Circuit Documentation

Summary of the Circuit

This circuit is designed to interface an Arduino UNO with a SIM900A GSM module and an I2C LCD 16x2 screen. The purpose of the circuit is to send an SMS message when a toggle switch is pressed and display a confirmation message on the LCD screen. The Arduino UNO serves as the central controller, managing the communication between the SIM900A module and the LCD screen. A resistor is used in conjunction with the toggle switch to form a simple input circuit for the Arduino. The DC Source provides a stable 5V supply to the components that require it.

Component List

Arduino UNO

• Microcontroller board based on the ATmega328P
• Provides digital and analog I/O pins
• Used for controlling the SIM900A module and the I2C LCD screen

Toggle Switch

• A simple switch that connects or disconnects the circuit
• Used to trigger the sending of an SMS message

I2C LCD 16x2 Screen

• An alphanumeric liquid crystal display
• Communicates with the Arduino via the I2C protocol
• Used to display the status of the SMS message

Resistor

• A passive two-terminal electrical component
• Resistance: 200 Ohms
• Used to form a voltage divider or pull-up/pull-down for the toggle switch

DC Source 5V

• Provides a 5V power supply
• Powers the Arduino UNO, LCD screen, and other 5V components

SIM900A

• GSM/GPRS module
• Used for sending SMS messages

Sim800l

• Another GSM/GPRS module
• Not directly used in this circuit according to the provided net list

Wiring Details

Arduino UNO

• GND connected to SIM900A GND
• D4 connected to I2C LCD SCL
• D3 connected to I2C LCD SDA
• D2 connected to one end of the Resistor and Toggle Switch Vcc
• D1 (TX) connected to SIM900A DB9-3 (RXD)
• D0 (RX) connected to SIM900A DB9-2 (TXD)

Toggle Switch

• Vcc connected to one end of the Resistor and Arduino UNO D2
• Sig connected to I2C LCD GND and DC Source 5V GND

I2C LCD 16x2 Screen

• SCL connected to Arduino UNO D4
• SDA connected to Arduino UNO D3
• GND connected to Toggle Switch Sig and DC Source 5V GND
• VCC (5V) connected to the other end of the Resistor and DC Source 5V VCC

Resistor

• One end connected to Toggle Switch Vcc and Arduino UNO D2
• The other end connected to I2C LCD VCC (5V) and DC Source 5V VCC

DC Source 5V

• VCC connected to I2C LCD VCC (5V) and one end of the Resistor
• GND connected to I2C LCD GND and Toggle Switch Sig

SIM900A

• GND connected to Arduino UNO GND
• DB9-3 (RXD) connected to Arduino UNO D1 (TX)
• DB9-2 (TXD) connected to Arduino UNO D0 (RX)

Documented Code

/*
 * This Arduino sketch interfaces with a SIM900A module and an I2C LCD screen.
 * When the toggle switch is pressed, the Arduino sends a message via the SIM900A
 * and displays a message on the I2C LCD screen.
 */

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Pin definitions
const int switchPin = 2;
const int lcdSdaPin = 3;
const int lcdSclPin = 4;
const int sim900RxPin = 1;
const int sim900TxPin = 0;

// Initialize the LCD
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  // Initialize serial communication for SIM900A
  Serial.begin(9600);
  // Initialize the LCD
  lcd.begin();
  lcd.backlight();
  // Set the switch pin as input
  pinMode(switchPin, INPUT);
}

void loop() {
  // Check if the switch is pressed
  if (digitalRead(switchPin) == HIGH) {
    // Send message via SIM900A
    sendSMS();
    // Display message on LCD
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Message Sent");
    delay(2000); // Wait for 2 seconds
  }
}

void sendSMS() {
  Serial.println("AT+CMGF=1"); // Set SMS mode to text
  delay(1000);
  Serial.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
  delay(1000);
  Serial.print("Hello, this is a test message."); // Message content
  delay(1000);
  Serial.write(26); // ASCII code for CTRL+Z to send the message
  delay(1000);
}

This code is designed to run on the Arduino UNO and handles the logic for reading the toggle switch state, sending an SMS message through the SIM900A module, and displaying a confirmation message on the I2C LCD screen.