1.  
2. // Monitor serial (debug) and modem At commands
3. #define SerialMon SerialUSB
4. #define SerialAt Serial1 // Serial1 = UART-A
5.  
6. // At commands responses will be allocated here
7. u_int8_t signal_quality;
8. char buffer[1000];
9.  
10. void configureIos () {
11.   pinMode(GSM_PWRKEY, OUTPUT);
12.   pinMode(GSM_PWREN, OUTPUT);
13.   pinMode(GPS_EN, OUTPUT);
14.   pinMode(GSM_STATUS, INPUT);
15. }
16.  
17. void configureSerial () {
18.   SerialMon.begin(38400);
19.   while (!SerialMon) {}
20.  
21.   SerialAt.begin(38400);
22.   while (!SerialAt) {}
23. }
24.  
25. /**
26.  * @brief Turn on the modem
27.  *
28.  * To be able to use the SIM868 module we have to activate the PWREN line and
29.  * make a pulse of 1.5 seconds in the PWRKEY line. The modem will have been
30.  * turned on when the STATUS line goes to high level.
31.  *
32.  * This allows the MCU to control the power of the device, necessary for low
33.  * power applications. By default the modem will be turned off and will only
34.  * turn on if we perform the turn on routine as seen in this method.
35.  *
36.  * @return true if the modem has been turned on
37.  * @return false
38.  */
39. bool powerOn () {
40.   uint8_t gsm_status;
41.  
42.   digitalWrite(GSM_PWREN, HIGH);
43.  
44.   for (char i=0; i<5; i++) {
45.     gsm_status = digitalRead(GSM_STATUS);
46.     if (gsm_status == HIGH){
47.       SerialMon.println(F("GSM HIGH!!"));
48.       break;
49.     } else {
50.       SerialMon.println(F("GSM LOW!"));
51.       digitalWrite(GSM_PWRKEY, HIGH);
52.       delay(1500);
53.       digitalWrite(GSM_PWRKEY, LOW);
54.       delay(1500);
55.     }
56.   }
57.  
58.   if (!gsm_status) {
59.     return false;
60.   }
61.  
62.   // Turn on the GPS. It is not necessary for modem operation but this demo
63.   // will make use of GPS.
64.   digitalWrite(GPS_EN, HIGH);
65.   SerialAt.println("AT+CGNSPWR=1");
66.   delay(3000);
67.  
68.   // We obviate the result of enabling GPS
69.   return true;
70. }
71.  
72. void sendAt(const char * command){
73.   memset(buffer, 0, sizeof buffer);
74.   SerialMon.println(command);
75.   SerialAt.println(command);
76.   uint32_t init=millis();
77.  
78.   int count=0;
79.   while ((millis() - init) < 5000) {
80.     delay(1);
81.     if (!SerialAt.available()) continue;
82.  
83.     while (SerialAt.available()) {
84.       buffer[count] = (char) SerialAt.read();
85.       count++;
86.       delay(10);
87.     }
88.  
89.     buffer[count]='\n';
90.     break; // hemos acabado, salimos del while
91.   }
92.  
93.   SerialMon.print("La respuesta es: ");
94.   SerialMon.println(buffer);
95. }
96.  
97. void setup () {
98.   configureIos();
99.   configureSerial();
100.  
101.   if (!powerOn()) {
102.     SerialMon.println("Fail to power on the modem. Is the SIM868 connected to the Socket 1?");
103.     for (;;) {}
104.   }
105.  
106.   sendAt("AT"); // test modem, should return "OK"
107.   if(strcmp(buffer,"OK")){
108.     sendAt("AT+SHUT");   //sets down any previous gprs conexions, should return "SHUT OK"
109.     sendAt("AT+CIPMUX=0");   //sets single conexion mode, should return "OK"
110.     sendAt("AT+CGATT=1");    //attaches GPRS Service, should return "OK"
111.     sendAt("AT+CSTT=RH_apn,RH_apnUser,RH_apnPass");
112.     sendAt("AT+CIICR"); //brings up the GPRS connexions, sometimes it takes a bit to respond, but should return "OK"
113.     sendAt("AT+CIFSR");   //gives us our IP Address
114.     sendAt("AT+CIPSTART=TCP,RH_remoteServer,RH_remotePort");
115.   }
116.  
117. }
118.  
119. bool checkCreg () {
120.   for (auto i = 0; i < 20; i++) {
121.     sendAt("AT+CSQ");
122.     sendAt("AT+CREG?");
123.     if (strstr(buffer, ",1") || strstr(buffer, ",5")) {
124.       // tenemos CREG!!!
125.       return true;
126.     }
127.     delay(1000);
128.   }
129.  
130.   return false;
131. }
132.  
133. void loop () {
134.   // Get GPS. It will be necessary a few minutes before obtaining data.
135.   // The important thing for this demo is not to get GPS data, but to check
136.   // that we can send a command to the modem and get a response.
137.   // SerialAt.println("AT+CGNSINF");   (Read GPS location data)
138.   // delay(1000);
139.  
140.   sendAt("AT");
141.   if (strcmp(buffer, "OK")) {
142.     SerialMon.println("El modem funciona!!");
143.   } else {
144.     SerialMon.println("Huston tenemos un problema");
145.   }
146.  
147.   if (checkCreg()) {
148.     SerialMon.println("Tenemos conexión a red!!");
149.   }
150.  
151.   //sendAt("AT+CSQ");
152.  
153.  
154.  
155.   // wait for loop
156.   delay(5000);
157. }
158.  
159. //AT+CSQ (Comando AT que indica la calidad de la señal o la cobertura)
160.