Sensors

On this page you connect two sensors and output their data to the portal. First the SHT31 (cabinet climate), then the thermistor (heater temperature). This is the "read data" step before adding control logic.

The principle of working with the core is simple: your code in loop() writes fresh readings to s_link.telemetry.* fields, and the facade publishes them to the cloud every telemetryPeriodMs from Config. You do not need to call publish manually.

Telemetry fields

For our cabinet, three fields are used (index [0] — the first and only chamber):

Field	What it stores	Flag in Config
s_link.telemetry.airTempC[0]	air temperature, °C	hasAirTemp
s_link.telemetry.airHumidityPct[0]	air humidity, %	hasAirHumidity
s_link.telemetry.heaterTempC[0]	heater temperature, °C	hasHeaterTemp

We have already enabled all three flags in the Config in the previous step.

Rule: sensor code must not block loop()

The idryer-core facade services Wi-Fi and MQTT in the same loop(). Therefore, when reading sensors you cannot call delay() — the pause breaks the network session. Sensors are polled on a timer, and the ready value is simply read. Ready-made drivers from the ecosystem are already structured this way.

Step 1. SHT31: cabinet climate

You do not need to write the SHT31 driver from scratch — a ready-made Sht31ClimateSensor class is available in the iDryer-Storage example. It uses the robtillaart/SHT31 library and reads the sensor without blocking.

1. Add the SHT31 library to lib_deps in your platformio.ini:

   lib_deps =
       file://path/to/idryer-core
       bblanchon/ArduinoJson @ ^6.21.0
       knolleary/PubSubClient
       robtillaart/SHT31 @ ^0.5.0
   

2. Copy four files from iDryer-Storage/src/storage/sensors/ to your src/ folder: Sht31ClimateSensor.h, Sht31ClimateSensor.cpp, IClimateSensor.h, and sensor_reading.h.

3. Connect the sensor via I2C (see Wiring diagram) and read it in src/main.cpp:

#include <Wire.h>
#include <iDryer.h>
#include "Sht31ClimateSensor.h"

static Sht31ClimateSensor s_climate(&Wire);
static bool               s_climateOk = false;

void setup() {
    Serial.begin(115200);
    Wire.begin(8, 9);                 // SDA, SCL — pins on your board
    s_climateOk = s_climate.begin();  // auto-finds address 0x44 or 0x45
    s_link.begin();
}

void loop() {
    s_link.loop();

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

The SensorReading structure (fields ok, temperature, humidity) is declared in sensor_reading.h. After flashing, cabinet temperature and humidity will appear on the portal — this is the first feedback from the device.

Step 2. Thermistor: heater temperature

I do not have a ready-made thermistor class for ESP32, so we read and write directly in src/main.cpp. The thermistor is connected to an ADC pin through a voltage converter (see Wiring diagram): the controller measures the voltage at the midpoint, the thermistor resistance is calculated from it, and then the temperature.

#include <math.h>

static const int   THERM_PIN  = 2;         // ADC pin
static const float SERIES_R   = 4700.0f;   // divider resistor, Ohm
static const float NOMINAL_R  = 100000.0f; // thermistor resistance at 25 °C, Ohm
static const float NOMINAL_T  = 25.0f;     // °C
static const float BETA       = 3950.0f;   // B-coefficient from thermistor datasheet

// Returns heater temperature in °C.
static float readHeaterTempC() {
    int   raw = analogRead(THERM_PIN);          // 0..4095 on ESP32
    float v   = (float)raw / 4095.0f;           // fraction of full scale
    float r   = SERIES_R * (1.0f - v) / v;      // thermistor resistance, Ohm
    // Steinhart–Hart equation (B-parameter):
    float tK  = 1.0f / (1.0f / (NOMINAL_T + 273.15f) + logf(r / NOMINAL_R) / BETA);
    return tK - 273.15f;
}

In loop() write the result to telemetry alongside SHT31 reading:

s_link.telemetry.heaterTempC[0] = readHeaterTempC();

This is simplified reading — adjust parameters for your thermistor

The NOMINAL_R and BETA constants depend on the specific thermistor — get them from its datasheet (common household thermistor — Generic 3950, 100 kΩ). The divider formula corresponds to the circuit in Wiring diagram: thermistor to 3.3V, resistor to GND. With a different layout, the formula changes. The ADC on ESP32 is nonlinear, so for accurate measurements readings are calibrated — in production iDryer controllers a thermistor table is used for this (library Thermistor).

Checking the thermistor with a multimeter — Checking a thermistor.

Complete src/main.cpp after this chapter

Below is the entire file. New lines relative to the previous chapter are marked // ← chapter 5; the rest is unchanged.

What was — src/main.cpp after chapter 4

#include <iDryer.h>

static const iDryer::Config CFG = {
    .deviceType        = iDryer::DeviceType::Dryer,
    .unitsCount        = 1,
    .hasHeater         = true,
    .hasFan            = true,
    .hasAirTemp        = true,
    .hasAirHumidity    = true,
    .hasHeaterTemp     = true,
    .telemetryPeriodMs = 5000,
    .statusPeriodMs    = 10000,
    .hardwareVersion   = "1.0",
    .firmwareVersion   = "0.1.0",
    .model             = "DIY Storage Cabinet",
};
static iDryer::Link s_link(CFG);

void setup() {
    Serial.begin(115200);
    s_link.begin();
}

void loop() {
    s_link.loop();
}

#include <iDryer.h>
#include <Wire.h>                  // ← chapter 5
#include <math.h>                  // ← chapter 5
#include "Sht31ClimateSensor.h"    // ← chapter 5

static const iDryer::Config CFG = {
    .deviceType        = iDryer::DeviceType::Dryer,
    .unitsCount        = 1,
    .hasHeater         = true,
    .hasFan            = true,
    .hasAirTemp        = true,
    .hasAirHumidity    = true,
    .hasHeaterTemp     = true,
    .telemetryPeriodMs = 5000,
    .statusPeriodMs    = 10000,
    .hardwareVersion   = "1.0",
    .firmwareVersion   = "0.1.0",
    .model             = "DIY Storage Cabinet",
};
static iDryer::Link s_link(CFG);

// ← chapter 5: SHT31 climate sensor
static Sht31ClimateSensor s_climate(&Wire);
static bool               s_climateOk = false;

// ← chapter 5: heater thermistor
static const int   THERM_PIN  = 2;
static const float SERIES_R   = 4700.0f;
static const float NOMINAL_R  = 100000.0f;
static const float NOMINAL_T  = 25.0f;
static const float BETA       = 3950.0f;

static float readHeaterTempC() {
    int   raw = analogRead(THERM_PIN);
    float v   = (float)raw / 4095.0f;
    float r   = SERIES_R * (1.0f - v) / v;
    float tK  = 1.0f / (1.0f / (NOMINAL_T + 273.15f) + logf(r / NOMINAL_R) / BETA);
    return tK - 273.15f;
}

void setup() {
    Serial.begin(115200);
    Wire.begin(8, 9);                 // ← chapter 5  (SDA, SCL — pins on your board)
    s_climateOk = s_climate.begin();  // ← chapter 5
    s_link.begin();
}

void loop() {
    s_link.loop();

    if (s_climateOk) {                                       // ← chapter 5
        s_climate.tick(millis());
        SensorReading r = s_climate.get();
        if (r.ok) {
            s_link.telemetry.airTempC[0]       = r.temperature;
            s_link.telemetry.airHumidityPct[0] = r.humidity;
        }
    }
    s_link.telemetry.heaterTempC[0] = readHeaterTempC();     // ← chapter 5
}

Verification of result

After this step, three values should be displayed on the portal:

• air temperature in the cabinet;
• humidity in the cabinet;
• heater temperature.

If readings "float" or are clearly incorrect:

• check common ground and wiring (noise from power wires) — Wiring mistakes;
• check the divider resistor rating and thermistor type;
• make sure SHT31 responds on I2C (correct address and lines).

Diagnostics for "sensor shows garbage" — Checking a thermistor and Common mistakes.

What's next

You have data from sensors. Now we will describe device settings (target temperature, hysteresis) in YAML Menu so they can be changed from the portal and stored in memory.