Author Topic: problem with arduino programming  (Read 1385 times)

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Offline sumitprakashTopic starter

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problem with arduino programming
« on: March 28, 2013, 02:09:58 PM »
regarding problem with ultrasonic sensor(HC-SR04)

i am making a robot to reach its destination avoiding obstacle.
i am using HC-SR04. My problem is when the object is near loop runs faster and when object is far loop runs slower.
my further programming is based on counting the loops in given time.

since, rate of counting the loops is not constant, i am having trouble.

i have made some changes in pulseIn() function  to delay the loop when object is near but its not working.

here is the code for pulseIn() function:
Please reply as soon as possible.

  wiring_pulse.c - pulseIn() function
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $

#include "wiring_private.h"
#include "pins_arduino.h"

unsigned long numloops;
unsigned long maxloops;
unsigned long width;

/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
 * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
 * to 3 minutes in length, but must be called at least a few dozen microseconds
 * before the start of the pulse. */
unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
   // cache the port and bit of the pin in order to speed up the
   // pulse width measuring loop and achieve finer resolution.  calling
   // digitalRead() instead yields much coarser resolution.
   uint8_t bit = digitalPinToBitMask(pin);
   uint8_t port = digitalPinToPort(pin);
   uint8_t stateMask = (state ? bit : 0);
   width = 0;  // keep initialization out of time critical area

   // convert the timeout from microseconds to a number of times through
   // the initial loop; it takes 16 clock cycles per iteration.
   numloops = 0;
   maxloops = microsecondsToClockCycles(timeout) / 16;
   // wait for any previous pulse to end
   while ((*portInputRegister(port) & bit) == stateMask)
      if (numloops++ == maxloops)
   // wait for the pulse to start
   while ((*portInputRegister(port) & bit) != stateMask)
      if (numloops++ == maxloops)
   // wait for the pulse to stop
   while ((*portInputRegister(port) & bit) == stateMask) {
      if (numloops++ == maxloops)

   // convert the reading to microseconds. The loop has been determined
   // to be 20 clock cycles long and have about 16 clocks between the edge
   // and the start of the loop. There will be some error introduced by
   // the interrupt handlers.
      return clockCyclesToMicroseconds(width * 21 + 16);
      return clockCyclesToMicroseconds(numloops * 21 + 16);
« Last Edit: March 28, 2013, 02:18:35 PM by sumitprakash »

Offline jwatte

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Re: problem with arduino programming
« Reply #1 on: March 28, 2013, 10:09:16 PM »
You can decide to always run the loop slowly. Then, delay at the end of the loop until the loop duration is what the maximum value should be.

Or you can re-write the code to use pin change interrupts to record on/off times for the pulse. There will be some slight inaccuracy because of other interrupts (used to run "millis()" and similar functions) but it will in general work OK.

Offline sumitprakashTopic starter

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Re: problem with arduino programming
« Reply #2 on: March 29, 2013, 10:55:06 AM »
ok :)
thanks :)


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