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Request Sensor Data From Your MKR GSM 1400 via SMS

Learn how to record data from the MKR ENV Shield, and setup an application that allows phones to retrieve data from it via SMS.


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.


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

Requesting Data over GSM

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

  • An SMS containing a specific keyword, which we name
    , is sent to the board.
  • The board checks if the content of the SMS is equal to
  • 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.
Requesting data from the board.
Requesting data from the board.

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.


Simple circuit with board and antenna.
Simple circuit with board and antenna.

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
    is exactly the same as
  • 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.

1#include <MKRGSM.h>
2#include <Arduino_MKRENV.h>
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";
9// initialize the library instances
10GSM gsmAccess;
11GSM_SMS sms;
13String message;
14String data_request = "data"; //used for comparison
16//variables for sensor data
17double temperature;
18double humidity;
19double pressure;
20double uva;
21double uvb;
23// Array to hold the number a SMS is retrieved from
24char senderNumber[20];
26void setup() {
27 // initialize serial communications and wait for port to open:
28 Serial.begin(9600);
31 while (!Serial) {
32 ; // wait for serial port to connect. Needed for native USB port only
33 }
35 if (!ENV.begin()) {
36 Serial.println("Failed to initialize MKR ENV shield!");
37 while (1);
38 }
40 Serial.println("SMS environmental data request");
42 // connection state
43 bool connected = false;
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 }
55 Serial.println("GSM initialized");
56 Serial.println("Waiting for messages");
57 Serial.println();
60void loop() {
61 int c;
63 // If there are any SMS available()
64 if (sms.available()) {
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();
73 Serial.println("Request from:");
75 // Get remote number
76 sms.remoteNumber(senderNumber, 20);
77 Serial.println(senderNumber);
79 Serial.print("Message: ");
80 // Read message bytes and print them
81 while ((c = != -1) {
82 Serial.print((char)c);
84 //print incoming message to the "message" string
85 message += (char)c;
86 }
88 //print empty line to separate incoming message from LED status message
89 Serial.println();
91 //if incoming message is exactly "ON", turn on LED
92 if (message.equals(data_request)) {
94 Serial.println("Data has been requested.");
95 Serial.println();
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);
111 //send the SMS
112 sms.endSMS();
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();
127 Serial.print("Above environmental data sent to: ");
128 Serial.println(senderNumber);
129 }
131 Serial.println("\nEND OF MESSAGE");
133 // Delete message from modem memory
134 sms.flush();
136 // Clear message string
137 message = "";
138 Serial.println("MESSAGE DELETED");
139 Serial.println();
140 }
142 delay(1000);

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"
followed by
"Waiting for messages"
. This means it is working, and we can now send a data request to the MKR GSM 1400 board, from our phone.

Waiting for messages.
Waiting for messages.

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

. This needs to be case sensitive, and can't include any spaces etc, because we are using the
function. This function compares one string to the other, and if it is an exact match, it will trigger the rest of the code.

If the incoming message is exactly

, the program will first read the sensors and then construct a reply, containing all sensor data. It is then sent to the number which requested it (the sender).

Request received, environmental data sent back to requester.
Request received, environmental data sent back to requester.

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


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
    . If we send
    , it will not work.


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

to a board, and receives a list of environmental data freshly recorded. This setup can be very useful for projects that are used in rural parts, where e.g. Wi-Fi is not available.

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

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