🛠 Exposer des Variables cloud avec Particle.variable

Objectives

While Particle.function triggers an action, Particle.variable exposes a live value from the firmware, read on demand by the cloud: each device becomes a small telemetry server. Reading is done via CLI (particle get) or a simple REST GET on api.particle.io/v1/devices/<id>/<name>?format=raw, which facilitates integration with Grafana, Node-RED, or a simple script. You will expose several types (int, boolean, string), read them locally and remotely, and understand the "pull" model (the cloud reads the variable; the device does not push it).

Hardware

• 1× Particle Boron connected to the cloud
• Authenticated Particle CLI (particle token create for an OAuth2 token)
• Optional: a second Particle device to subscribe and compare publish/variable

Complete code

// Boron — Variables cloud : telemetry exposee en lecture
SYSTEM_THREAD(ENABLED);

int rssi = 0;
bool radioActive = true;
String etat = "demarrage";
float temperature = 0.0f;

void setup {
    Serial.begin(9600);
    Particle.variable("rssi", rssi);              // INT
    Particle.variable("radioActive", radioActive); // BOOL
    Particle.variable("etat", etat);               // STRING
    Particle.variable("temperature", temperature); // DOUBLE
}

void loop {
    if (Cellular.ready) {
        rssi = Cellular.RSSI;
        etat = "connectee";
    } else {
        etat = "hors-ligne";
    }
    // temperature = lire_capteur;  // votre logique ici
    Serial.printf("rssi=%d etat=%s\n", rssi, etat.c_str);
    delay(5000);
}

Readings: particle get <device> rssi then via REST:

curl "https://api.particle.io/v1/devices/<device_id>/rssi?format=raw" \
  -H "Authorization: Bearer $TOKEN"

Expected verification

particle get returns the name, type, and current value of each variable, updated between two readings. The REST GET with format=raw returns the raw value, which is convenient for scripts; without this parameter, you get JSON with name, result, and coreInfo. Disconnect the antenna or turn off the board: the read fails (device offline), which confirms the pull model — the last value is not served from a buffer.

Common errors

• Modifying the variable reference (reassigning the object instead of updating the value): depending on the Device OS version, the cloud link may be lost; update the value in place.
• Expecting history: a Variable is not a database, it is an instant read point; for history, publish to an integration service.
• Incompatible types: a variable declared as INT read with a string expectation breaks clients; document the types.
• Forgetting the Authorization: Bearer header on the API: 401 error; the token is obtained via particle token create or the OAuth2 flow.
• Confusing with Particle.publish: publish = pushed event with short TTL; variable = state pulled on demand.