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Step 03 — Telemetry: publish sensor data

After this step the ESP32 will read temperature and humidity from an SHT31 sensor and publish the values to the portal every 10 seconds. The portal will display them as a live graph.

What you need

Hardware:

  • SHT31 on an I2C breakout module (address 0x44 or 0x45)
  • Wires: SDA, SCL, VCC (3.3 V), GND

Software:

  • PlatformIO
  • Library robtillaart/SHT31 @ ^0.5.0

Steps

1. Connect SHT31 to ESP32-C3 (default pins used by Storage Link):

SHT31 ESP32-C3
VCC 3.3 V
GND GND
SDA GPIO 8
SCL GPIO 9

Warning

Connect the sensor only with the board powered off.

2. Add the library to platformio.ini:

lib_deps =
    robtillaart/SHT31 @ ^0.5.0
    ; ... other dependencies

3. Include Wire and the sensor in main.cpp. Based on iDryer-Storage/src/main.cpp:

#include <Wire.h>
#include "storage/sensors/Sht31ClimateSensor.h"

static Sht31ClimateSensor s_sensor(&Wire);
static bool s_sensorOk = false;

4. Initialise in setup():

Wire.begin(8, 9);  // SDA=8, SCL=9
s_sensorOk = s_sensor.begin();  // auto-detects address 0x44 or 0x45

begin() returns false if no sensor is found. The device will continue running without it.

5. Call tick() in loop() and update the telemetry fields:

if (s_sensorOk) {
    s_sensor.tick(millis());
    SensorReading r = s_sensor.get();
    if (r.ok) {
        s_link.telemetry.airTempC[0]       = r.temperature;
        s_link.telemetry.airHumidityPct[0] = r.humidity;
    }
}

The library publishes all telemetry.* fields to MQTT automatically at the interval set by telemetryPeriodMs in iDryer::Config. The default is 10 000 ms.

6. Enable the capability in iDryer::Config:

static const iDryer::Config CFG = {
    // ...
    .hasAirTemp     = true,
    .hasAirHumidity = true,
    .telemetryPeriodMs = 10000,
};

Verification

Open the Serial Monitor. On successful sensor detection:

[MAIN] SHT31 at 0x44

On the portal, navigate to the device page — temperature and humidity readings update every 10 seconds.

If the sensor is not found a warning is logged and the device continues running. Check that address 0x44/0x45 is not occupied by another device on the bus.

What's next