1. // At commands responses will be allocated here
2. u_int8_t signal_quality;
3. char buffer[1000];
4.  
5. void configureIos () {
6.   pinMode(GSM_PWRKEY, OUTPUT);
7.   pinMode(GSM_PWREN, OUTPUT);
8.   pinMode(GPS_EN, OUTPUT);
9.   pinMode(GSM_STATUS, INPUT);
10. }
11.  
12. void configureSerial () {
13.   SerialMon.begin(38400);
14.   while (!SerialMon) {}
15.  
16.   SerialAt.begin(38400);
17.   while (!SerialAt) {}
18. }
19.  
20. /**
21.  * @brief Turn on the modem
22.  *
23.  * To be able to use the SIM868 module we have to activate the PWREN line and
24.  * make a pulse of 1.5 seconds in the PWRKEY line. The modem will have been
25.  * turned on when the STATUS line goes to high level.
26.  *
27.  * This allows the MCU to control the power of the device, necessary for low
28.  * power applications. By default the modem will be turned off and will only
29.  * turn on if we perform the turn on routine as seen in this method.
30.  *
31.  * @return true if the modem has been turned on
32.  * @return false
33.  */
34. bool powerOn () {
35.   uint8_t gsm_status;
36.  
37.   digitalWrite(GSM_PWREN, HIGH);
38.  
39.   for (char i=0; i<5; i++) {
40.     gsm_status = digitalRead(GSM_STATUS);
41.     if (gsm_status == HIGH){
42.       SerialMon.println(F("GSM HIGH!!"));
43.       break;
44.     } else {
45.       SerialMon.println(F("GSM LOW!"));
46.       digitalWrite(GSM_PWRKEY, HIGH);
47.       delay(1500);
48.       digitalWrite(GSM_PWRKEY, LOW);
49.       delay(1500);
50.     }
51.   }
52.  
53.   if (!gsm_status) {
54.     return false;
55.   }
56.  
57.   // Turn on the GPS. It is not necessary for modem operation but this demo
58.   // will make use of GPS.
59.   digitalWrite(GPS_EN, HIGH);
60.   SerialAt.println("AT+CGNSPWR=1");
61.   delay(3000);
62.  
63.   // We obviate the result of enabling GPS
64.   return true;
65. }
66.  
67. void sendAt(const char * command){
68.   memset(buffer, 0, sizeof buffer);
69.   SerialAt.println(command);
70.   uint32_t init=millis();
71.  
72.   int count=0;
73.   while ((millis() - init) < 5000) {
74.     delay(1);
75.     if (!SerialAt.available()) continue;
76.  
77.     while (SerialAt.available()) {
78.       buffer[count] = (char) SerialAt.read();
79.       count++;
80.       delay(10);
81.     }
82.  
83.     buffer[count]='\n';
84.     break; // hemos acabado, salimos del while
85.   }
86.  
87.   SerialMon.println("-");
88.   SerialMon.print("La respuesta es: ");
89.   SerialMon.println(buffer);
90. }
91.  
92. void setup () {
93.   configureIos();
94.   configureSerial();
95.  
96.   if (!powerOn()) {
97.     SerialMon.println("Fail to power on the modem. Is the SIM868 connected to the Socket 1?");
98.     for (;;) {}
99.   }
100.  
101.   sendAt("AT"); // test modem, should return "OK"
102.   if(strcmp(buffer,"OK")){
103.     sendAt("AT+SHUT");   //sets down any previous gprs conexions, should return "SHUT OK"
104.     sendAt("AT+CIPMUX=0");   //sets single conexion mode, should return "OK"
105.     sendAt("AT+CGATT=1");    //attaches GPRS Service, should return "OK"
106.     sendAt("AT+CSTT=RH_apn,RH_apnUser,RH_apnPass");
107.     sendAt("AT+CIICR"); //brings up the GPRS connexions, sometimes it takes a bit to respond, but should return "OK"
108.     sendAt("AT+CIFSR");   //gives us our IP Address
109.     sendAt("AT+CIPSTART=TCP,RH_remoteServer,RH_remotePort");
110.   }
111.  
112. }
113.  
114. bool checkCreg () {
115.   for (auto i = 0; i < 20; i++) {
116.     sendAt("AT+CREG?");
117.     if (strstr(buffer, ",1")) {
118.       // tenemos CREG!!!
119.       return true;
120.     }
121.     delay(1000);
122.   }
123.  
124.   return false;
125. }
126.  
127. void loop () {
128.   // Get GPS. It will be necessary a few minutes before obtaining data.
129.   // The important thing for this demo is not to get GPS data, but to check
130.   // that we can send a command to the modem and get a response.
131.   // SerialAt.println("AT+CGNSINF");   (Read GPS location data)
132.   // delay(1000);
133.  
134.   sendAt("AT");
135.   if (strcmp(buffer, "OK")) {
136.     SerialMon.println("El modem funciona!!");
137.   } else {
138.     SerialMon.println("Huston tenemos un problema");
139.   }
140.  
141.   if (checkCreg()) {
142.     SerialMon.println("Tenemos conexión a red!!");
143.   }
144.  
145.   //sendAt("AT+CSQ");
146.  
147.  
148.  
149.   // wait for loop
150.   delay(5000);
151. }
152.  
153. //AT+CSQ (Comando AT que indica la calidad de la señal o la cobertura)
154.