SRF02.cpp

00001 /**
00002 @file SRF02.cpp
00003  
00004 @brief Member functions implementations
00005  
00006 */
00007 #include "mbed.h"
00008 #include "SRF02.h"
00009  
00010 SRF02::SRF02(PinName sdaPin, PinName sclPin)
00011 {
00012     i2c = new I2C(sdaPin,sclPin); // create new I2C instance and initialise
00013     i2c->frequency(400000);       // I2C Fast Mode - 400kHz
00014     leds = new BusOut(LED4,LED3,LED2,LED1);
00015  
00016 }
00017  
00018 int SRF02::getDistanceCm()
00019 {
00020     char data[2];
00021     
00022     // need to send CM command to command register
00023     data[0] = CMD_REG;
00024     data[1] = CM_CMD;
00025     int ack = i2c->write(SRF02_W_ADD,data,2);  
00026     if (ack)
00027         error();  // if we don't receive acknowledgement, flash error message
00028         
00029     // this will start the sensor ranging, the datasheet suggests a delay of at least 65 ms before reading the result
00030     wait_ms(70);
00031     
00032     // we can now read the result - tell the sensor we want the high byte
00033     char reg = RANGE_H_REG;   
00034     ack = i2c->write(SRF02_W_ADD,&reg,1);  
00035     if (ack)
00036         error();  // if we don't receive acknowledgement, flash error message
00037     
00038     // if we read two bytes, the register is automatically incremented (H and L)
00039     ack = i2c->read(SRF02_R_ADD,data,2); 
00040     if (ack)
00041         error();  // if we don't receive acknowledgement, flash error message
00042  
00043     // high byte is first, then low byte, so combine into 16-bit value
00044     return (data[0] << 8) | data[1];
00045 }
00046  
00047 void SRF02::error()
00048 {
00049     while(1) {
00050         leds->write(15);
00051         wait(0.1);
00052         leds->write(0);
00053         wait(0.1);    
00054     }    
00055 }