#include <16F877A.h>
#device ICD=TRUE
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=10000000)
#priority CCP1, TIMER1

#define send_us PIN_D7
#define receive_us PIN_C2

float temp[10] = {0};
float distance;
float avg_dist;
float time;
float us_speed = 345.123;
int1 echo = 0;

#INT_TIMER1
void overflow()
{
   disable_interrupts(GLOBAL);
   clear_interrupt(INT_CCP1);
   clear_interrupt(INT_TIMER1);
   setup_timer_1(T1_DISABLED);
   setup_ccp1(CCP_OFF);
   distance = 512;
}

#INT_CCP1
void receive()
{
   if(!echo)
   {
      disable_interrupts(GLOBAL);
      clear_interrupt(INT_TIMER1);
      clear_interrupt(INT_CCP1);
      setup_ccp1(CCP_OFF);
      setup_timer_1(T1_DISABLED);
      time = (CCP_1) * 0.0000004;
      distance = time * us_speed;
      distance = distance / 2;
      distance -= 0.04;
      echo = 1;
   }
}

void send()
{
   int i = 0;
   //set ccp and timer module
   setup_ccp1(CCP_CAPTURE_RE);
   setup_timer_1 (T1_INTERNAL);
   //all interrupts on
   enable_interrupts(GLOBAL);
   echo = 0;
   output_bit(send_us, 1);
   set_timer1(0);
   delay_us(200);
   output_bit(send_us, 0);
}

void analyze()
{
   int i = 0, cnt_max = 0, max = 0, min = 0, count = 0, dist;
   float cur_sum = 0, cur_dist = 0;
   for(i = 0; i < 10; i++)
   {
      if(temp[i] == 512.0) cnt_max++;
      if(temp[i] > temp[max]) max = i;
      if(temp[i] < temp[min]) min = i;
   }
   if(cnt_max > 6) avg_dist = 255;
   else
   {
      for(i = 0; i < 10; i++)
         if(i != max && i != min && temp[i] != 512.0)
         {
            cur_sum += temp[i];
            count++;
         }
         cur_dist = cur_sum / count;
         cur_dist = cur_dist * 100;
         dist = (int)cur_dist;
         if((cur_dist - dist) >= 0.5) dist++;
         avg_dist = dist;
   }
}
main()
{
   //define variables
   int i = 0, j = 0;
   //set IO ports
   set_tris_b(0x00);
   set_tris_c(0x00);
   set_tris_d(0x00);
   //enable interrupts
   enable_interrupts(INT_TIMER1);
   clear_interrupt(INT_TIMER1);
   enable_interrupts(INT_CCP1);
   clear_interrupt(INT_CCP1);
   //clear IO ports
   output_b(0x00);
   output_c(0x00);
   output_d(0x00);
   for(j = 0; j < 25; j++)
   {
       for(i = 0; i < 10; i++)
      {
         send();
         temp[i] = distance;
         delay_ms(20);
      }
      analyze();  
   }
}