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ultrasonic range finder

 
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aasief



Joined: 12 Feb 2009
Posts: 12
Location: cape town

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ultrasonic range finder
PostPosted: Wed Apr 29, 2009 6:22 am     Reply with quote
Could someone tell me whats wrong with this code
Code:


#include "16f877.h"
#use delay(clock=4000000)
#define use_portb_lcd
#include "lcd.c"
#int_ccp1

unsigned int time;
void main()
{   int x;
   
    lcd_init();

   while(1)
  {
    output_low(pin_a5);
    setup_ccp1(ccp_capture_re);
    setup_timer_1(t1_internal);
    for(x=0;x<5;x++)
    {
   output_high(pin_d2);
   delay_us(90);
   output_low(pin_d2);
   delay_us(25);
   }
   delay_us(1000);
    output_high(pin_a5);
    enable_interrupts(global);
    enable_interrupts(int_ccp1);
    delay_ms(60);
   
  }
}   

void isr_ccp1()
{
   time=ccp_1;
   printf(lcd_putc"t=%5u  ",time);
   set_timer1(0);
   clear_interrupt(int_ccp1);
   
}
bungee-



Joined: 27 Jun 2007
Posts: 206

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PostPosted: Wed Apr 29, 2009 7:43 am     Reply with quote
This code need some serious rewriting. Couple of years I wrote similar program for the 16F84A in the assembly.

At the first glimpse your frequency is not 40kHz. I suppose that you use 40kHz ultrasound transmiter/receiver pair. Your code transmits at ~ 8,7kHz.

Here is the flow how you should do this:

Code:

           Init the PIC
                |
                |
       Send ping (8 pulses at 40kHz) <---------+
          Set timer1 to 0                      |
                |                              |
                |                              |
        Delay (see comment *)                  |
                |                              |
                |                              |
        Check if pong received <--------+      |
                |                       |      |
                +----- NO --------------+      |
                |                              |
        Calculate distance from time           |
                |                              |
                |                              |
          Display distance                     |
                |                              |
                |                              |
                +------------------------------+


* Delay is used because first reply is not the correct one. Determine that based on experience.
aasief



Joined: 12 Feb 2009
Posts: 12
Location: cape town

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PostPosted: Thu Apr 30, 2009 5:06 am     Reply with quote
Thanx for ur response.

The delays I'm using are correct because I get 38.7 kHz out. I don't know why I do because looking at it, the PIC isn't doing what it's supposed to be doing.
I'm having a problem with capturing the pulse. I am getting a received pulse and I measured it and I get the correct time delay for distance measured.
I suspect that whatever is making my delays not work, is the same thing that's making my capture not work. Is there something wrong with my void isr loop ?

Thanx
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