Sending Data via SIM800L GPRS to ThingSpeak

https://api.thingspeak.com/update?api_key=0F1D2F1QQUL2OHKH&field1=0

https://api.thingspeak.com/update?api_key=0F1D2F1QQUL2OHKH&field1=100

GET /update?api_key=0F1D2F1QQUL2OHKH&field1=2.8 HTTP/1.0

Sketch: Sending Atmospheric Pressure Data to ThingSpeak via SIM800L GPRS

By Roland Pelayo

Wiring:

  SIM800L TX -> D8
  SIM800L RX -> D9
  SIM800L RST -> D7
  SIM800L VCC -> 3.7V BAT+
  SIM800L GND -> 3.7V GND / Arduino GND
  BMP085 SDA -> A4
  BMP085 SCL -> A5
  BMP085 VCC -> Arduino 3.3V
  BMP085 GND - > Arduino GND
  Arduino 5V -> 3.7V BAT+

Full tutorial on: https://www.teachmemicro.com/send-data-sim800-gprs-thingspeak

*/

#include <Wire.h>
#include <Adafruit_BMP085.h>
#include <SoftwareSerial.h>
#include "Adafruit_FONA.h"

#define FONA_RX 9
#define FONA_TX 8
#define FONA_RST 7

SoftwareSerial SIM800ss = SoftwareSerial(FONA_TX, FONA_RX);
Adafruit_FONA SIM800 = Adafruit_FONA(FONA_RST);
Adafruit_BMP085 bmp;


int LED = 13;

char http_cmd[80];
char url_string[] = "api.thingspeak.com/update?api_key=0F1D2F1QQUL2OHKH&field1";
char atm_pressure_string[20];
double atm_pressure;
int net_status;

uint16_t statuscode;
int16_t length;
String response = "";
char buffer[512];

boolean gprs_on = false;
boolean tcp_on = false;

void setup() {
  pinMode(LED, OUTPUT);
  while (!Serial);

  Serial.begin(115200);
  
  Serial.println("Atmospheric Data to ThingSpeak");
  Serial.println("Initializing SIM800L....");

  SIM800ss.begin(4800); // if you're using software serial

  if (! SIM800.begin(SIM800ss)) {            
    Serial.println("Couldn't find SIM800L");
    while (1);
  }
  
  Serial.println("SIM800L is OK"); 
  delay(1000);
  
  if (!bmp.begin()) {
    Serial.println("Could not find a valid BMP085 sensor, check wiring!");
    while(1);
  }
  
  Serial.println("Waiting to be registered to network...");
  net_status = SIM800.getNetworkStatus();
  while(net_status != 1){
     net_status = SIM800.getNetworkStatus();
     delay(2000);
  }
  Serial.println("Registered to home network!");
  Serial.print("Turning on GPRS... ");
  delay(2000); 
  while(!gprs_on){
    if (!SIM800.enableGPRS(true)){  
        Serial.println("Failed to turn on GPRS");
        Serial.println("Trying again...");
        delay(2000);
        gprs_on = false;
    }else{
        Serial.println("GPRS now turned on");
        delay(2000);
        gprs_on = true;   
    } 
  }
}

void loop() {    
    digitalWrite(LED, LOW);
    atm_pressure = bmp.readPressure();
    dtostrf(atm_pressure, 5, 0, atm_pressure_string);
    sprintf(http_cmd,"%s=%s",url_string,atm_pressure_string);
    delay(2000);
    while(!tcp_on){
      if (!SIM800.HTTP_GET_start(http_cmd, &statuscode, (uint16_t *)&length)) {
           Serial.println("Failed!");
           Serial.println("Trying again...");
           tcp_on = false;
      }else{
        tcp_on = true;
        digitalWrite(LED, HIGH);
        while (length > 0) {
           while (SIM800.available()) {
             char c = SIM800.read();
             response += c;
             length--;
           }
        }
        Serial.println(response);
        if(statuscode == 200){
          Serial.println("Success!");
          tcp_on = false;
        }
        digitalWrite(LED, LOW);
      }
      delay(2000);
    }
    delay(2000);
}

The sketch follows a specific sequence to be able to send data to ThingSpeak successfully. First, the SIM800L must be turned on. This is checked here:

if (! SIM800.begin(SIM800ss)) {            
   Serial.println("Couldn't find SIM800L");
   while (1);
}
  
Serial.println("SIM800L is OK"); 
delay(1000);

if (!bmp.begin()) {
  Serial.println("Could not find a valid BMP085 sensor, check wiring!");
  while(1);
}

Similarly, the sketch will not continue down if there is no BMP085 connected.

Next, we must make sure the SIM800L is connected to the network. I created a loop that checks the network status until it is registered to the home network:

Serial.println("Waiting to be registered to network...");
net_status = SIM800.getNetworkStatus();
while(net_status != 1){
   net_status = SIM800.getNetworkStatus();
   delay(2000);
}
Serial.println("Registered to home network!");

When the SIM800L is now connected to the home network, it’s time to turn on GPRS:

Serial.print("Turning on GPRS... ");
delay(2000); 
while(!gprs_on){
  if (!SIM800.enableGPRS(true)){  
      Serial.println("Failed to turn on GPRS");
      Serial.println("Trying again...");
      delay(2000);
      gprs_on = false;
  }else{
      Serial.println("GPRS now turned on");
      delay(2000);
      gprs_on = true;   
  } 
}

atm_pressure = bmp.readPressure(); 
dtostrf(atm_pressure, 5, 0, atm_pressure_string);

sprintf(http_cmd,"%s=%s",url_string,atm_pressure_string);

SIM800.HTTP_GET_start(http_cmd, &statuscode, (uint16_t *)&length)

  while(!tcp_on){
      if (!SIM800.HTTP_GET_start(http_cmd, &statuscode, (uint16_t *)&length)) {
           Serial.println("Failed!");
           Serial.println("Trying again...");
           tcp_on = false;
      }else{
        tcp_on = true;
        digitalWrite(LED, HIGH);
        while (length > 0) {
           while (SIM800.available()) {
             char c = SIM800.read();
             response += c;
             length--;
           }
        }
        Serial.println(response);
        if(statuscode == 200){
          Serial.println("Success!");
          tcp_on = false;
        }
        digitalWrite(LED, LOW);
      }
      delay(2000);
    }