This is part 1 of a series showing how to build a data pipeline from an Industrial Shields M-Duino PLC to a Google spreadsheet using MQTT and Node-RED. In this first part, the M-Duino reads the temperature from a Dallas DS18B20 sensor and publishes values to a Mosquitto MQTT broker over Ethernet. Parts 2 and 3 cover storing the data in Google Sheets and visualising it in a Node-RED dashboard.
What you need
- M-Duino PLC (con Ethernet)
- Power supply
- Sensor de temperatura Dallas DS18B20
- PC or Linux server (for the Mosquitto broker)
- Ethernet cable connecting the M-Duino and the PC to the same network
Installing the Mosquitto MQTT broker
Install Mosquitto on the Linux machine that will act as the broker:
$ sudo apt-get install mosquitto mosquitto-clients
Start the broker and verify it is running:
$ sudo service mosquitto start $ sudo service mosquitto status
Mosquitto is a lightweight open-source MQTT broker that runs on any Linux device, including a Raspberry Pi.
Connecting the DS18B20 sensor
Connect the DS18B20 to Pin 2 of the M-Duino PLC. See the Dallas temperature sensor post for the full wiring diagram:
DS18B20 wiring with M-Duino PLC
M-Duino sketch: reading and publishing temperature
The sketch reads the DS18B20 temperature on Pin 2 every 400 ms and publishes the value as a JSON object to the MQTT topic "I". It uses the OneWire, DallasTemperature, PubSubClient, and ArduinoJson (v5) libraries.
Before uploading the sketch, set the M-Duino IP address and broker IP to match your network. After uploading, set your PC Ethernet port IP to 10.10.12.2 (or adjust the code to match your network).
#include <OneWire.h>
#include <DallasTemperature.h>
const int oneWirePin = 2;
OneWire oneWireBus(oneWirePin);
DallasTemperature sensor(&oneWireBus);
#ifdef MDUINO_PLUS
#include <Ethernet2.h>
#else
#include <Ethernet.h>
#endif
#include <ArduinoJson.h> // v5 API
#include <PubSubClient.h>
#define MQTT_ID "demo"
#define NUM_ZONES 1
#define NUM_DIGITAL_INPUTS_PER_ZONE 7
#define DIGITAL_INPUTS_OFFSET 0
const int digitalInputs[NUM_ZONES][NUM_DIGITAL_INPUTS_PER_ZONE] = {
{I0_0, I0_1, I0_2, I0_3, I0_4, I0_5}
};
byte mac[] = { 0xDE, 0xED, 0xBA, 0xFE, 0xFE, 0xAE };
IPAddress ip(10, 10, 12, 2);
IPAddress broker(10, 10, 12, 1);
unsigned port = 1883;
EthernetClient client;
PubSubClient mqtt(client);
int digitalInputsValues[NUM_ZONES][NUM_DIGITAL_INPUTS_PER_ZONE];
void setup() {
Serial.begin(9600);
sensor.begin();
Ethernet.begin(mac, ip);
mqtt.setServer(broker, port);
for (int i = 0; i < NUM_ZONES; ++i)
for (int j = 0; j < NUM_DIGITAL_INPUTS_PER_ZONE; ++j)
digitalInputsValues[i][j] = digitalRead(digitalInputs[i][j]);
}
void loop() {
if (!mqtt.connected()) {
Serial.println("Not connected to mqtt");
reconnect();
} else {
Serial.println("Connected to mqtt");
mqtt.loop();
}
updateInputs();
}
void updateInputs() {
for (int i = 0; i < NUM_ZONES; ++i)
for (int j = 0; j < NUM_DIGITAL_INPUTS_PER_ZONE; ++j)
updateDigitalInput(i, j);
}
void updateDigitalInput(int zone, int index) {
if (digitalInputs[zone][index] == oneWirePin) {
sensor.requestTemperatures();
float value = sensor.getTempCByIndex(0);
Serial.println(value);
publishInput(zone, index + DIGITAL_INPUTS_OFFSET, value);
delay(400);
}
}
void reconnect() {
if (mqtt.connect(MQTT_ID)) {
mqtt.subscribe("I");
Serial.println("Subscribed to I");
} else {
Serial.println("Closing mqtt");
client.stop();
}
}
void publishInput(int zone, int index, float value) {
DynamicJsonBuffer json(JSON_OBJECT_SIZE(3)); // ArduinoJson v5
JsonObject &root = json.createObject();
if (root.success()) {
root["zone"] = zone;
root["index"] = index;
root["value"] = value;
publish("I", root);
}
}
void publish(const char *topic, JsonObject &root) {
unsigned len = root.measureLength();
if (len > 0) {
char *payload = new char[len + 1];
if (payload) {
root.printTo(payload, len + 1);
publish(topic, payload);
delete[] payload;
}
}
}
void publish(const char *topic, const char *payload) {
if (mqtt.connected()) mqtt.publish(topic, payload);
}Note: this sketch uses the ArduinoJson v5 API. If you have version 6 or later installed, the JsonBuffer and JsonObject API has changed. Pin ArduinoJson to version 5.x in the Library Manager if needed.
Verifying the MQTT connection
With the M-Duino connected to the broker over Ethernet, open a terminal on the broker machine and subscribe to the topic "I":
$ mosquitto_sub -h 10.10.12.1 -t I
The temperature readings published by the M-Duino will appear in JSON format every 400 ms. Once this is working, you are ready for part 2 of the series, which stores the data in a Google spreadsheet using Node-RED.
Part 2: storing data in Google Sheets with Node-RED and MQTT
Publishing DS18B20 temperature data from M-Duino PLC via MQTT