Using Analog Comparator in PIC Microcontroller

Comparator Symbol

Using Analog Comparator in PIC Microcontroller

Comparator Module in PIC

Analog Comparator is a device which compares two voltage signals and switches its output to indicate which one is larger. The analog comparator is used in many applications such as battery charger, analog to digital converters, IR sensors where we need to compare two signals. Most of the PIC Microcontrollers have built in Comparator Module which makes ease of design and saves cost. For demonstration, we use PIC16F877A.

PIC16F877A consists of two analog comparators which can be used in eight different modes. The input pins of comparator are multiplexed with I/O port pins RA0 through RA3 while output pins are multiplexed with RA4 and RA5. CMCON register is the Comparator Module control register.

CMCON Register

CMCON Register of PIC Microcontroller

CMCON Register of PIC Microcontroller

 CM0 – CM2

The Least Significant 3 bits, CM0 – CM2 is used to select one of the eight modes that the comparator module can work.


Mode Selection of Comparator Module in PIC Microcontroller

Mode Selection of Comparator Module in PIC Microcontroller

In normal cases we turn off the comparator module by setting CMCON = 0x07.

C2OUT : Comparator 2 Output bit. It is a read only bit.

 When C2INV = 0 : 

1 = C2Vin+ > C2Vin-
0 = C2Vin+ < C2Vin-



When C2INV = 1:

1 = C2Vin+ < C2Vin-
0 = C2Vin+ > C2Vin-

C1OUT :  Comparator 1 Output bit. It is a read only bit.

When C1INV = 0:



1 = C1Vin+ > C1Vin-
0 = C1Vin+ < C1Vin-

When C1INV = 1:

1 = C1Vin+ < C1Vin-
0 = C1Vin+ > C1Vin-

C2INV : Comparator 2 Output Inversion Bit. When this bit is set the Comparator 2 output will be inverted.

C1INV :  Comparator 1 Output Inversion Bit. When this bit is set the Comparator 1 output will be inverted.

For the demonstration of the working of Comparator Module in PIC Microcontroller, we use the mode ‘Two Common Reference Comparators with Output’.

Circuit Diagram

Using Analog Comparator in PIC Microcontroller Circuit Diagram

Using Analog Comparator in PIC Microcontroller Circuit Diagram

Note: VDD and VSS of the pic microcontroller is not shown in the circuit diagram. VDD should be connected to +5V and VSS to GND.

In this example we are comparing voltages across two LDRs (Light Dependent Resistors) with reference voltage set by the variable resistor RV1.  LED will glow if the voltage across LDR is less than the reference voltage. LEDs D1 and D2 are supplied directly from the output of comparator. Note that  RA4 is an open collector I/O pin, so when used as an output, a pull-up resistor is required. LEDs D3 and D4 are supplied from PORTC, which is powered through program.

MikroC Program

void main()
{ 
  TRISC = 0; //Configure PORTC as ouput

  TRISA.RA0=1; // Configure as input pin for negative input of Comparator 1
  TRISA.RA1=1; // Configure as input pin for negative input of Comparator 2
  TRISA.RA2=1; // Configure as input pin for positive input of Comparator 1
  TRISA.RA3=1; // Configure as input pin for positive input of Comparator 2
  TRISA.RA4=0; // Configure as output pin for output of Comparator 1
  TRISA.RA5=0; // Configure as output pin for output of Comparator 2

  CMCON=0x05; // 'Two Common Reference Comparators with Outputs' Mode

  while(1)
  {
    PORTC.F0 = CMCON.C2OUT; // Assigning output of comparator 2 to RC0
    PORTC.F1 = CMCON.C1OUT; // Assigning output of comparator 2 to RC1
    Delay_ms(100);
  }
}

Download Here

You can download the hex file, MikroC source code, Proteus files etc here…

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  • Justin

    Thank u………………

  • joesph

    i am designing three phase automatic changeover with comparator that compare the three phase. i am using pic micro controller. i need your help. thanks

  • What is your doubt??

  • sanjeewa

    how to do pin of pic16f877a output ? from assembly lan.

  • Sy Hoa

    comparator module by mikroelectronic. Help me! Thanks

  • Selva Prakash Ksm

    hii if i want to get indication from C1OUT in 011 mode what is the programe for it

  • Selva Prakash Ksm

    #include
    void main()
    {
    TRISA0=1;
    TRISA1=1;
    TRISA4=0;
    PORTA=0X00;
    CMCON=0X43;
    if(C1OUT)
    {
    RA4=1;
    }
    else
    RA4=0;
    }
    correct it pls

  • Please explain what is the problem you are facing.

    Kindly use our forums ( https://electrosome.com/forums/ ) for asking doubts outside the scope of above article.

  • You can change the CMCON register for that.

  • Just use CMCON=0X0B; as you mentioned 011 mode in the below comment.. B = 1011