SHARPIR.cpp

00001 /* mbed SHARPIR distance sensor
00002  * Copyright (c) 2010 Tomas Johansen
00003  *
00004  * Permission is hereby granted, free of charge, to any person obtaining a copy
00005  * of this software and associated documentation files (the "Software"), to deal
00006  * in the Software without restriction, including without limitation the rights
00007  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00008  * copies of the Software, and to permit persons to whom the Software is
00009  * furnished to do so, subject to the following conditions:
00010  *
00011  * The above copyright notice and this permission notice shall be included in
00012  * all copies or substantial portions of the Software.
00013  *
00014  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00015  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00016  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00017  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00018  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00019  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00020  * THE SOFTWARE.
00021  */
00022 
00023 
00024 #include "mbed.h"
00025 #include "SHARPIR.h"
00026 
00027 
00028 /* This function is currently only working for the Sharp GP2Y0A02YK0F sensor
00029  * which measures from around 20cm to 150cm. To adapt this to other Sharp IR 
00030  * sensors, you have to calculate the variables reg and exp.
00031  * 
00032  * To quickly calculate reg and exp, use microsoft excel to plot the graph 
00033  * provided in the datasheet. You should create a scatterplot (except that 
00034  * the y-axis is [cm], and x-axis is [V]).
00035  *
00036  * When you get the values, right click the line in the graph and select 
00037  * "Add Trendline". Select "power". Also, in the trendline options, check 
00038  * that you want to see the function. It will then be printed in your 
00039  * scatterplot.
00040  *
00041  * This is the function: Reg*x^exp.
00042  *
00043  *
00044  * Example:
00045  *
00046  * SHARPIR sensor(p20);
00047  * sensor.calibrate(57.373, 1.3166, 0.45, 2.5);
00048  * while(1){
00049  *     serial.printf("cm: %f ", sensor.cm()); 
00050  *     wait_ms(50);
00051  * }
00052  *
00053  * You can also use this method to manually plot values you've measured with 
00054  * the "volt" function, which in the end should give a result similar to the 
00055  * values provided below.
00056  *
00057  * Feel free to contact me with improvements for the source code, and
00058  * especially for values that would work for other sensors.
00059  */
00060 
00061 
00062 SHARPIR::SHARPIR(PinName AnalogPort)
00063         : _analogin(AnalogPort) {
00064     higherrange=2.5;
00065     lowerrange=0.45;
00066     reg=57.373; //60.495
00067     exp=-1.3166; //-1.1904
00068 }
00069 
00070 void calibrate(double reg, float exp, double lowerrange, double higherrange) { //sets new reg and exp value
00071 }
00072 
00073 float SHARPIR::volt() {
00074     return(_analogin.read()*3.3); //analogin function returns a percentage which describes how much of 3.3v it's reading, therefor multiply it by 3,3 to get the correct analogin voltage.
00075 }
00076 
00077 float SHARPIR::cm() {
00078     float v;
00079     v=volt();
00080     if (v>higherrange) //sensor is out of higher range
00081         return(reg*pow(v, exp));//0
00082     else if (v<lowerrange)
00083         return(-1.0); //sensor is out of lower range
00084     else
00085         return(reg*pow(v, exp));
00086 }
00087 
00088 float SHARPIR::inch() {
00089     float v;
00090     v=volt();
00091     if (v>higherrange) //sensor is out of higher range
00092         return(0);
00093     else if (v<lowerrange)
00094         return(-1.0); //sensor is out of range
00095     else
00096         return(0.393700787*reg*pow(v, exp));
00097 }