PIC16F84A Simple Frequency Meter With LCD Using XC8

Frequency meter can be made using a conventional digital ICs with a big size, and complicated circuit connection. A small 8-bit micro-controller could do this job using a low level Assembly language or even a higher level C language.

In this example, I use an 8-bit PIC16F84A micro-controller to count external TTL input pulse. The total count will update for every seconds.

Simulating Program

I use RA4/T0CKI (Timer0 External Clock Input) pin to count external TTL pulse. Since Timer0 is only 8-bit wide the maximum counting is only 255 counts. So I add Timer0 Interrupt to increase the maximum counts. I use XC8 built-in delay function to create a precise 1000 ms (1 second) delay before the summation of external pulse is evaluated. A 16x2 character LCD is suitable for this example.

#include <stdio.h>
#include <xc.h>
 
#define _XTAL_FREQ 4000000UL
 
#include "LCD4Bits.h"
 
void tmr0Init(void){
    PORTA=0;
    TRISA4=1;
    T0CS=1;
    T0SE=0;
    PSA=1;
    OPTION_REGbits.PS=0;
    T0IE=1;
    GIE=1;
    T0IF=0;
}
 
long TMR0H=0;
 
void interrupt T0_ISR(void){
    if(T0IF){
        TMR0H+=1;
        T0IF=0;
    }
}
 
int main(void){
    unsigned char freq[10];
    uint32_t temp=0;
    PORTB=0;
    TRISB=0;
    lcdInit();
    tmr0Init();
    lcdXY(4,1);
    lcdString("PIC16F84A");
    lcdXY(1,2);
    lcdString("Frequency Meter");
    __delay_ms(1000);
    lcdCommand(CLEAR_SCREEN);
    __delay_ms(5);
    lcdXY(4,1);
    lcdString("Frequency:");
    TMR0H=0;
    TMR0=0;
    while(1){
        __delay_ms(1000);
        temp=(TMR0H<<8)+TMR0;
        lcdXY(6,2);
        sprintf(freq,"%uHz ",temp);
        lcdString(freq);
        TMR0H=0;
        TMR0=0;
    }
    return 0;
} 

I can not test it on bread-board because this chip was burn out. And I only have some newer PIC chips. So this program can only be tested using a simulator like Proteus. We can use another PIC chip like the PIC16F628A, and CCS PICC compiler. 

Resource Usage

 

This program require 69.5% of program memory, and 89.7% of data memory. Click here to download this example.