Playing With IoT, MQTT, Arduino, and Raspberry Pi

I’ve been playing with MQTT in previous posts and today, I want to build a simple dashboard. Basically, I’ve got a 3.5-inch display for my Raspberry Pi and I want to use it. The idea is to set up my Raspberry Pi as a web kiosk and display the MQTT variables in real time using WebSockets.

Let’s start.

Setting up a Raspberry Pi as a web kiosk is pretty straightforward. You only need to follow the instructions detailed here. Now we will prepare the MQTT inputs. Today, we’re going to reuse an example from a previous post: a potentiometer controlled by a nodeMCU microcontroller connected to our MQTT server via Wi-Fi.

We also will build another circuit using an Arduino board and an Ethernet shield.

With this circuit, we’ll register the temperature (using an LM35 temperature sensor), a photo resistor (CDS) to show the light level, and a relay to switch on/off a light bulb. The idea of the circuit is to emit the temperature and light level to the Mosquitto MQTT server and listen to the switch status from the MQTT server to fire the relay. That’s the Arduino code

#include <SPI.h> 
#include <Ethernet.h> 
#include <PubSubClient.h>

const int photocellPin = 1;
const int tempPin = 0;
const int relayPin = 9;
bool lightStatus = false;

const byte mac[] = {
    0xDE,
    0xAD,
    0xBE,
    0xEF,
    0xFE,
    0xED
};

// mqtt configuration
const char * mqttServer = "192.168.1.104";
const int mqttPort = 1883;
const String topicLightChange = "sensors/arduino/light/change";
const String topicLightStatus = "sensors/arduino/light/status";
const String topicTemp = "sensors/arduino/temperature/room1";
const String topicLight = "sensors/arduino/light/room1";
const char * clientName = "com.gonzalo123.arduino";

EthernetClient ethClient;
PubSubClient client(ethClient);

void mqttReConnect() {
    while (!client.connected()) {
        Serial.print("Attempting MQTT connection...");
        if (client.connect(clientName)) {
            Serial.println("connected");
            client.subscribe(topicLightChange.c_str());
        } else {
            Serial.print("failed, rc=");
            Serial.print(client.state());
            Serial.println(" try again in 5 seconds");
            delay(5000);
        }
    }
}

void mqttEmit(String topic, String value) {
    if (client.publish((char * ) topic.c_str(), (char * ) value.c_str())) {
        //Serial.print("Publish ok (topic: ");
        //Serial.print(topic);
        //Serial.print(", value: ");
        //Serial.print(value);
        //Serial.println(")");
    } else {
        Serial.println("Publish failed");
    }
}

void callback(char * topic, byte * payload, unsigned int length) {
    Serial.print("Message arrived [");
    Serial.print(topic);
    Serial.print("] payload: ");
    String data;
    for (int i = 0; i < length; i++) {
        data += (char) payload[i];
    }

    if (strcmp(topic, topicLightChange.c_str()) == 0) {
        lightStatus = (data == "1") ? true : false;
        Serial.print(data);
    }

    Serial.println("");
}

void setup() {
    Serial.begin(9600);
    pinMode(relayPin, OUTPUT);
    digitalWrite(relayPin, LOW);

    client.setServer(mqttServer, mqttPort);
    client.setCallback(callback);
    if (Ethernet.begin(mac) == 0) {
        Serial.println("Failed to configure Ethernet using DHCP");
    }

    delay(1500);
}

void loop() {
    if (!client.connected()) {
        mqttReConnect();
    }

    client.loop();

    if (lightStatus == 1) {
        digitalWrite(relayPin, HIGH);
    } else {
        digitalWrite(relayPin, LOW);
    }
    mqttEmit(topicLightStatus, lightStatus ? "1" : "0");
    mqttEmit(topicLight, (String) analogRead(photocellPin));
    mqttEmit(topicTemp, (String)((5.0 * analogRead(tempPin) * 100.0) / 1024.0));

    delay(500);
}

Now we’re going to work with the dashboard. These days, I’m working with OpenUI5 within various projects and because of that, we’ll use this library to build the dashboard. We’ll build something like this:

Basically, it’s a view:

<mvc:View
        controllerName="gonzalo123.controller.Controller"
        height="100%"
        width="100%"
        xmlns="sap.m"
        xmlns:mvc="sap.ui.core.mvc"
        xmlns:app="http://schemas.sap.com/sapui5/extension/sap.ui.core.CustomData/1"
>
    <IconTabBar expandable="false"
                stretchContentHeight="true"
                class="sapUiResponsiveContentPadding">
        <items>
            <IconTabFilter icon="sap-icon://bbyd-dashboard">
                <TileContainer>
                    <StandardTile
                            icon="sap-icon://explorer"
                            number="{/potentiometer}"
                            numberUnit="%"
                            title="{i18n>potentiometer}"/>
                    <StandardTile
                            icon="sap-icon://temperature"
                            number="{/temperature}"
                            numberUnit="ºC"
                            title="{i18n>temperature}"/>
                    <StandardTile
                            icon="sap-icon://lightbulb"
                            number="{/light/level}"
                            title="{i18n>light}"/>
                </TileContainer>
            </IconTabFilter>
            <IconTabFilter icon="sap-icon://lightbulb">
                <Page showHeader="false"
                      enableScrolling="true">
                    <List>
                        <InputListItem label="{i18n>light}">
                            <Switch state="{/light/status}"
                                    change="onStatusChange"/>
                        </InputListItem>
                    </List>
                </Page>
            </IconTabFilter>
        </items>
    </IconTabBar>
</mvc:View>

And a controller:

sap.ui.define([
        'jquery.sap.global',
        'sap/ui/core/mvc/Controller',
        'sap/ui/model/json/JSONModel',
        "sap/ui/model/resource/ResourceModel",
        'gonzalo123/model/io'
    ],

    function (jQuery, Controller, JSONModel, ResourceModel, io) {
        "use strict";

        io.connect("//192.168.1.104:3000/");

        return Controller.extend("gonzalo123.controller.Controller", {
            model: new JSONModel({
                light: {
                    status: false,
                    level: undefined
                },
                potentiometer: undefined,
                temperature: undefined
            }),

            onInit: function () {
                var model = this.model;
                io.on('mqtt', function (data) {
                    switch (data.topic) {
                        case 'sensors/arduino/temperature/room1':
                            model.setProperty("/temperature", data.payload);
                            break;
                        case 'sensors/arduino/light/room1':
                            model.setProperty("/light/level", data.payload);
                            break;
                        case 'sensors/nodemcu/potentiometer/room1':
                            model.setProperty("/potentiometer", data.payload);
                            break;
                        case 'sensors/arduino/light/status':
                            model.setProperty("/light/status", data.payload == "1");
                            break;
                    }
                });

                this.getView().setModel(this.model);

                var i18nModel = new ResourceModel({
                    bundleName: "gonzalo123.i18n.i18n"
                });

                this.getView().setModel(i18nModel, "i18n");
            },

            onStatusChange: function () {
                io.emit('mqtt', {
                    topic: 'sensors/arduino/light/change',
                    payload: (this.getView().getModel().oData.light.status ? "1" : "0")
                });
            }
        });
    }
);

For the real-time part, we need a gateway between WebSockets and the MQTT data. We’ll use socket.io. Here is the server:

var mqtt = require('mqtt');
var mqttClient = mqtt.connect('mqtt://192.168.1.104');
var httpServer = require('http').createServer();
io = require('socket.io')(httpServer, {origins: '*:*'});

io.on('connection', function(client){
    client.on('mqtt', function(msg){
        console.log("ws", msg);
        mqttClient.publish(msg.topic, msg.payload.toString());
    })
});

mqttClient.on('connect', function () {
    mqttClient.subscribe('sensors/#');
});

mqttClient.on('message', function (topic, message) {
    console.log("mqtt", topic, message.toString());
    io.sockets.emit('mqtt', {
        topic: topic,
        payload: message.toString()
    });
});

httpServer.listen(3000, '0.0.0.0');

Hardware

• 1 Arduino Uno
• 1 NodeMCU (V3)
• 1 potentiometer
• 1 Servo (SG90)
• 1 Raspberry Pi 3
• 3.5inch Display Hat for Raspberry Pi
• LM35
• CDS
• Pull down resistor

The source code is available in my GitHub repository.