Monday, September 4, 2017

Real time clock with 2 alarms using PIC18F4550 and DS3231


Real time clock with 2 alarms and temperature sensing using PIC18F4550 and DS3231
Real time clock with 2 alarms using PIC18F4550 and DS3231 hardware circuit 
After the simple interfacing of the PIC18F4550 microcontroller with the DS3231 RTC, now let's add the alarms functionality and temperature monitor to our previous project.
Interfacing PIC18F4550 with DS3231 project link:
Real time clock & calendar with PIC18F4550 and DS3231
As written in the datasheet the DS3231 RTC has a built-in 2 alarm functions and a digital temperature sensor with an accuracy of ±3°C.
Hardware Required:
  • PIC18F4550 microcontroller
  • 20x4 LCD screen
  • 10K ohm variable resistor
  • 330 ohm resistor
  • LED
  • 3 x push button
  • 5V supply source
  • Breadboard
  • Jumper wires
DS3231 board contains the following components:
  • DS3231 RTC - datasheet
  • 3 x 4.7K ohm resistors
  • 0.1uF ceramic capacitor
  • 3V coin cell battery
The circuit:
Project circuit diagram is shown below.
PIC18F4550 MCU and DS3231 real time clock with two alarms and temperature monitor circuit
To simplify the circuit, I used the DS3231 board, this board basically contains the main chip which is the DS3231, pull-up resistors (4.7K) of SCL, SDA and INT/SQW lines and coin cell battery holder. There is also 24C32 EEPROM and some other resistors (not used in this project).
The DS3231 board is supplied with 5V as the microcontroller and the 2004 LCD, there are 3 data lined connected between this board and the PIC18F4550 MCU, SCL line is connected to pin RB1, SDA is connected to pin RB0 and INT line is connected to pin RB2 which is the external interrupt 2 pin of the PIC18F4550 MCU. The DS3231 interrupts the microcontroller when there is an alarm.
In the circuit there are 3 push buttons: B1, B2 and B3. These buttons are used to set time, calendar and alarms. Time and calendar can be adjusted with B1 and B2, button B1 selects time or date parameter (time parameters: hours and minutes; calendar parameters: day, date, month and year) and B2 increments the selected parameter. The button B3 and B2 adjust alarm1 and alarm2 parameters (hours, minutes and ON/OFF), button B3 selects the parameter and B2 increments the selected parameter.
There is an LED connected to pin RB6, this LED is used as an alarm indicator (alarm1 or alarm2), so if there is an alarm the DS3231 pulls down the INT pin which interrupts the microcontroller and the microcontroller turns the LED ON, here button B2 turns both the LED and the occurred alarm OFF.
In this project the PIC18F4550 MCU uses its internal oscillator and MCLR pin function is disabled.
CCS C code:
The C code below was tested with CCS C compiler version 5.051.
By reading the datasheet of the DS3231 RTC the code will be more easier!
The hardware I2C module of the MCU is initialized and configured using the following CCS C function with a speed of 100KHz:
#use I2C(master, I2C1, FAST = 100000)
master: set the microcontroller to the master mode
I2C1: use first I2C module.
The DS3231 works with BCD format only (except temperature) and to convert the BCD to decimal and vise versa I used the following functions (example for minute variable):
minute = (minute >> 4) * 10 + (minute & 0x0F);                                  // Convert BCD to decimal
minute = ((minute / 10) << 4) + (minute % 10);                                   // Convert decimal to BCD

Code functions:
void DS3231_read() : this function reads time and calendar data from the DS3231 (seconds, minutes, hours, day, date, month and year).
void DS3231_display() : displays time and calendar data, before displaying time and calendar data are converted from BCD format to decimal format. This function displays the calendar by calling a function named void calendar_display() .
void alarms_read_display() : basically this functions reads alarm1 and alarm2 minutes and hours. It also reads the DS3231 control register, status register and 2 temperature registers.
The other job of this function is to display alarms data (hours, minutes and status) and the temperature value. The alarm status are extracted from the control register.
int8 edit(parameter, x, y) : I used this function to edit time, calendar and alarm parameters except the day. I used a variable named i to distinguish between the parameters:
i = 0, 1 : time hours and minutes respectively
i = 2, 3, 4: date month, year respectively
i = 5, 6: alarms hours and minutes respectively
i = 7: alarms status (ON or OFF)
After the edit of time/calendar/alarms the data have to be converted back to BCD format and written to the DS3231.
The MCU turns the LED ON when it interrupted by the DS3231, the DS3231 sends the interrupt signal (pulls down the INT line) when there has been an alarm. Button B2 resets and turns OFF the alarm. If both alarms are active, button B2 will resets and turns OFF the occurred alarm only and keeps the other as it is. To do that we've to detect which alarm was occurred which can be easily done by reading the status register of the DS3231 (A1IF and A2IF flag bits). Turning ON or OFF an alarm is done by writing to the control register (bits: INTCN, A1IE and A2IE). Always INTCN bit should be 1. I used the following line to write 1 to the INTCN bit and to turn OFF the occurred alarm:
i2c_write(4 | (!bit_test(status_reg, 0) & alarm1_status) | ((!bit_test(status_reg, 1) & alarm2_status) << 1));
alarm1_status and alarm2_status are 1-bit variables, for example if alarm1_status is 1 ==> alarm1 is ON and  if alarm1_status is 0 ==> alarm1 is OFF. The same thing for alarm2.
The complete C code is below.
/* Real time clock and calendar with 2 alarms and temperature sensing using
   PIC18F4550 MCU & DS3231 CCS C code.
   Read DS3231 RTC datasheet to understand the code!
   Time & date parameters can be set using two push buttons connected to pins RB3 & RB4.
   Alarm1 and alarm2 can be set using buttons connected to pins RB5 and RB4.
   Pin RB6 becmoes high when an alarm occured and button RB4 returns it to low and
   turns the occurred alarm OFF.
   DS3231 interrupt pin is connected to PIC18F4550 external interrupt 2 pin (RB2).
   http://ccspicc.blogspot.com/
   electronnote@gmail.com
*/

// LCD module connections
#define LCD_RS_PIN      PIN_D0
#define LCD_RW_PIN      PIN_D1
#define LCD_ENABLE_PIN  PIN_D2
#define LCD_DATA4       PIN_D3
#define LCD_DATA5       PIN_D4
#define LCD_DATA6       PIN_D5
#define LCD_DATA7       PIN_D6
// End LCD module connections

#include <18F4550.h>
#fuses NOMCLR, INTRC_IO, NOWDT,NOPROTECT,NOLVP
#use delay(clock = 8000000)
#include <lcd.c>
#use fast_io(B)
#use fast_io(D)
#use I2C(master, I2C1, FAST = 100000)

int1 alarm1_status, alarm2_status;
char time[]     = "  :  :  ",
     calendar[] = "      /  /20  ",
     alarm1[]   = "A1:   :  :00", alarm2[]   = "A2:   :  :00",
     temperature[] = "T:   .   C";
int8  i, second, minute, hour, day, date, month, year,
      alarm1_minute, alarm1_hour, alarm2_minute, alarm2_hour,
      status_reg;
#INT_EXT2                                        // External interrupt routine
void ext2_isr(void){
  output_high(PIN_B6);
  clear_interrupt(INT_EXT2);
}
void DS3231_read(){                              // Read time & calendar data function
  i2c_start();                                   // Start I2C protocol
  i2c_write(0xD0);                               // DS3231 address
  i2c_write(0);                                  // Send register address (seconds register)
  i2c_start();                                   // Restart I2C
  i2c_write(0xD1);                               // Initialize data read
  second = i2c_read(1);                          // Read seconds from register 0
  minute = i2c_read(1);                          // Read minuts from register 1
  hour   = i2c_read(1);                          // Read hour from register 2
  day    = i2c_read(1);                          // Read day from register 3
  date   = i2c_read(1);                          // Read date from register 4
  month  = i2c_read(1);                          // Read month from register 5
  year   = i2c_read(0);                          // Read year from register 6
  i2c_stop();                                    // Stop I2C protocol
}
void alarms_read_display(){                      // Read and display alarm1 and alarm2 data function
  int8 control_reg, temperature_lsb;
  signed int8 temperature_msb;
  i2c_start();                                   // Start I2C protocol
  i2c_write(0xD0);                               // DS3231 address
  i2c_write(0x08);                               // Send register address (alarm1 minutes register)
  i2c_start();                                   // Restart I2C
  i2c_write(0xD1);                               // Initialize data read
  alarm1_minute = i2c_read(1);                   // Read alarm1 minutes
  alarm1_hour   = i2c_read(1);                   // Read alarm1 hours
  i2c_read(1);                                   // Skip alarm1 day/date register
  alarm2_minute = i2c_read(1);                   // Read alarm2 minutes
  alarm2_hour   = i2c_read(1);                   // Read alarm2 hours
  i2c_read(1);                                   // Skip alarm2 day/date register
  control_reg = i2c_read(1);                     // Read the DS3231 control register
  status_reg  = i2c_read(1);                     // Read the DS3231 status register
  i2c_read(1);                                   // Skip aging offset resgister
  temperature_msb = i2c_read(1);                 // Read temperature MSB
  temperature_lsb = i2c_read(0);                 // Read temperature LSB
  i2c_stop();                                    // Stop I2C protocol
    // Convert BCD to decimal
  alarm1_minute = (alarm1_minute >> 4) * 10 + (alarm1_minute & 0x0F);
  alarm1_hour   = (alarm1_hour   >> 4) * 10 + (alarm1_hour & 0x0F);
  alarm2_minute = (alarm2_minute >> 4) * 10 + (alarm2_minute & 0x0F);
  alarm2_hour   = (alarm2_hour   >> 4) * 10 + (alarm2_hour & 0x0F);
    // End conversion
  alarm1[8]     = alarm1_minute % 10  + 48;
  alarm1[7]     = alarm1_minute / 10  + 48;
  alarm1[5]     = alarm1_hour   % 10  + 48;
  alarm1[4]     = alarm1_hour   / 10  + 48;
  alarm2[8]     = alarm2_minute % 10  + 48;
  alarm2[7]     = alarm2_minute / 10  + 48;
  alarm2[5]     = alarm2_hour   % 10  + 48;
  alarm2[4]     = alarm2_hour   / 10  + 48;
  alarm1_status = bit_test(control_reg, 0);      // Read alarm1 interrupt enable bit (A1IE) from DS3231 control register
  alarm2_status = bit_test(control_reg, 1);      // Read alarm2 interrupt enable bit (A2IE) from DS3231 control register
  if(temperature_msb < 0){
    temperature_msb = abs(temperature_msb);
    temperature[2] = '-';
  }
  else
    temperature[2] = ' ';
  if(temperature_msb > 99)
    temperature[2] = '1';
  temperature_lsb >>= 6;
  temperature[4] =  temperature_msb % 10  + 48;
  temperature[3] = (temperature_msb / 10) % 10  + 48;
  if(temperature_lsb == 0 || temperature_lsb == 2){
    temperature[7] = '0';
    if(temperature_lsb == 0) temperature[6] = '0';
    else                     temperature[6] = '5';
  }
  if(temperature_lsb == 1 || temperature_lsb == 3){
    temperature[7] = '5';
    if(temperature_lsb == 1) temperature[6] = '2';
    else                     temperature[6] = '7';
  }
  temperature[8]  = 223;                         // Degree symbol
  lcd_gotoxy(11, 1);                             // Go to column 10 row 1
  printf(lcd_putc, temperature);                 // Display temperature
  lcd_gotoxy(21, 1);                             // Go to column 1 row 3
  printf(lcd_putc, alarm1);                      // Display alarm1
  lcd_gotoxy(38, 1);                             // Go to column 18 row 3
  if(alarm1_status)  lcd_putc("ON ");            // If A1IE = 1 print 'ON'
  else               lcd_putc("OFF");            // If A1IE = 0 print 'OFF'
  lcd_gotoxy(21, 2);                             // Go to column 1 row 4
  printf(lcd_putc, alarm2);                      // Display alarm2
  lcd_gotoxy(38, 2);                             // Go to column 18 row 4
  if(alarm2_status)  lcd_putc("ON ");            // If A2IE = 1 print 'ON'
  else               lcd_putc("OFF");            // If A2IE = 0 print 'OFF'
  
}
void calendar_display(){                         // Display calendar function
  switch(day){
    case 1:  strcpy(calendar, "Sun   /  /20  "); break;
    case 2:  strcpy(calendar, "Mon   /  /20  "); break;
    case 3:  strcpy(calendar, "Tue   /  /20  "); break;
    case 4:  strcpy(calendar, "Wed   /  /20  "); break;
    case 5:  strcpy(calendar, "Thu   /  /20  "); break;
    case 6:  strcpy(calendar, "Fri   /  /20  "); break;
    case 7:  strcpy(calendar, "Sat   /  /20  "); break;
    default: strcpy(calendar, "Sat   /  /20  "); break;
  }
  calendar[13] = year  % 10 + 48;
  calendar[12] = year  / 10 + 48;
  calendar[8]  = month % 10 + 48;
  calendar[7]  = month / 10 + 48;
  calendar[5]  = date  % 10 + 48;
  calendar[4]  = date  / 10 + 48;
  lcd_gotoxy(1, 2);                              // Go to column 1 row 2
  printf(lcd_putc, calendar);                    // Display calendar
}
void DS3231_display(){
  // Convert BCD to decimal
  second = (second >> 4) * 10 + (second & 0x0F);
  minute = (minute >> 4) * 10 + (minute & 0x0F);
  hour = (hour >> 4) * 10 + (hour & 0x0F);
  date = (date >> 4) * 10 + (date & 0x0F);
  month = (month >> 4) * 10 + (month & 0x0F);
  year = (year >> 4) * 10 + (year & 0x0F);
  // End conversion
  time[7]     = second % 10  + 48;
  time[6]     = second / 10  + 48;
  time[4]     = minute % 10  + 48;
  time[3]     = minute / 10  + 48;
  time[1]     = hour   % 10  + 48;
  time[0]     = hour   / 10  + 48;
  calendar_display();                            // Call calendar display function
  lcd_gotoxy(1, 1);                              // Go to column 1 row 1
  printf(lcd_putc, time);                        // Display time
}
void blink(){
  int8 j = 0;
  while(j < 10 && (input(PIN_B3) || i >= 5) && input(PIN_B4) && (input(PIN_B5) || i < 5)){
    j++;
    delay_ms(25);
  }
}
int8 edit(parameter, x, y){
  while(!input(PIN_B3) || !input(PIN_B5));       // Wait until button RB0 is released
  while(TRUE){
    while(!input(PIN_B4)){                       // If button RB2 is pressed
      parameter++;
      if(((i == 0) || (i == 5)) && parameter > 23)    // If hours > 23 ==> hours = 0
        parameter = 0;
      if(((i == 1) || (i == 6)) && parameter > 59)    // If minutes > 59 ==> minutes = 0
        parameter = 0;
      if(i == 2 && parameter > 31)               // If date > 31 ==> date = 1
        parameter = 1;
      if(i == 3 && parameter > 12)               // If month > 12 ==> month = 1
        parameter = 1;
      if(i == 4 && parameter > 99)               // If year > 99 ==> year = 0
        parameter = 0;
      if(i == 7 && parameter > 1)                // For alarms ON or OFF (1: alarm ON, 0: alarm OFF)
        parameter = 0;
      lcd_gotoxy(x, y);
      if(i == 7){                                // For alarms ON & OFF
        if(parameter == 1)  lcd_putc("ON ");
        else                lcd_putc("OFF");
      }
      else
        printf(lcd_putc,"%02u", parameter);      // Display parameter
      if(i >= 5){
        DS3231_read();                           // Read data from DS3231
        DS3231_display();                        // Display DS3231 time and calendar
      }
      delay_ms(200);                             // Wait 200ms
    }
    lcd_gotoxy(x, y);                            // Go to LCD x coloumn and y row
    lcd_putc("  ");                              // Print two spaces
    if(i == 7) lcd_putc(" ");                    // Print space (for alarms ON & OFF)
    blink();                                     // Call blink function
    lcd_gotoxy(x, y);                            // Go to LCD x coloumn and y row
    if(i == 7){                                  // For alarms ON & OFF
      if(parameter == 1)  lcd_putc("ON ");
      else                lcd_putc("OFF");
    }
    else
      printf(lcd_putc,"%02u", parameter);        // Display parameter
    blink();
    if(i >= 5){
      DS3231_read();
      DS3231_display();}
    if((!input(PIN_B3) && i < 5) || (!input(PIN_B5) && i >= 5)){
      i++;                                       // Increament 'i' for the next parameter
      return parameter;                          // Return parameter value and exit
    }
  }
}
void main(){
  setup_oscillator(OSC_8MHZ);                    // Set internal oscillator to 8MHz
  output_low(PIN_B6);
  output_drive(PIN_B6);                          // Configure pin RB6 as output
  set_tris_d(0);                                 // Configure PORTD pins as outputs
  port_b_pullups(TRUE);                          // Enable PORTB internal pull-ups
  enable_interrupts(GLOBAL);                     // Enable global interrupts
  enable_interrupts(INT_EXT2_H2L);               // Enable external interrupt with edge from high to low
  lcd_init();                                    // Initialize LCD module
  lcd_putc('\f');                                // LCD clear
  while(TRUE){
    if(!input(PIN_B3)){                          // If RB1 button is pressed
      i = 0;
      hour   = edit(hour, 1, 1);
      minute = edit(minute, 4, 1);
      while(!input(PIN_B3));                     // Wait until button RB0 released
      while(TRUE){
        while(!input(PIN_B4)){                   // If button RB2 button is pressed
          day++;                                 // Increment day
          if(day > 7) day = 1;
          calendar_display();                    // Call display calendar
          lcd_gotoxy(1, 2);                      // Go to column 1 row 2
          printf(lcd_putc, calendar);            // Display calendar
          delay_ms(200);
        }
        lcd_gotoxy(1, 2);                        // Go to column 1 row 2
        lcd_putc("   ");                         // Print 3 spaces
        blink();
        lcd_gotoxy(1, 2);                        // Go to column 1 row 2
        printf(lcd_putc, calendar);              // Print calendar
        blink();                                 // Call blink function
        if(!input(PIN_B3))                       // If button RB1 is pressed
          break;
      }
      date = edit(date, 5, 2);                   // Edit date
      month = edit(month, 8, 2);                 // Edit month
      year = edit(year, 13, 2);                  // Edit year
      // Convert decimal to BCD
      minute = ((minute / 10) << 4) + (minute % 10);
      hour = ((hour / 10) << 4) + (hour % 10);
      date = ((date / 10) << 4) + (date % 10);
      month = ((month / 10) << 4) + (month % 10);
      year = ((year / 10) << 4) + (year % 10);
      // End conversion
      // Write time & calendar data to DS3231 RTC
      i2c_start();                               // Start I2C protocol
      i2c_write(0xD0);                           // DS3231 address
      i2c_write(0);                              // Send register adderss (seconds address)
      i2c_write(0);                              // Reset sesonds and start oscillator
      i2c_write(minute);                         // Write minute value to DS3231
      i2c_write(hour);                           // Write hour value to DS3231
      i2c_write(day);                            // Write day value
      i2c_write(date);                           // Write date value to DS3231
      i2c_write(month);                          // Write month value to DS3231
      i2c_write(year);                           // Write year value to DS3231
      i2c_stop();                                // Stop I2C
      delay_ms(200);                             // Wait 200ms
    }
    if(!input(PIN_B5)){                          // If RB3 button is pressed
      while(!input(PIN_B5));                     // Wait until button RB3 released
      i = 5;
      alarm1_hour   = edit(alarm1_hour, 25, 1);
      alarm1_minute = edit(alarm1_minute, 28, 1);
      alarm1_status = edit(alarm1_status, 38, 1);
      i = 5;
      alarm2_hour   = edit(alarm2_hour, 25, 2);
      alarm2_minute = edit(alarm2_minute, 28, 2);
      alarm2_status = edit(alarm2_status, 38, 2);
      alarm1_minute = ((alarm1_minute / 10) << 4) + (alarm1_minute % 10);
      alarm1_hour   = ((alarm1_hour / 10) << 4) + (alarm1_hour % 10);
      alarm2_minute = ((alarm2_minute / 10) << 4) + (alarm2_minute % 10);
      alarm2_hour   = ((alarm2_hour / 10) << 4) + (alarm2_hour % 10);
      // Write alarms data to DS3231
      i2c_start();                               // Start I2C
      i2c_write(0xD0);                           // DS3231 address
      i2c_write(7);                              // Send register address (alarm1 seconds)
      i2c_write(0);                              // Write 0 to alarm1 seconds
      i2c_write(alarm1_minute);                  // Write alarm1 minutes value to DS3231
      i2c_write(alarm1_hour);                    // Write alarm1 hours value to DS3231
      i2c_write(0x80);                           // Alarm1 when hours, minutes, and seconds match
      i2c_write(alarm2_minute);                  // Write alarm2 minutes value to DS3231
      i2c_write(alarm2_hour);                    // Write alarm2 hours value to DS3231
      i2c_write(0x80);                           // Alarm2 when hours and minutes match
      i2c_write(4 | alarm1_status | (alarm2_status << 1));      // Write data to DS3231 control register (enable interrupt when alarm)
      i2c_write(0);                              // Clear alarm flag bits
      i2c_stop();                                // Stop I2C
      delay_ms(200);                             // Wait 200ms
    }
    if(!input(PIN_B4) && input(PIN_B6)){         // When button B2 pressed with alarm (Reset and turn OFF the alarm)
      output_low(PIN_B6);                        // Turn OFF the alarm indicator
      i2c_start();                               // Start I2C
      i2c_write(0xD0);                           // DS3231 address
      i2c_write(0x0E);                           // Send register address (control register)
      // Write data to control register (Turn OFF the occurred alarm and keep the other as it is)
      i2c_write(4 | (!bit_test(status_reg, 0) & alarm1_status) | ((!bit_test(status_reg, 1) & alarm2_status) << 1));
      i2c_write(0);                              // Clear alarm flag bits
      i2c_stop();                                // Stop I2C
    }
    DS3231_read();                               // Read time and calendar parameters from DS3231 RTC
    alarms_read_display();                       // Read and display alarms parameters
    DS3231_display();                            // Diaplay time & calendar
    delay_ms(50);                                // Wait 50ms
  }
}
// End of code
Video:
After connecting the circuit and burning the HEX file into the MCU, I got the result shown similar to what's in the video below where the used microcontroller is PIC16F877A.