PIC16F84A LCD And HC-SR04 Distance Sensor Using XC8

The SR-HC04 uses sound wave to measure detected object distance. It's simple to use with a small micro-controller especially the Arduino. The controller just trigger a logic high TTL signal to command this sensor to begin the detection. The output signal from this module is a TTL logic high signal that the controller need to measure its duration before distance data can be obtained.

Simulating Program

In this example, I use PIC16F84A to interface with this distance sensor. Detected distance will show on a 16x2 character LCD. The controller uses a 4MHz external crystal oscillator. To measure external input pulse duration precisely we will need to use timer.

SR-HC04 module from manufacturer's Datasheet

 

The micro-controller execution frequency is Fosc/4 that's 4MHz/4 is 1MHz. So its execution time is 1µs. PIC16F84A has one timer module - Timer 0. This timer is automatically increment is count register for every execution of micro-controller instruction with an appropriate clock pre-scaler. I need to make a 1:1 pre-scaler to get a 1µs timing unit.

Timing Diagram

The detected distance can be obtained by is formula,

Distance (in cm) = High Level TTL Signal (in µs) / 58.

Using MPLABX IDE and XC8 compiler to write this program is pretty easy.

 
#include <xc.h>
#include "LCD4Bits.h"
 
// PIC16F84A Configuration Bit Settings
// CONFIG
#pragma config FOSC = XT        // Oscillator Selection bits (XT oscillator)
#pragma config WDTE = OFF        // Watchdog Timer (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (Power-up Timer is disabled)
#pragma config CP = OFF         // Code Protection bit (Code protection disabled)
 
#define _XTAL_FREQ  4000000UL
#define TRIGGER     RA1
#define ECHO        RA0
 
volatile uint8_t T0OV=0;
volatile uint16_t myCounter=0;
 
void interrupt T0_ISR(void){
    if(T0IF){
        T0OV+=1;
        myCounter++;
        T0IF=0;
    }
}
 
uint16_t getDistance=0,temp=0;
void readDistance(void){
    TRIGGER=1;
    __delay_us(10);
    TRIGGER=0;
    __delay_us(30);
    while(ECHO==0){
        /*Waiting For High Pulse Response, Or Sensor Present*/
        temp++;
        __delay_us(10);
        if(temp>=20) break;
    }
    TMR0=0;
    T0OV=0;
    while(ECHO==1);
    temp=(T0OV<<8)+TMR0+20;
    getDistance=temp/58;
 
    lcdXY(8,2);
    if(temp>=10000) lcdData(48+temp/10000);        else lcdData(' ');
    if(temp>=1000)  lcdData(48+(temp%10000)/1000); else lcdData(' ');
    if(temp>=100)   lcdData(48+(temp%1000)/100);   else lcdData(' ');
    if(temp>=10)    lcdData(48+(temp%100)/10);     else lcdData(' ');
    lcdData(48+temp%10);
 
    lcdData(' ');
    lcdData(228);
    lcdData('S');
 
    lcdXY(8,1);
    if(temp>=116&&getDistance<=400){
        if(getDistance>=100) lcdData(48+getDistance/100);      else lcdData(' ');
        if(getDistance>=10)  lcdData(48+(getDistance%100)/10); else lcdData(' ');
        lcdData(48+getDistance%10);
 
        temp = temp%58;
        temp=(temp*100)/58;
        lcdData('.');
        lcdData(48+(temp%100)/10);
        lcdData(48+temp%10);
        lcdData('c');
        lcdData('m');
    }
    else lcdString("Invalid ");
 
    temp=0;
    T0OV=0;
    TMR0=0;
}
 
int main(void){
 
    PORTA=0;
    TRISA=0x01;
 
    PORTB=0;
    TRISB=0;
    T0CS=0;
    PSA=1;
    OPTION_REGbits.PS=0;
    T0IE=1;
    GIE=1;
    T0IF=0;
 
    lcdInit();
    lcdXY(5,1);
    lcdString("PIC16F84A");
    lcdXY(2,2);
    lcdString("HC-SR04 Example");
    __delay_ms(2000);
    lcdCommand(CLEAR_SCREEN);
    __delay_ms(3);
    lcdString("Range: ");
    lcdXY(1,2);
    lcdString("Time : ");
    TMR0=0;
 
    while(1){
        if(myCounter>=5000){
            readDistance();
            myCounter=0;
        }
    }
    return 0;
}

 

This program requires a little amount of micro-controller resource. Click here to download its source file. We can also use a multiplexing 7-Segment display for better viewing.