David Glover / HCSR04

hcsr04.h@2:d99d91a7e8f1, 2012-03-22 (annotated)

Committer:
dglover77
Date:
Thu Mar 22 05:49:41 2012 +0000
Revision:
2:d99d91a7e8f1
Parent:
1:c7753ec66a4b 
Updated comments

Who changed what in which revision?

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dglover77 2:d99d91a7e8f1 1 // Primary Author: David Glover
dglover77 2:d99d91a7e8f1 2 // March, 2012
dglover77 2:d99d91a7e8f1 3 // ECE 510 Embedded Systems, Roy Kravitz
dglover77 2:d99d91a7e8f1 4 //
dglover77 0:c587e0d5adda 5 // HCSR04 ultrasonic sensor class using interrupts and allowing multiple instances.
dglover77 0:c587e0d5adda 6 // You can use the same trigger pin for multiple instances, the echo is recieved and
dglover77 0:c587e0d5adda 7 // measurement calculated based on the echo input alone (when the echo signal goes high
dglover77 2:d99d91a7e8f1 8 // the timer is started, when the echo signal goes low the timer value in microseconds
dglover77 0:c587e0d5adda 9 // is saved as the length, and the timer is stopped and reset. Length calculation is done
dglover77 0:c587e0d5adda 10 // when the length is requested (either inches or centimeters) using the appropriate
dglover77 0:c587e0d5adda 11 // function.
dglover77 0:c587e0d5adda 12
dglover77 0:c587e0d5adda 13 #ifndef MBED_HCSR04_H
dglover77 0:c587e0d5adda 14 #define MBED_HCSR04_H
dglover77 0:c587e0d5adda 15
dglover77 0:c587e0d5adda 16 //required to use mbed functions
dglover77 0:c587e0d5adda 17 #include "mbed.h"
dglover77 0:c587e0d5adda 18
dglover77 0:c587e0d5adda 19 #define TRIGGER_DELAY 12 // length of trigger signal expected by HCSR04 sensor
dglover77 0:c587e0d5adda 20 #define INCHES_DIVISOR 148 //
dglover77 0:c587e0d5adda 21 #define CM_DIVISOR 58
dglover77 0:c587e0d5adda 22
dglover77 0:c587e0d5adda 23 class hcsr04 {
dglover77 0:c587e0d5adda 24
dglover77 0:c587e0d5adda 25 private:
dglover77 1:c7753ec66a4b 26 InterruptIn *_echo_int; // pin to receive echo signal
dglover77 1:c7753ec66a4b 27 DigitalOut trigger_out; // pin to send the trigger signal
dglover77 1:c7753ec66a4b 28 Timer timer; // timer to track length of pulse
dglover77 1:c7753ec66a4b 29 float value; // to store the last pulse length
dglover77 0:c587e0d5adda 30
dglover77 0:c587e0d5adda 31 public:
dglover77 0:c587e0d5adda 32 bool measuring; // true while the echo signal is high (measurement in progress)
dglover77 1:c7753ec66a4b 33 hcsr04(PinName trigger, PinName echo) : trigger_out(trigger) { // _pass the names to the pin configuration
dglover77 0:c587e0d5adda 34 // _trigger_out = new DigitalOut( trigger );
dglover77 0:c587e0d5adda 35 _echo_int = new InterruptIn( echo );
dglover77 0:c587e0d5adda 36 _echo_int->rise(this, &hcsr04::timer_start);
dglover77 0:c587e0d5adda 37 _echo_int->fall(this, &hcsr04::calc_measurement);
dglover77 0:c587e0d5adda 38 measuring = false;
dglover77 0:c587e0d5adda 39 }
dglover77 0:c587e0d5adda 40
dglover77 0:c587e0d5adda 41
dglover77 2:d99d91a7e8f1 42 void calc_measurement() {
dglover77 2:d99d91a7e8f1 43 value = timer.read_us();
dglover77 2:d99d91a7e8f1 44 //value = timer.read_us() - timestart;
dglover77 2:d99d91a7e8f1 45 timer.stop();
dglover77 2:d99d91a7e8f1 46 timer.reset();
dglover77 2:d99d91a7e8f1 47 measuring = false;
dglover77 2:d99d91a7e8f1 48 }
dglover77 2:d99d91a7e8f1 49
dglover77 2:d99d91a7e8f1 50 void timer_start() {
dglover77 2:d99d91a7e8f1 51 this->timer.start();
dglover77 2:d99d91a7e8f1 52 measuring = true;
dglover77 2:d99d91a7e8f1 53 }
dglover77 2:d99d91a7e8f1 54
dglover77 2:d99d91a7e8f1 55 void trigger(void) {
dglover77 2:d99d91a7e8f1 56 trigger_out.write(1); // start trigger signal
dglover77 2:d99d91a7e8f1 57 wait_us(TRIGGER_DELAY);
dglover77 2:d99d91a7e8f1 58 trigger_out.write(0); // end trigger signal
dglover77 2:d99d91a7e8f1 59 }
dglover77 2:d99d91a7e8f1 60
dglover77 2:d99d91a7e8f1 61 float inches() { // return distance in inches.
dglover77 2:d99d91a7e8f1 62 return value / INCHES_DIVISOR;
dglover77 2:d99d91a7e8f1 63 }
dglover77 2:d99d91a7e8f1 64
dglover77 2:d99d91a7e8f1 65 float cm() { // return distance in centimeters.
dglover77 2:d99d91a7e8f1 66 return value / CM_DIVISOR;
dglover77 2:d99d91a7e8f1 67 }
dglover77 2:d99d91a7e8f1 68
dglover77 0:c587e0d5adda 69 };
dglover77 0:c587e0d5adda 70
dglover77 0:c587e0d5adda 71 #endif