TSL2550.cpp

00001 /*
00002  * mbed library to use a TAOS TSL2550 Ambient Light Sensor
00003  * Copyright (c) 2011 Stefan Goeckeritz, 
00004  * RheinAhrCampus Remagen, Suedallee 2, 53424 Remagen
00005  * 
00006  * Released under the MIT License: http://mbed.org/license/mit
00007  */
00008 
00009 #include "mbed.h"
00010 #include "TSL2550.h"
00011 
00012 #define TSL2550_ADDR 0x72                                                     //hardwired slave address of TSL2550
00013 #define xpow(x, y) ((long)1 << y)
00014 
00015 
00016 TSL2550::TSL2550 (PinName p_sda, PinName p_scl ) : i2c(p_sda, p_scl) {
00017     init();
00018 }
00019 
00020 TSL2550::TSL2550 (I2C& p_i2c) : i2c(p_i2c) { 
00021     init();
00022 }
00023 
00024 unsigned short  TSL2550::get_ch0() {
00025     return ch0;
00026 }
00027 
00028 unsigned short TSL2550::get_ch1() {
00029     return ch1;
00030 }
00031 
00032 double TSL2550::get_lux() {
00033     return lux;
00034 }
00035 
00036 void TSL2550::update () {
00037     unsigned short c0, c1, s0, s1;
00038     int adc0, adc1;
00039     double r;
00040 
00041     //read channel 0 and 1
00042     ch0 = twi_read(TSL2550_ADDR, 0x43);
00043     wait(0.5);
00044     ch1 = twi_read(TSL2550_ADDR, 0x83);
00045 
00046     //now compute lux value, if data is valid
00047     if((ch0 & 0x80) &&  (ch1 & 0x80))
00048     {
00049         c0 = (ch0 & ~0x80) >> 4 ;
00050         c1 = (ch1 & ~0x80) >> 4 ;
00051         s0 = ch0 & ~0xF0 ;
00052         s1 = ch1 & ~0xF0 ;
00053                 
00054         //ADC Count Value
00055         adc0 = int(16.5 * xpow(2,c0)) + (s0 * xpow(2,c0));
00056         adc1 = int(16.5 * xpow(2,c1)) + (s1 * xpow(2,c1));
00057         
00058         r = (double(adc1) / double(adc0));
00059         lux = double(adc0) * 0.46 * exp(-3.13 * r);
00060                 
00061         //give debug information
00062         //printf("\n\nZW: c0=%i s0=%i c1=%i s1=%i \n", c0, s0, c1, s1);
00063         //printf("ZW: adc0=%i, adc1=%i\n", adc0, adc1);
00064     }
00065     else
00066         printf("TSL2550: ***data not valid ! ***\n");    
00067 }
00068 
00069 void TSL2550::init() {
00070     unsigned short i;
00071     
00072     i = twi_read(TSL2550_ADDR, 0x03);
00073     if( i == 0x03 )
00074         printf("TSL2550: Init successful\n");
00075     else
00076         printf("TSL2550: Init ***failed*** !\n");    
00077 }
00078 
00079 unsigned short TSL2550::twi_read (unsigned short id, unsigned short data) {
00080     unsigned short i;
00081 
00082     //supply COMMAND byte to slave
00083     i2c.start();
00084     i2c.write(id);
00085     i2c.write(data);
00086 
00087     //demand ANSWER byte from slave    
00088     i2c.start();
00089     i2c.write(id | 1);
00090     i = i2c.read(0);
00091     i2c.stop();
00092     
00093 
00094     return i;
00095 }
00096 
00097 void TSL2550::twi_write (unsigned short id, unsigned short data) {
00098 
00099     i2c.start();
00100     i2c.write(id);
00101     i2c.write(data);
00102     i2c.stop();
00103 }
00104