arduino_pump.c

#include <Arduino.h>
#include <SoftwareSerial.h>
#define ON HIGH
#define OFF LOW

SoftwareSerial SIM900A(10, 11); // RX, TX pins
String textMessage;
String pumpState;
const int pumpPin = 12; // pump connected to pin 12

void setup() {
  pinMode(pumpPin, OUTPUT);  // configure pin 12 as OUTPUT
  digitalWrite(pumpPin, ON); // set current state of the pump to ON

  Serial.begin(9600);             // bitrate speed 9600
  SIM900A.begin(9600);            // must be the same
  SIM900A.print("AT+CMGF=1\r\n"); // set GSM to text format
  SIM900A.print(
      "AT+CNMI=2,2,0,0,0\r\n"); // NewMessageIndicator: notify micro-controller
                                // and store message on sim memory
}

void loop() {
  textMessage = "";
  if (SIM900A.available() > 0) { // new message exist?
    textMessage = SIM900A.readString();
  }
  if (textMessage == "ON") {
    // If "ON" is sent the pumps will turn on
    digitalWrite(pumpPin, ON);
    pumpState = "ON";
    SIM900A.println(
        "AT+CMGS=\"+2137979213070\""); // number with international code
    SIM900A.print("Pump is ON.\r");
    SIM900A.write(26); // 26 means execute send SMS message
  }
  if (textMessage == "OFF") {
    digitalWrite(pumpPin, OFF);
    pumpState = "OFF";
    SIM900A.println(
        "AT+CMGS=\"+2137979213070\""); /// RECEIVER: the phone number
    SIM900A.print("Pump is OFF.\r");
    SIM900A.write(0x1a); // 26 means execute send SMS message
  }
  if (textMessage == "STATUS") {
    SIM900A.print("AT+CMGF=1");
    SIM900A.println(
        "AT+CMGS=\"+2137979213070\""); /// RECEIVER: the phone number
    String message = "Pump is " + pumpState;
    SIM900A.println(message);
    SIM900A.write(0x1a); // 26 means execute send SMS message
  }
  delay(1000); // wait 1 second(1000ms)
}