🛠 Variables cloud et intégration HTTP

Objectives

Expose Photon data to the cloud using Particle.variable: a read-only integer (a sensor value) and a String writable from the cloud, then query and modify them from an HTTP script — the basis of an integration hook to any backend.

Hardware

• 1 Particle Photon with a sensor on A0 (tutorial photon-capteur-adc)
• API token (particle token create) and the device ID
• Python 3 with the requests library, or curl

Complete code

// photon-variables-hook.ino — variables cloud
int sensor = 0;
String status = "idle";   // les String sont inscriptibles depuis le cloud
unsigned long derniere = 0;

void setup {
  Particle.variable("sensor", sensor);  // lecture: GET .../sensor
  Particle.variable("status", status);  // ecriture: POST .../status
}

void loop {
  if (millis - derniere > 2000) {
    derniere = millis;
    sensor = analogRead(A0);            // 12 bits, 0..4095
  }
}

Expected verification

Read: curl -H "Authorization: Bearer $TOKEN" https://api.particle.io/v1/devices/<ID>/sensor returns the value. Write: curl -H "Authorization: Bearer $TOKEN" -d value=mode_nuit https://api.particle.io/v1/devices/<ID>/status modifies the String on the firmware side. In Python, requests.get followed by r.json does the same job.

Common errors

• Passing a local variable: Particle.variable must point to a global variable that lives for the entire duration of the program.
• Changing a variable's type between two firmwares without re-claiming: the cloud may reject the new schema.
• Polling too aggressively from your HTTP hook: be mindful of the API and Wi-Fi, keep an interval of several seconds.
• Forgetting that the endpoint is api.particle.io: the old api.spark.io has been permanently closed.