sr04.h

//***************************************************************************
//
// file : bmptk/chips/sr04.h
//
// LICENSE (MIT expat license, copy of license.txt)
//
// Copyright (c) 2013 Wouter van Ooijen (wouter@voti.nl)
// 
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE..
//
//***************************************************************************

#pragma once
#ifndef BMPTK_CHIPS_H
#define BMPTK_CHIPS_H

   namespace bmptk {
                   
      //
      //
      template< typename trigger, typename pulse >
      class sr04 {   
      public: 
          
         static void init(){
            trigger::init();
            trigger::set( 0 );
            pulse::init();
         }
        
         //
         static bmptk::time pulse_width_get( 
            bmptk::time error_value = -1 * bmptk::us 
         ){
                 
                  // when the echo line is not silent something is wrong
                  if( pulse::get() ){
               return error_value;
            }                   
                
            // trigger pulse to the sr04
            trigger::set( 1 );
            bmptk::wait( 10 * bmptk::us );
            trigger::set( 0 );
         
            // wait for start of echo pulse from sr04
            bmptk::time t1 = bmptk::current_time();
            while( !pulse::get() ){
               if( ( bmptk::current_time() - t1 ) > ( 1 * bmptk::ms ) ){
                  return error_value;
               }
            }
         
            // wait for end of echo pulse from sr04
            t1 = bmptk::current_time();
            while( pulse::get() ){
               if( ( bmptk::current_time() - t1 ) > ( 20 * bmptk::ms ) ){
                  return error_value;
               }
            } 
      
            // get end time
            bmptk::time t2 = bmptk::current_time();
            
            // debug
            // std::cout << t2 - t1 << " " << bmptk::us << "\n" ; 
            
            // return length of the pulse
            return t2 - t1;
         }
         
         //
         static int distance_mm_get(
            int error_value    = -1,
            int speed_of_sound = 3430  
         ){
            bmptk::time t = pulse_width_get( -1 * bmptk::us ); 
            if( t == ( -1 * bmptk::us )){ 
               return error_value; 
            }
         
            // calculate the distance in mm
            return ( t * speed_of_sound ) / ( 2 * 10000 * bmptk::us );   
         }
            
      }; 


        
   }; // namespace bmptk;         

#endif // #ifndef BMPTK_CHIPS_H