ardupilot/libraries/AP_RangeFinder/RangeFinder.cpp

// -*- tab-width: 4; Mode: C++; c-basic-offset: 3; indent-tabs-mode: t -*-
/*
	AP_RangeFinder.cpp - Arduino Library for Sharpe GP2Y0A02YK0F 
	infrared proximity sensor
	Code by Jose Julio and Randy Mackay. DIYDrones.com

	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 has the basic functions that all RangeFinders need implemented
*/

// AVR LibC Includes
#include "WConstants.h"
#include "RangeFinder.h"

// Constructor /////////////////////////////////////////////////////////////////
RangeFinder::RangeFinder() : _num_averages(AP_RANGEFINDER_NUM_AVERAGES), _ap_adc(NULL)
{
}

// Public Methods //////////////////////////////////////////////////////////////
void RangeFinder::init(int analogPort, AP_ADC *ap_adc)
{
    // local variables
    int i;
	
    // store the analog port to be used
    _analogPort = analogPort;
	
	// set the given analog port to an input
	if( analogPort != AP_RANGEFINDER_PITOT_TUBE ) 
	{
	    pinMode(analogPort, INPUT);
    }else{
	    _num_averages = 0;  // turn off averaging for pitot tube because AP_ADC does this for us
	}
	
	// capture the AP_ADC object if passed in
	if( ap_adc != NULL )
	    _ap_adc = ap_adc;	
	
	// make first call to read to get initial distance
	read();
	
	// initialise history
	for( i=0; i<AP_RANGEFINDER_NUM_AVERAGES; i++ )
	    _history[i] = distance;	
}

void RangeFinder::set_orientation(int x, int y, int z)
{
    orientation_x = x; 
	orientation_y = y; 
	orientation_z = z;
}

// Read Sensor data - only the raw_value is filled in by this parent class
int RangeFinder::read()
{
    // local variables
	int temp_dist;
	int total = 0;	
	int i;

	// read from the analog port or pitot tube
	if( _analogPort == AP_RANGEFINDER_PITOT_TUBE ) {
	    if( _ap_adc != NULL )
	        raw_value = _ap_adc->Ch(AP_RANGEFINDER_PITOT_TUBE_ADC_CHANNEL) >> 2;  // values from ADC are twice as big as you'd expect
	    else
		    raw_value = 0;
	}else{
        // read raw sensor value and convert to distance
        raw_value = analogRead(_analogPort);
	}
	
	// convert analog value to distance in cm (using child implementation most likely)
	temp_dist = convert_raw_to_distance(raw_value);
	
	// ensure distance is within min and max
	distance = constrain(temp_dist, min_distance, max_distance);
	
	// filter the results
	if( _num_averages > 1 ) 
	{
        _history_ptr = (_history_ptr + 1) % _num_averages;
        _history[_history_ptr] = distance;
	    for(i=0; i<_num_averages; i++ )
	        total += _history[i];
        distance = total / _num_averages;	
    }
	
	// return distance
	return distance;
}