Ultrasonic distance sensor SRF05

Ultrasonic distance sensor SRF05

The SRF05 is an evolutionary step from the SRF04, and has been designed to increase flexibility, increase range, and to reduce costs still further. As such, the SRF05 is fully compatible with the SRF04. Range is increased from 3 meters to 4 meters. A new operating mode (tying the mode pin to ground) allows the SRF05 to use a single pin for both trigger and echo. When the mode pin is left unconnected, the SRF05 operates with separate trigger and echo pins, like the SRF04. The SRF05 includes a small delay before the echo pulse.

Following example uses one pin mode of SRF05. Code is based on the slightly modified HomeLab library 1.03 ultrasonic_measure function. Example is intended for the ATmega128 controller module and Sensor module (v5).

#include <homelab/delay.h>
#include <homelab/module/lcd_gfx.h>
#include <homelab/timer.h>
#include "homelab/common.h"
#include "homelab/pin.h"
 
#define ULTRASONIC_SPEED_OF_SOUND    33000 // cm/s
 
//SRF05 1 pin mode
pin srf05 = PIN(F,3);
 
//external sensor selection (make sure that the resistor is monted on the RC socket)
pin ext_sensors = PIN(G, 0);
 
 
//////////////////////////// UH measure //////////////
 
unsigned short ultrasonic_measure(pin srf05)
{   
    // Pin setup
    pin_setup_output(srf05);
 
    // Set timer 3 to normal mode
    // with period of F_CPU / 8
    timer3_init_normal(TIMER3_PRESCALE_8);      
 
    // Create trigger pulse
    pin_set(srf05);
 
    // Reset timer
    timer3_overflow_flag_clear();
    timer3_set_value(0);    
 
    // Wait ~10 us
    while (timer3_get_value() < 18) {}
 
    // End trigger pulse
    pin_clear(srf05);
 
    //short delay
    sw_delay_ms(1);
 
    //set the pin as input
    pin_setup_input_with_pullup(srf05);
 
    // Wait for echo start
    while (!pin_get_value(srf05))
    {
        // Timeout ?
        if (timer3_overflow_flag_is_set())
        {
            return 0;
        }
    }
 
    // Reset timer again
    timer3_set_value(0);
 
    // Wait for echo end    
    while (pin_get_value(srf05))
    {
        // Timeout ?
        if (timer3_overflow_flag_is_set())
        {
            return 0;
        }
    }
 
    // Convert time to distance:
    //   distance = timer * (1 / (F_CPU / 8)) * speed / 2
    return (unsigned long)timer3_get_value() *
        ULTRASONIC_SPEED_OF_SOUND / (F_CPU / 4);
}
 
/////////////////////////   Main program  /////////////////////////////
 
int main(void)
{
    int dist;
    char text[16]; 
 
    //set external sensor
    pin_setup_output(ext_sensors); 
    pin_set(ext_sensors);
 
    // LCD init
    lcd_gfx_init();
    lcd_gfx_clear();
 
    while (true)
    {
        //Measure
        dist = ultrasonic_measure(srf05);
 
        //print to LCD
        sprintf(text,"Distance: %d cm",dist);
        lcd_gfx_goto_char_xy(0, 0);
        lcd_gfx_write_string(text);
 
        //0,5 s delay
        sw_delay_ms(50);
 
        //Clear LCD
        lcd_gfx_clear();
    }
}