MQTT with the W5100 Ethernetshield

In a previous post I discussed the use of an old ENC28J60 ethernetshield for an MQTT node. The biggest setback of the ENC28J60 shield is that it uses a lot of memory. When using the newer W5100 Ethernetshield, there is a bit more room to play with. So here is a simple framework  for an MQTT node that doesnt’t only publish, but also reacts to simple commands that come in with a subscription.

MQTT-Spy output
MQTT-Spy output
          Arduino UNO with W5100 Ethernetshield or  W5100 Ethernet module, used as MQTT client
          It will connect over Wifi to the MQTT broker and controls a digital output (LED, relay)
          and gives the Temperature and Humidity, as well as the state of some switches
          The topics have the format "home/br/sb" for southbound messages and  "home/nb" for northbound messages
          Southbound are messages going to the client, northbound are messages coming from the client
          As the available memory of a UNO  with Ethernetcard is limited, I have kept the topics short
          Also, the payloads  are kept short
          The Northbound topics are
          home/br/nb/temp  for temperature
          home/br/nb/humid  for humidity
          home/br/nb/deur  for a door switch
          home/br/nb/l for  the lightintensity
          home/br/nb/pr  for the status of a PIR sensor
          home/br/nb/ip showing the IP number of the client
          home/br/nb/relay showing the relaystate

          There is only one southbound topic:
          The payload here determines the action:
          0 -Switch the relay off
          1-Switch the  relay on
          2-Publish the IP number of the client
          3 Ask for the relaystate REMOVED

          On Startup, the Client publishes the IP number

#include "PubSubClient.h"
#include "DHT.h"
//kennelijk  geeft update van DHT sensor library boven 1.2.1 een fout
#define CLIENT_ID       "Hal"
//#define TOPIC           "temp"
#define PUBLISH_DELAY   3000
#define PUB_TOPIC "my_username/f/temperature" //Adafruit dashboard
#define PUB_TOPIC_h "my_username/f/humidity" //Adafruit dashboard
#define DHTPIN          3
#define DHTTYPE         DHT11
#define ledPin 13
#define relayPin 8
String ip = "";
bool statusKD = HIGH;
bool statusBD = HIGH;
bool statusGD = HIGH;
bool relaystate = LOW;
bool pir = LOW;
bool startsend = HIGH;
int lichtstatus;
uint8_t mac[6] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x06};

EthernetClient ethClient;
PubSubClient mqttClient;

long previousMillis;

void setup() {
  pinMode(4, INPUT_PULLUP);
  pinMode(5, INPUT_PULLUP);
  pinMode(6, INPUT_PULLUP);
  pinMode(7, INPUT);
  pinMode(relayPin, OUTPUT);

  // setup serial communication

  while (!Serial) {};
  Serial.println(F("MQTT Arduino Demo"));

  // setup ethernet communication using DHCP
  if (Ethernet.begin(mac) == 0) {
    //Serial.println(F("Unable to configure Ethernet using DHCP"));
    for (;;);

  Serial.println(F("Ethernet configured via DHCP"));
  Serial.print("IP address: ");
  ip = String (Ethernet.localIP()[0]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[1]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[2]);
  ip = ip + ".";
  ip = ip + String (Ethernet.localIP()[3]);

  // setup mqtt client
  //mqttClient.setServer(mqttServer, 1883);
  // mqttClient.setServer("", 1883);
  //  mqttClient.setServer( "raspberrypi.local",1883);
  mqttClient.setServer( "", 1883);
  //Serial.println(F("MQTT client configured"));
  // setup DHT sensor
  Serial.println(F("DHT sensor initialized"));

  Serial.println(F("Ready to send data"));
  previousMillis = millis();
  mqttClient.publish("home/br/nb/ip", ip.c_str());

void loop() {

  statusBD = digitalRead(4);// FrontdoorSwitch
  statusGD = digitalRead(5);// Garagedoor Switch
  statusKD = (digitalRead(6));//LivingRoom Switch

  lichtstatus = analogRead(A0);//Reads an LDR
  pir = digitalRead(7);//Reads a PIR sensor
  relaystate = digitalRead(relayPin);// Reads the state of a relay

  // it's time to send new data?
  if (millis() - previousMillis > PUBLISH_DELAY) {
    previousMillis = millis();



void sendData() {

  char msgBuffer[20];
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  Serial.print("Temperature: ");
  Serial.print("Humidity: ");
  Serial.print("Relay is: ");
  Serial.println((relaystate == LOW) ? "OPEN" : "CLOSED");
  if (mqttClient.connect(CLIENT_ID)) {
    mqttClient.publish("home/br/nb/temp", dtostrf(t, 6, 2, msgBuffer));
    mqttClient.publish("home/br/nb/humid", dtostrf(h, 6, 2, msgBuffer));
    mqttClient.publish("home/br/nb/deur", (statusBD == HIGH) ? "OPEN" : "CLOSED");
    mqttClient.publish("home/br/nb/garage", (statusGD == HIGH) ? "OPEN" : "DICHT");
    mqttClient.publish("home/br/nb/bel", (statusKD == HIGH) ? "OPEN" : "CLOSED");
    mqttClient.publish("home/br/nb/l", dtostrf(lichtstatus, 4, 0, msgBuffer));
    mqttClient.publish("home/br/nb/p", (pir == HIGH) ? "OPEN" : "CLOSED");
    mqttClient.publish("home/br/nb/relay", (relaystate == LOW) ? "OPEN" : "CLOSED");
    if (startsend) {
     // mqttClient.publish("home/br/nb/relay", (relaystate == LOW) ? "OPEN" : "CLOSED");
      mqttClient.publish("home/br/nb/ip", ip.c_str());
      startsend = LOW;

void callback(char* topic, byte* payload, unsigned int length) {
  char msgBuffer[20];
  // I am only using one ascii character as command, so do not need to take an entire word as payload
  // However, if you want to send full word commands, uncomment the next line and use for string comparison
   //payload[length] = '\0';            // terminate string with '0'
  //String strPayload = String((char*)payload);  // convert to string
  // Serial.println(strPayload); //can use this if using longer southbound topics
  Serial.print("Message arrived [");
  Serial.print("] ");//MQTT_BROKER
  for (int i = 0; i < length; i++) {

  // Examine only the first character of the message
  if (payload[0] == 49)             // Message "1" in ASCII (turn output ON)
    digitalWrite(LED_BUILTIN, HIGH);    //
    digitalWrite(relayPin, HIGH);
  } else if (payload[0] == 48)      // Message "0" in ASCII (turn output OFF)
    digitalWrite(relayPin, LOW);     //
    digitalWrite(LED_BUILTIN, LOW);
  } else if (payload[0] == 50)
    mqttClient.publish("home/br/nb/ip", ip.c_str());// publish IP nr
  } else {
    Serial.println("Unknown value");
    mqttClient.publish("home/br/nb", "Syntax Error");


You will find the full code for download here.

Setting up a local MQTT broker on the Raspberry Pi

On the web there are a ton of instructions and how to’s on how to do this, but I found  it easiest to just  issue two commands on Raspian Jessie:
sudo apt-get update
sudo apt-get install mosquitto mosquitto-clients python-mosquitto

then to test if it was all working, I opened 2 ssh terminals to my raspberry with:
ssh pi@  (the latter being the ip nr from my raspberry)
and then in one of those terminals I entered:
mosquitto_sub -d -t hello/world
this made the terminal I will call Terminal 1 subscribe to the topic “hello/world”
in the other ssh terminal window (Terminal 2) I entered
mosquitto_pub -d -t hello/world -m "Greetings from Terminal2"
and immediately I got that message published in Terminal 1
(actually you don’t need the ‘-d’ option. That is just for diagnostics)
So I knew my local Mosquitto broker was working, at least within one machine, the raspberry on which it was installed. Time to check if it also worked on other machines. To do that I opened a third terminal on my desktop that didnt ssh to the raspberry but just gave a command line to the machine I was working on (a regular Linux desktop).

Before I could have that machine subscribe to an MQTT topic, I first had to install the MQTT client with:
sudo apt-get install mosquitto-clients

when that was done I entered:
mosquitto_sub -h -t hello/world

mosquitto-terminalNow when I published a message on terminal2 (thats the raspberry) it got published on terminal1 (that same raspberry) and on terminal3 (a regular desktop), so now I knew everything was hunky dory.
However, having to use terminal command lines to check your MQTT broker is not the most convenient. I can advise everybody who works with MQTT to install MQTT-spy. That is a jar file that basically is a publisher and a client that keeps track of MQTT messages on your network.

It comes pre-configured with 3 public brokers but adding your local broker is very simple:
mqtt-localAfter starting MQTT-spy go to  ‘Connections-New Connection” Fill out a name for your connection and under the ‘connectivity tab’ add (in my case):  with 1883 being the  standard MQTT port.
Then go to the ‘other’tab and check ‘auto subscribe when opened’.
Now in the main window add a subscription tab called ‘hello/world’ and republish  the messagemqttspy-3 from Terminal2: it should appear in the receive window of mqtt-spy. Vice versa, if  you publish a message from within mqtt spy, it will appear on terminal 1 also