Ultrasonic Distance Module HC-SR04

[NickE]

Version: 1
Status: Beta
License: GPL

The Ultrasonic Distance Module HC-SR04 is popular with hobbyist for obstacle avoidance and ranging.  It is commonly used with the Arduino.  I have used it with the Arduino and with the RaspberryPi.
I recently received the startKIT and was looking a quick learning project for intefacing with sensors.  So, after soldering all the header pins, I connected up the HC-SR04.  The below sample code runs fine in the xTIMEcomposer Studio.
/* Quick test for using the HC-SR04 Ultrasonic Distance Sensor

 * HC-SR04 is a 5V device

 * Used a voltage divider on Echo to bring down to 3.3V

 * app_HC-SR04.xc

 *

 *  Created on: Jan 5, 2014

 *      Author: NickE

 */

#include <xs1.h>

#include <timer.h>

#include <stdio.h>



in  port  inP = XS1_PORT_1I;                            //Echo - Pin D24

out port outP = XS1_PORT_1O;                            //Trigger - Pin D25



int echo_time(void){

    timer t;                                            //10ns increments

    unsigned int start_time,stop_time;



    outP <: 0;                                          //make sure is low

    delay_milliseconds(50);



    //trigger pulse

    outP <: 1;

    delay_microseconds(10);                             //datasheet indicate minimum of 2us

    outP <: 0;



    //wait for echo

    inP when pinseq(0x1) :> void;                       //rising edge of echo - will wait forever

    t :> start_time;

    inP when pinseq(0x0) :> void;                       //falling edge of echo - will wait forever

    t :> stop_time;



    return (stop_time - start_time);                    //elapsed 10ns timer ticks

}



int main(void){

    unsigned int elapsed;

    float dist_cm;



    while (1)

    {

        elapsed = echo_time();

        dist_cm = (float)elapsed * 0.000170145;             //speed of sound 340.29 m/s - divide by 2 for round trip

        printf("Distance %0.2f cm, %0.2f in, %0.2f ft\n",dist_cm,dist_cm/2.54,dist_cm/30.48);

        delay_milliseconds(250);

    }

    return 0;

}

 
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