Control your nightlight over the Internet - Wio Terminal

In this part of the lesson, you will send telemetry with light levels from your Wio Terminal to the MQTT broker.

Install the JSON Arduino libraries

A popular way to send messages over MQTT is using JSON. There is an Arduino library for JSON that makes reading and writing JSON documents easier.

Task

Install the Arduino JSON library.

1. Open the nightlight project in VS Code.

2. Add the following as an additional line to the lib_deps list in the platformio.ini file:

   bblanchon/ArduinoJson @ 6.17.3

   This imports ArduinoJson, an Arduino JSON library.

Publish telemetry

The next step is to create a JSON document with telemetry and send it to the MQTT broker.

Task - publish telemetry

Publish telemetry to the MQTT broker.

1. Add the following code to the bottom of the config.h file to define the telemetry topic name for the MQTT broker:

   const string CLIENT_TELEMETRY_TOPIC = ID + "/telemetry";

   The CLIENT_TELEMETRY_TOPIC is the topic the device will publish light levels to.

2. Open the main.cpp file

3. Add the following #include directive to the top of the file:

   #include <ArduinoJSON.h>

4. Add the following code inside the loop function, just before the delay:

   int light = analogRead(WIO_LIGHT);
   
   DynamicJsonDocument doc(1024);
   doc["light"] = light;
   
   string telemetry;
   serializeJson(doc, telemetry);
   
   Serial.print("Sending telemetry ");
   Serial.println(telemetry.c_str());
   
   client.publish(CLIENT_TELEMETRY_TOPIC.c_str(), telemetry.c_str());

   This code reads the light level, and creates a JSON document using ArduinoJson containing this level. This is then serialized to a string and published on the telemetry MQTT topic by the MQTT client.

5. Upload the code to your Wio Terminal, and use the Serial Monitor to see the light levels being sent to the MQTT broker.

   Connecting to WiFi..
   Connected!
   Attempting MQTT connection...connected
   Sending telemetry {"light":652}
   Sending telemetry {"light":612}
   Sending telemetry {"light":583}

💁 You can find this code in the code-telemetry/wio-terminal folder.

😀 You have successfully sent telemetry from your device.