Telemetry: a sensor on the card

After this page the device reads temperature and humidity from an SHT31, and the card shows their cells and your own value, the dew point.

What you need

• an SHT31 module (I2C, address 0x44 or 0x45);
• wires: SDA, SCL, 3.3 V, GND;
• in platformio.ini:

lib_deps =
    robtillaart/SHT31 @ ^0.5.0

Warning

Connect the sensor with the board powered off.

Code

#include <Arduino.h>
#include <Wire.h>
#include <SHT31.h>
#include <iDryer.h>

static const iDryer::Config CFG = {
    .deviceType      = iDryer::DeviceType::Unknown,
    .unitsCount      = 1,
    .hasAirTemp      = true,    // temperature cell
    .hasAirHumidity  = true,    // humidity cell
    .hardwareVersion = "1.0",
    .firmwareVersion = "0.1.0",
    .model           = "Climate Sensor",
};
static iDryer::Link s_link(CFG);
static SHT31 s_sht(0x44, &Wire);   // address 0x44 or 0x45, set by the module jumper

// Dew point by the Magnus formula: an example of your own value.
static float dewPointC(float t, float rh) {
    const float g = logf(rh / 100.0f) + 17.62f * t / (243.12f + t);
    return 243.12f * g / (17.62f - g);
}

static void readSensor() {
    if (s_sht.read()) {
        s_link.telemetry.airTempC[0]       = s_sht.getTemperature();
        s_link.telemetry.airHumidityPct[0] = s_sht.getHumidity();
    } else {
        // No data is NAN: the field is not sent, the card shows "—".
        s_link.telemetry.airTempC[0]       = NAN;
        s_link.telemetry.airHumidityPct[0] = NAN;
    }
}

void setup() {
    Wire.begin(8, 9);                  // SDA, SCL: pins of your board
    s_sht.begin();

    s_link.begin();
    s_link.onCommand("revoke", [](JsonObjectConst) { s_link.handleRevoke(); });

    s_link.onTelemetryPublish([](JsonObject root) {
        const float t  = s_link.telemetry.airTempC[0];
        const float rh = s_link.telemetry.airHumidityPct[0];
        if (!isnan(t) && !isnan(rh)) root["units"][0]["dewPointC"] = dewPointC(t, rh);
    });
    s_link.card().sensor("dew_point", "Dew point", "°C", "units[0].dewPointC", "temperature");

    s_link.every(2000, readSensor);    // read every 2 s
}

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

How it works

• hasAirTemp and hasAirHumidity in Config give temperature and humidity cells on the card. No portal code is needed.
• The core publishes the s_link.telemetry.* fields itself: every 30 s while at least one unit is working, otherwise every 60 s. The Config.telemetryPeriodMs and telemetryPeriodIdleMs fields change the periods; zero means the contract value.
• NAN means no data: the field is not published. Do not put zero instead, or the chart shows a false drop.
• Your own value: onTelemetryPublish adds a field to telemetry before publishing, card().sensor(id, label, unit, path, deviceClass) declares it on the card. path is the path in telemetry; deviceClass is optional and sets the icon and format.
• s_link.every(ms, fn) calls a function from loop() with the given period without blocking the connection.

Check

Within a minute after flashing, the card shows temperature, humidity and dew point. Without the sensor the cells are empty and the device keeps working.

Next

LED strip.