Measure Distance Using Ultrasonic Sensor

 

URM37 V3.2 Ultrasonic Sensor uses an industrial level AVR processor as the main processing unit. It comes with a temperature correction which is very unique in its class.

Specification
 Power: +5V
Current: <20mA
Working temperature: -10℃～+70℃
Detecting range: 4cm-5m
Resolution: 1cm
Interface: RS232 (TTL), PWM
Servo control: One servo control output
Operating Mode: Serial (PWM) passive control mode; Autonomous Mode; On/OFF Mode
Temperature sensor: 12 bits reading from serial port
Size: 22mm × 51 mm
Weight: 30g

1: +VCC - +5V Power
2: GND - Ground
3: RST - Reset
4: PWM - PWM Output 0－25000US，Every 50US represent 1cm
5: MOTO - Servo control signal output
6: COMP/TRIG
COMP - On/OFF mode, when the detecting distance is smaller than a pre-set value, this pin pulls low.
TRIG - PWM or RS232 trigger pin
7: PWR_ON - Enable pin, enable the sensor when high
8: RXD - RS232,TTL communication
9: TXD - RS232,TTL communication

Circuit Diagram

/***********************************************************\                                                                              * Distance meter using ulrtasonicsensor                                 

*

*  Snesor: URM37 Vs 3.2                                    

*  Microcontroller: 16f877a | Oscillater: 20 Mhz            

*  Used modules: Capture Compare PWM 1 (CCP1)          

*  Display Method: 16x2 LCD                                          

\***********************************************************/

 // LCD module connections

sbit LCD_RS at RB4_bit;

sbit LCD_EN at RB5_bit;

sbit LCD_D4 at RB0_bit;

sbit LCD_D5 at RB1_bit;

sbit LCD_D6 at RB2_bit;

sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;

sbit LCD_EN_Direction at TRISB5_bit;

sbit LCD_D4_Direction at TRISB0_bit;

sbit LCD_D5_Direction at TRISB1_bit;

sbit LCD_D6_Direction at TRISB2_bit;

sbit LCD_D7_Direction at TRISB3_bit;

unsigned tOld, tNew;

char edge = 0;

char capture = 0;

unsigned tword;

unsigned distance;

int i;

//Functions

void interrupt();

char int_to_char(int key_n);

//main function

void main() {

  int no1,no2;

  char display[7];

  char display1[7];

  Lcd_Init();                        // Initialize LCD

  Lcd_Cmd(_LCD_CLEAR);               // Clear display

  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

  TRISC = 0;        // assign PORTC as output

  TRISC.B2 = 1;     // RC2 must be input

  T1CON = 0x1;      // Timer1 ON, internal clock Fosc/4

  INTCON.GIE = 1;   //Inable Global Interrupts

  INTCON.PEIE =1;   //Enable Peripheral Interrupts

  PIE1.CCP1IE = 1;  // enable interrupt capture

  TRISD=0;

  PORTD=0;

  CCP1CON = 0x04;   // Capture mode every falling edge

  Lcd_Out(1,1,"   Measure the    ");

  Lcd_Out(2,1," distance  using  ");

  Delay_ms(2000);

  Lcd_Out(1,1,"   Ultrasonic     ");

  Lcd_Out(2,1,"     Sensor       ");

  Delay_ms(2000);

  Lcd_Cmd(_LCD_CLEAR);

  Delay_ms(3000);

  Lcd_Out(1,1,"Distance is:");       //Display Charactors on the LCD

 while(1){       //Start never ending while loop

  if(capture){

  PIE1.CCP1IE = 0; // disable interrupt while processing

  capture = 0;     // clear flag

  // Calculate length of pulse from rising edge to rising edge

  tword = ~tOld + tNew+1;

  // tword contain length of pulse in micro second

  distance=tword /50;      // 50 us = 1cm

  distance=distance/5;

  /* Here IntToStr function has not used to convert intiger numbers to string (Only string can display on LCD). */

  /* Therefore user defined int_to_char function has used                                                       */

  no1=distance%10;

  no2=distance/10;

  for(i=2;i<=4;i++){

  display[i]=int_to_char(no1);

  no1=no2%10;

  no2=no2/10;

  }

  display[5]=int_to_char(no1);

  //Display distance on the LCD (This can be simply relaced by a forloop)

  Lcd_Chr(2,6,display[5]);

  Lcd_Chr(2,7,display[4]);

  Lcd_Chr(2,8,display[3]);

  Lcd_Chr(2,9,display[2]);

  Lcd_Chr(2,11,'c');

  Lcd_Chr(2,12,'m');

  PIR1.CCP1IF = 0; // clear CCP flag

  PIE1.CCP1IE = 1; // enable interrupt

 }

}// End of while

} // End of main

void interrupt() {

if(PIR1.CCP1IF==1){          //Check CCP1 enterrupt

if(!edge){

tOld = (256*CCPR1H)+CCPR1L; // keep starting value

edge = 1;

PIE1.CCP1IE = 0;            // disable interrupt for change

CCP1CON = 0x05;             // Capture mode every rising edge edge

PIE1.CCP1IE = 1;            // Enable interrupt capture

}else{

tNew = (256*CCPR1H)+CCPR1L; // Keep ending value

capture = 1;                // Complete capture, set a flag

edge = 0;

PIE1.CCP1IE = 0;           // disable interrupt for change

CCP1CON = 0x04;            // Capture mode every falling edge

PIE1.CCP1IE = 1;           // Enable interrupt capture

}

PIR1.CCP1IF = 0; //Clear CCP flag

}

}

 //Function to convert integer values to char

 char int_to_char(int key_n){

           char key_c_n[1];

           if(key_n==0){

           key_c_n[0]='0';

           } else if(key_n==1){

           key_c_n[0]='1';

           } else if(key_n==2){

           key_c_n[0]='2';

           } else if(key_n==3){

           key_c_n[0]='3';

           } else if(key_n==4){

           key_c_n[0]='4';

           } else if(key_n==5){

           key_c_n[0]='5';

           } else if(key_n==6){

           key_c_n[0]='6';

           } else if(key_n==7){

           key_c_n[0]='7';

           } else if(key_n==8){

           key_c_n[0]='8';

           } else if(key_n==9){

           key_c_n[0]='9';

           }

           return key_c_n[0];

           }  //End of the function