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Goal: flip a Switch on the dashboard and toggle a pin on the device.

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1. Add a Switch

In the designer, drop a Switch and configure the command it sends in the Triggers tab. A command arrives at the device as structured JSON, for example: 
{
  "from": "controller-xyz",
  "payload": {
    "commands": [
      {
        "command": "GPIO_MANAGEMENT",
        "actions": [
          { "action": "ON", "params": { "gpio": 12, "pinmode": "OUTPUT", "status": "HIGH" } }
        ]
      }
    ]
  }
}

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2. Handle the command in firmware

Register a handler and use the JSON helpers to pull out the command, action, and params: 
void setup() {
  Serial.begin(115200);

  device.setUserCommandHandler([](JsonObject &msg) {
    JsonObject params = device.findParams(msg, "GPIO_MANAGEMENT", "ON");
    if (!params.isNull()) {
      int pin = params["gpio"];
      pinMode(pin, OUTPUT);
      digitalWrite(pin, params["status"] == "HIGH" ? HIGH : LOW);
    }
  });

  device.begin();
}

void loop() {
  device.loop();
}
findCommand, findAction, and findParams navigate the incoming payload so you don’t parse it by hand. See the API reference.

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3. Test it

Flip the Switch in Preview. The device receives the command and toggles the pin.

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How it works

This is the down half of the core loop: a control widget → setUserCommandHandler on the device. Combined with Lesson 2, you now have a full two-way device.

Next: store readings

Persist data to the product database.