Hi guys, in this article we are going to see how to make a circuit with Arduino and some other components to make a school bell automatic and not make the school staff go to press the button every time.

By the end of this article, you will have created a great system that connects with just four cables to the power supply and bell button.

Supplies

• Smartphone charger (to disassemble, I used a samsung one) (2 options)
• RTC (Real Time Clock) module DS3231
• Arduino Nano
• Hilink Power Module (if you don't want to use your phone charger and to do a cleaner job)
• Relay Module (for Arduino)

Step 1: Making the Electric Circuit

To make the circuit, all we need are, besides the components marked above, a prototyping board, a good soldering iron and an excellent soldering tin.

For the connections, you will have to rely on the diagram in the photo:

• D3 (Arduino) ? Signal (relay module)
• VIN (Arduino) ? V5 (positive of the power supply)
• GND (Arduino) ? -V5 (power supply negative) ? GND (relay module) ? GND (RTC module)
• 5V (Arduino) ? Vcc (Relay module) ? Vcc (RTC module)
• A5 (Arduino) ? SCL (RTC module)
• A4 (Arduino) ? SDA (RTC module)
• ACL ? Screw terminal Line
• ACN ? Screw terminal Neutral

Step 2: Set Time on DS3231

First of all, what you have to do is load a Sketch on the arduino board to set the time in the Real Time Clock DS3231 module. This is used to make the module memorize the time and this, thanks to the 3.3V battery, will keep the time forever.

To do this, however, you must first download the DS1307 module library which is the same as the DS3231 module from the Arduino IDE "library manager" or from this link.

Once this is done, go to file, examples, DS1307, open SetTime and load the Sketch.

Once this is done, if you load the ReadTime sketch, you will see the PRECISE time of the RTC module even after disconnecting the arduino from the power supply.

Here you can find the sketch:

#include <Wire.h>
#include <TimeLib.h>
#include <DS1307RTC.h>


const char *monthName[12] = {
  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul", "Aaug", "Sep", "Oct", "Nov", "Dec"
};


tmElements_t tm;


void setup() {
  bool parse=false;
  bool config=false;


  // get the date and time the compiler was run
  if (getDate(__DATE__) && getTime(__TIME__)) {
    parse = true;
    // and configure the RTC with this info
    if (RTC.write(tm)) {
      config = true;
    }
  }


  Serial.begin(9600);
  while (!Serial) ; // wait for Arduino Serial Monitor
  delay(200);
  if (parse && config) {
    Serial.print("DS1307 configured Time=");
    Serial.print(__TIME__);
    Serial.print(", Date=");
    Serial.println(__DATE__);
  } else if (parse) {
    Serial.println("DS1307 Communication Error :-{");
    Serial.println("Please check your circuitry");
  } else {
    Serial.print("Could not parse info from the compiler, Time=\"");
    Serial.print(__TIME__);
    Serial.print("\", Date=\"");
    Serial.print(__DATE__);
    Serial.println("\"");
  }
}


void loop() {
}


bool getTime(const char *str)
{
  int Hour, Min, Sec;


  if (sscanf(str, "%d:%d:%d", &Hour, &Min, &Sec) != 3) return false;
  tm.Hour = Hour;
  tm.Minute = Min;
  tm.Second = Sec;
  return true;
}


bool getDate(const char *str)
{
  char Month[12];
  int Day, Year;
  uint8_t monthIndex;


  if (sscanf(str, "%s %d %d", Month, &Day, &Year) != 3) return false;
  for (monthIndex = 0; monthIndex < 12; monthIndex++) {
    if (strcmp(Month, monthName[monthIndex]) == 0) break;
  }
  if (monthIndex >= 12) return false;
  tm.Day = Day;
  tm.Month = monthIndex + 1;
  tm.Year = CalendarYrToTm(Year);
  return true;
}

Step 3: Programming Arduino As a Bell

After setting the date and time to our RTC module, we need to program the Arduino so that it sounds every hour at 5am and that it sounds at the entrance (7:55) and break (10:55).

To do this, upload the sketch below to your Arduino Nano:

#include <Wire.h>
#include <TimeLib.h>
#include <DS1307RTC.h>
int RelayPin = 3;
int bell_time = 4000;


void setup() {
  Serial.begin(9600);
  while (!Serial);
  delay(200);
  pinMode(RelayPin, OUTPUT);
  digitalWrite(RelayPin, HIGH);
}


void loop() {
  tmElements_t tm;


  if (RTC.read(tm)) {
    print2digits(tm.Hour);
    Serial.write(':');
    print2digits(tm.Minute);
    Serial.write(':');
    print2digits(tm.Second);
    Serial.println();
  }


  if (tm.Hour == 7 && tm.Minute == 55 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 8 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 9 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 10 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 10 && tm.Minute == 55 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 11 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 12 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  if (tm.Hour == 13 && tm.Minute == 5 && tm.Second == 0) {
    Bell();
  }


  delay(1000);
}


void Bell() {
  digitalWrite(RelayPin, LOW);
  delay(bell_time);
  digitalWrite(RelayPin, HIGH);
}


void print2digits(int number) {
  if (number >= 0 && number < 10) {
    Serial.write('0');
  }
  Serial.print(number);
}

The only two values you can change are:

int RelayPin = 3;         //set pin to connect the relay to
int bell_time = 4000;     //modify this value to make the bell last longer or shorter

to change the duration of the bell (default: 4 seconds) and the pin to which the relay controlling the bell is connected.

To change the times, change the "hour", "minute" and "second" values in each if