX17048,
         MCP9808,
         SHT31,
+        SHT21,
         SHT4X,
         SHTC3,
         LPS22HB,

src/detect/ScanI2CTwoWire.cpp

@@ -308,7 +308,9 @@ void ScanI2CTwoWire::scanPort(I2CPort port, uint8_t *address, uint8_t asize)
                 break;
 #endif
 #if !defined(M5STACK_UNITC6L)
+#if !HAS_SHT21
             case INA_ADDR:
+#endif
             case INA_ADDR_ALTERNATE:
             case INA_ADDR_WAVESHARE_UPS:
                 registerValue = getRegisterValue(ScanI2CTwoWire::RegisterLocation(addr, 0xFE), 2);
@@ -401,6 +403,14 @@ void ScanI2CTwoWire::scanPort(I2CPort port, uint8_t *address, uint8_t asize)
 
                 break;
 
+#if HAS_SHT21
+            case SHT21_ADDR:
+                // SHT21 / HTU21D family commonly at 0x40
+                logFoundDevice("SHT21/HTU21D", (uint8_t)addr.address);
+                type = SHT21;
+                break;
+#endif
+
                 SCAN_SIMPLE_CASE(SHTC3_ADDR, SHTC3, "SHTC3", (uint8_t)addr.address)
             case RCWL9620_ADDR:
                 // get MAX30102 PARTID

src/mesh/generated/meshtastic/telemetry.pb.h

@@ -103,7 +103,9 @@ typedef enum _meshtastic_TelemetrySensorType {
     /* TSL2561 light sensor */
     meshtastic_TelemetrySensorType_TSL2561 = 44,
     /* BH1750 light sensor */
-    meshtastic_TelemetrySensorType_BH1750 = 45
+    meshtastic_TelemetrySensorType_BH1750 = 45,
+    /* STH21 Temperature and R. Humidity sensor */
+    meshtastic_TelemetrySensorType_SHT21 = 46
 } meshtastic_TelemetrySensorType;
 
 /* Struct definitions */
@@ -461,8 +463,8 @@ extern "C" {
 
 /* Helper constants for enums */
 #define _meshtastic_TelemetrySensorType_MIN meshtastic_TelemetrySensorType_SENSOR_UNSET
-#define _meshtastic_TelemetrySensorType_MAX meshtastic_TelemetrySensorType_BH1750
-#define _meshtastic_TelemetrySensorType_ARRAYSIZE ((meshtastic_TelemetrySensorType)(meshtastic_TelemetrySensorType_BH1750+1))
+#define _meshtastic_TelemetrySensorType_MAX meshtastic_TelemetrySensorType_SHT21
+#define _meshtastic_TelemetrySensorType_ARRAYSIZE ((meshtastic_TelemetrySensorType)(meshtastic_TelemetrySensorType_SHT21+1))
 
 
 

src/modules/Telemetry/EnvironmentTelemetry.cpp

@@ -69,6 +69,10 @@ extern void drawCommonHeader(OLEDDisplay *display, int16_t x, int16_t y, const c
 #include "Sensor/SHT31Sensor.h"
 #endif
 
+#if HAS_SHT21
+#include "Sensor/SHT21Sensor.h"
+#endif
+
 #if __has_include(<Adafruit_LPS2X.h>)
 #include "Sensor/LPS22HBSensor.h"
 #endif
@@ -202,6 +206,9 @@ void EnvironmentTelemetryModule::i2cScanFinished(ScanI2C *i2cScanner)
 #if __has_include(<Adafruit_SHT31.h>)
     addSensor<SHT31Sensor>(i2cScanner, ScanI2C::DeviceType::SHT31);
 #endif
+#if HAS_SHT21
+    addSensor<SHT21Sensor>(i2cScanner, ScanI2C::DeviceType::SHT21);
+#endif
 #if __has_include(<Adafruit_LPS2X.h>)
     addSensor<LPS22HBSensor>(i2cScanner, ScanI2C::DeviceType::LPS22HB);
 #endif

src/modules/Telemetry/Sensor/SHT21Sensor.cpp

@@ -0,0 +1,85 @@
+#include "configuration.h"
+
+#if !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR
+
+#include "SHT21Sensor.h"
+#include "../mesh/generated/meshtastic/telemetry.pb.h"
+#include "TelemetrySensor.h"
+#include <Wire.h>
+#include <cmath>
+
+// SHT21 I2C address and commands (use no-hold commands to avoid clock-stretch issues)
+static const uint8_t CMD_TEMP_NOHOLD = 0xF3;
+static const uint8_t CMD_HUM_NOHOLD = 0xF5;
+
+static bool read_sht21_raw(TwoWire *bus, uint8_t addr, uint8_t cmd, uint16_t &raw, uint16_t waitMs)
+{
+    bus->beginTransmission(addr);
+    bus->write(cmd);
+    if (bus->endTransmission() != 0)
+        return false;
+    // Wait for measurement to complete (no-hold mode)
+    delay(waitMs);
+    int toRead = 3; // two data bytes + CRC
+    bus->requestFrom((int)addr, toRead);
+    if (bus->available() < 2)
+        return false;
+    uint8_t msb = bus->read();
+    uint8_t lsb = bus->read();
+    if (bus->available())
+        (void)bus->read();
+
+    raw = ((uint16_t)msb << 8) | lsb;
+    // clear status bits per datasheet
+    raw &= ~0x0003;
+    return true;
+}
+
+SHT21Sensor::SHT21Sensor() : TelemetrySensor(meshtastic_TelemetrySensorType_SHT21, "SHT21") {}
+
+bool SHT21Sensor::initDevice(TwoWire *bus, ScanI2C::FoundDevice *dev)
+{
+    LOG_INFO("Init sensor: %s", sensorName);
+    i2c = bus;
+    i2c_addr = dev->address.address ? dev->address.address : SHT21_ADDR;
+
+    uint16_t raw;
+    // use no-hold command and wait for conversion (max ~85ms for temp)
+    if (!read_sht21_raw(i2c, i2c_addr, CMD_TEMP_NOHOLD, raw, 85)) {
+        return false;
+    }
+    float temp = -46.85f + 175.72f * ((float)raw / 65536.0f);
+    // basic sanity check
+    if (temp < -50.0f || temp > 150.0f)
+        return false;
+
+    status = true;
+    initI2CSensor();
+    return true;
+}
+
+bool SHT21Sensor::getMetrics(meshtastic_Telemetry *measurement)
+{
+    measurement->variant.environment_metrics.has_temperature = true;
+    measurement->variant.environment_metrics.has_relative_humidity = true;
+
+    LOG_DEBUG("SHT21 getMetrics");
+
+    uint16_t raw_t = 0, raw_h = 0;
+    if (!read_sht21_raw(i2c, i2c_addr, CMD_TEMP_NOHOLD, raw_t, 85))
+        return false;
+    // humidity max conversion time ~29ms
+    if (!read_sht21_raw(i2c, i2c_addr, CMD_HUM_NOHOLD, raw_h, 30))
+        return false;
+
+    float temp = -46.85f + 175.72f * ((float)raw_t / 65536.0f);
+    float rh = -6.0f + 125.0f * ((float)raw_h / 65536.0f);
+
+    // Round to 2 decimal places for telemetry
+    measurement->variant.environment_metrics.temperature = roundf(temp * 100.0f) / 100.0f;
+    measurement->variant.environment_metrics.relative_humidity = roundf(rh * 100.0f) / 100.0f;
+
+    return true;
+}
+
+#endif

src/modules/Telemetry/Sensor/SHT21Sensor.h

@@ -0,0 +1,22 @@
+#include "configuration.h"
+
+#if !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR
+
+#include "../mesh/generated/meshtastic/telemetry.pb.h"
+#include "TelemetrySensor.h"
+#include <Wire.h>
+
+class SHT21Sensor : public TelemetrySensor
+{
+  private:
+    TwoWire *i2c = nullptr;
+    uint8_t i2c_addr = 0;
+    bool status = false;
+
+  public:
+    SHT21Sensor();
+    virtual bool getMetrics(meshtastic_Telemetry *measurement) override;
+    virtual bool initDevice(TwoWire *bus, ScanI2C::FoundDevice *dev) override;
+};
+
+#endif