Hi,
I am new to particle and have just bought got 2 photons and have played around with a few simple demos so far ranging from leds to reading a ds18b20 temperature sensor.
Now I’ve got the real basics under my belt I wanted to start playing with some MQTT examples as this is how I plan to get all my devices talking to each other. I already have an mqtt server running and have used this with arduinos, netduinos and the like before. I also use MQTTlens to see what is going on.
So the first thing I tried was the sample app included with MQTT library, updated the settings to my server and deployed. The result was the same as my next few samples using various implementations of the same MQTT library e.g.:
I’ll explain what happens shortly…
My final attempt used the code as described in the last link which I will include below for reference.
This flashed nicely on to spark it did its usual magenta flashing, followed by what I assume is restart, green flashing light, cyan and then the light goes out (because we are controlling the RGB led).
At this point I can’t seem to attach the serial monitor and nothing really seems to happen even if I send values at the topic the photon is subscribed to (yes I’ve checked I’m publishing and subscribed to the correct topics).
After say 20-40 seconds the led fades up to bright white and off, I assume another restart, then it goes through it flashing green, cyan, off.
This repeats and I have to reset the firmware to be able to flash code again.
Any help to get this up and running will be most appreciated 
Many thanks
Andy
// This #include statement was automatically added by the Spark IDE.
#include "SparkJson/SparkJson.h"
#include "MQTT/MQTT.h"
//define your mqtt credentials
#define DEVICE_ID "spark"
#define MQTT_USER "spark"
#define MQTT_PASSWORD "core1234"
#define MQTT_SERVER "www.mqttserver.co.uk"
#define MQTT_CLIENTID "andy" //The "clientId" given with the credentials
const int sensorPin = A0;
const int led = D7;
int ledState = LOW;
char message_buff[100];
unsigned long lastPublishTime = 0;
unsigned long lastBlinkTime = 0;
// Set here the time in milliseconds between publications
int publishingPeriod = 1000; // ATTENTION !!!
// DO NOT try to set values under 200 ms or the server
// will kick you out
void callback(char* topic, byte* payload, unsigned int length);
//create our instance of MQTT object
MQTT client(MQTT_SERVER, 1883, callback);
//implement our callback method thats called on receiving data from a subscribed topic
void callback(char* topic, byte* payload, unsigned int length) {
//store the received payload and convert it to string
char p[length + 1];
memcpy(p, payload, length);
p[length] = NULL;
//print the topic and the payload received
Serial.println("topic: " + String(topic));
Serial.println("payload: " + String(p));
//call our method to parse and use the payload received
handlePayload(p);
}
void handlePayload(char* payload) {
StaticJsonBuffer<200> jsonBuffer;
//convert payload to json
JsonObject& json = jsonBuffer.parseObject(payload);
if (!json.success()) {
Serial.println("json parsing failed");
return;
}
//get value of the key "command"
const char* command = json["command"];
Serial.println("parsed command: " + String(command));
if (String(command).equals("color"))
{
const char* color = json["value"];
Serial.println("parsed color: " + String(color));
String s(color);
if (s.equals("red"))
RGB.color(255, 0, 0);
else if (s.equals("blue"))
RGB.color(0, 0, 255);
else if (s.equals("green"))
RGB.color(0, 255, 0);
}
}
void mqtt_connect() {
Serial.println("Connecting to mqtt server");
if (client.connect(MQTT_CLIENTID, MQTT_USER, MQTT_PASSWORD)) {
Serial.println("Connection success, subscribing to topic");
//subscribe to a topic
client.subscribe("/v1/"DEVICE_ID"/cmd");
}
else {
Serial.println("Connection failed, check your credentials or wifi");
}
}
void setup() {
RGB.control(true);
Serial.begin(9600);
Serial.println("Hello There, I'm your photon!");
//setup our LED pin and connect to mqtt broker
pinMode(led, OUTPUT);
//set 200ms as minimum publishing period
publishingPeriod = publishingPeriod > 200 ? publishingPeriod : 200;
mqtt_connect();
}
void loop() {
if (client.isConnected()) {
client.loop();
//publish within publishing period
if (millis() - lastPublishTime > publishingPeriod) {
lastPublishTime = millis();
publish();
}
blink(publishingPeriod / 2);
}
else {
//if connection lost, reconnect
Serial.println("retrying..");
mqtt_connect();
}
}
void publish() {
//create our json payload as {"meaning":"moisture","value":sensorvalue}
StaticJsonBuffer<100> pubJsonBuffer;
JsonObject& pubJson = pubJsonBuffer.createObject();
//define a meaning for what we're sending
pubJson["meaning"] = "moisture";
//set our value key to the sensor's reading
pubJson["value"] = analogRead(sensorPin);
//copy our json object as a char array and publish it via mqtt
char message_buff[100];
pubJson.printTo(message_buff, sizeof(message_buff));
client.publish("/v1/"DEVICE_ID"/data", message_buff);
Serial.println("Publishing " + String(message_buff));
}
void blink(int interval) {
if (millis() - lastBlinkTime > interval) {
// save the last time you blinked the LED
lastBlinkTime = millis();
if (ledState == LOW)
ledState = HIGH;
else
ledState = LOW;
// set the LED with the ledState of the variable:
digitalWrite(led, ledState);
}
}
