Request Sensor Data From Your MKR GSM 1400 via SMS

Introduction

In this tutorial, we will focus on retrieving environmental data over the GSM network, using the MKR GSM 1400 and MKR ENV shield. We will set it up so that when a phone sends an SMS to the board, it will read the sensors on the shield, and reply to the sender with a list of the sensor data inside an SMS.

Goals

The goals of this project are:

• Set up a simple data request over GSM.
• Read the sensors on the MKR ENV shield.
• Listen for incoming texts, and if we get a request, reply with the sensor data to the sender's number.

Hardware & Software Needed

• Arduino IDE (online or offline).
• MKRGSM library installed.
• Arduino MKR GSM 1400.
• MKR ENV shield.
• Antenna.
• SIM card from an operator in your country.

Requesting Data over GSM

Practically speaking, the setup we will create is very basic:

• An SMS containing a specific keyword, which we name

  data

  , is sent to the board.
• The board checks if the content of the SMS is equal to

  data

  .
• If it is a match, the board reads the sensors on the MKR ENV shield, and replies with a text message to the sender.
• The text message contains sensor data a description of what type of data it is.

The SMS request method is quite practical, easy to setup and as it operates within the GSM, there is almost always coverage, even in more rural parts.

Circuit

Programming the Board

We will now get to the programming part of this tutorial.

1. First, let's make sure we have the drivers installed. If we are using the Web Editor, we do not need to install anything. If we are using an offline editor, we need to install it manually. This can be done by navigating to Tools > Board > Board Manager.... Here we need to look for the Arduino SAMD boards (32-bits Arm® Cortex®-M0+) and install it.

2. Now, we need to install the libraries needed. If we are using the Web Editor, there is no need to install anything. If we are using an offline editor, simply go to Tools > Manage libraries.., and search for MKRGSM and Arduino_MKRENV and install them.

3. We can now take a look at some of the core functions of this sketch:

• GSM gsmAccess

  - base class for all GSM functions.

• GSM_SMS sms

  - base class for all GSM functions for SMS.

• gsmAccess.begin(pin)

  - connects to the GSM network with the pin number as a parameter, e.g. 0123.

• sms.available()

• sms.remoteNumber(number, 20)

  - retrieves a sender's number.

• equals()

  - function that checks if a

  string

  is exactly the same as

  string2

  .

• sms.beginSMS(number);

  - creates an SMS for a specific number.

• sms.print(message);

  - prints the content of the SMS.

• sms.endSMS()

  - sends the SMS.

• sms.flush()

  - deletes the message from the modem memory.

• ENV.begin()

  - initializes the Arduino_MKRENV library.

• ENV.readSensor()

  - retrieves sensor data from the MKR ENV shield. Replace readSensor with for example readTemperature.

The sketch can be found in the snippet below. Upload the sketch to the board.

Copy
1#include <MKRGSM.h>
2#include <Arduino_MKRENV.h>
3
4#include "arduino_secrets.h"
5// Please enter your sensitive data in the Secret tab or arduino_secrets.h
6// PIN Number
7const char PINNUMBER[] = "YOUR_PIN";
8
9// initialize the library instances
10GSM gsmAccess;
11GSM_SMS sms;
12
13String message;
14String data_request = "data"; //used for comparison
15
16//variables for sensor data
17double temperature;
18double humidity;
19double pressure;
20double uva;
21double uvb;
22
23// Array to hold the number a SMS is retrieved from
24char senderNumber[20];
25
26void setup() {
27  // initialize serial communications and wait for port to open:
28  Serial.begin(9600);
29  pinMode(LED_BUILTIN, OUTPUT);
30
31  while (!Serial) {
32    ; // wait for serial port to connect. Needed for native USB port only
33  }
34
35  if (!ENV.begin()) {
36    Serial.println("Failed to initialize MKR ENV shield!");
37    while (1);
38  }
39
40  Serial.println("SMS environmental data request");
41
42  // connection state
43  bool connected = false;
44
45  // Start GSM connection
46  while (!connected) {
47    if (gsmAccess.begin(PINNUMBER) == GSM_READY) {
48      connected = true;
49    } else {
50      Serial.println("Not connected");
51      delay(1000);
52    }
53  }
54
55  Serial.println("GSM initialized");
56  Serial.println("Waiting for messages");
57  Serial.println();
58}
59
60void loop() {
61  int c;
62
63  // If there are any SMS available()
64  if (sms.available()) {
65
66  //only read sensors if a request comes in
67    temperature = ENV.readTemperature();
68    humidity    = ENV.readHumidity();
69    pressure    = ENV.readPressure();
70    uva         = ENV.readUVA();
71    uvb         = ENV.readUVB();
72
73    Serial.println("Request from:");
74
75    // Get remote number
76    sms.remoteNumber(senderNumber, 20);
77    Serial.println(senderNumber);
78
79    Serial.print("Message: ");
80    // Read message bytes and print them
81    while ((c = sms.read()) != -1) {
82      Serial.print((char)c);
83
84      //print incoming message to the "message" string
85      message += (char)c;
86    }
87
88    //print empty line to separate incoming message from LED status message
89    Serial.println();
90
91    //if incoming message is exactly "ON", turn on LED
92    if (message.equals(data_request)) {
93
94      Serial.println("Data has been requested.");
95      Serial.println();
96
97
98      //begin constructing an SMS containing sensor data
99      sms.beginSMS(senderNumber);
100      sms.print("temp: ");
101      sms.print(temperature);
102      sms.print(", humidity: ");
103      sms.print(humidity);
104      sms.print(", pressure: ");
105      sms.print(pressure);
106      sms.print(", uva: ");
107      sms.print(uva);
108      sms.print(", uvb: ");
109      sms.print(uvb);
110
111      //send the SMS
112      sms.endSMS();
113
114      //print the data in the Serial Monitor
115      Serial.print("temp: ");
116      Serial.println(temperature);
117      Serial.print("humidity: ");
118      Serial.println(humidity);
119      Serial.print("pressure: ");
120      Serial.println(pressure);
121      Serial.print("uva: ");
122      Serial.println(uva);
123      Serial.print("uvb: ");
124      Serial.println(uvb);
125      Serial.println();
126
127      Serial.print("Above environmental data sent to: ");
128      Serial.println(senderNumber);
129    }
130
131    Serial.println("\nEND OF MESSAGE");
132
133    // Delete message from modem memory
134    sms.flush();
135
136    // Clear message string
137    message = "";
138    Serial.println("MESSAGE DELETED");
139    Serial.println();
140  }
141
142  delay(1000);
143
144}

Testing It Out

After we have successfully uploaded the code to the board, open the Serial Monitor. We should now see the text

"SMS environmental data request"

"Waiting for messages"

Now we need to create a new SMS that only contains the phrase

data

equal()

If the incoming message is exactly

data

We should now get a reply on the phone that we sent the request from, which lists the sensor data!

Troubleshoot

If the code is not working, there are some common issues we can troubleshoot:

• We have not installed the MKRGSM library.
• We have entered the wrong pin number.
• We are out of coverage (no signal).
• We have tried to send a request to the wrong number.
• SIM card may not be activated.
• The request is not properly made. Remember that we need to send

  data

  . If we send

  Data

  or

  DATA

  , it will not work.

Conclusion

In this tutorial, we have created a very basic setup for requesting environmental data, using the MKR GSM 1400 board and the MKR ENV shield. The request, using the GSM_SMS class, simply allows anyone on a phone to send the phrase

data

Feel free to explore the MKRGSM library further, and try out some of the many cool functions in this library.