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, char addr)
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     w_addr_ = addr; // set write address of sensor
00017     r_addr_ = w_addr_ + 1;  // read address has the lowest bit set (i.e. + 1)
00018 
00019 }
00020 
00021 int SRF02::getDistanceCm()
00022 {
00023     char data[2];
00024     
00025     // need to send CM command to command register
00026     data[0] = CMD_REG;
00027     data[1] = CM_CMD;
00028     int ack = i2c->write(w_addr_,data,2);  
00029     if (ack)
00030         error();  // if we don't receive acknowledgement, flash error message
00031         
00032     // this will start the sensor ranging, the datasheet suggests a delay of at least 65 ms before reading the result
00033     wait_ms(70);
00034     
00035     // we can now read the result - tell the sensor we want the high byte
00036     char reg = RANGE_H_REG;   
00037     ack = i2c->write(w_addr_,&reg,1);  
00038     if (ack)
00039         error();  // if we don't receive acknowledgement, flash error message
00040     
00041     // if we read two bytes, the register is automatically incremented (H and L)
00042     ack = i2c->read(r_addr_,data,2); 
00043     if (ack)
00044         error();  // if we don't receive acknowledgement, flash error message
00045 
00046     // high byte is first, then low byte, so combine into 16-bit value
00047     return (data[0] << 8) | data[1];
00048 }
00049 
00050 void SRF02::changeAddress(char addr) {
00051     
00052     char data[2];
00053     
00054     // sequence to change I2C (https://www.robot-electronics.co.uk/htm/srf02techI2C.htm)
00055     // need to write this sequence to the command register, followed by the new address
00056     
00057     data[0] = CMD_REG;
00058     data[1] = 0xA0;  // 1st byte in sequence
00059     int ack = i2c->write(w_addr_,data,2);  
00060     if (ack)
00061         error();  // if we don't receive acknowledgement, flash error message
00062         
00063     wait_ms(50);  // small delay in between 
00064     
00065     data[0] = CMD_REG;
00066     data[1] = 0xAA;   // 2nd byte in sequence
00067     ack = i2c->write(w_addr_,data,2);  
00068     if (ack)
00069         error();  // if we don't receive acknowledgement, flash error message
00070         
00071     wait_ms(50); // small delay in between 
00072     
00073     data[0] = CMD_REG;
00074     data[1] = 0xA5;  // 3rd byte in sequence
00075     ack = i2c->write(w_addr_,data,2);  
00076     if (ack)
00077         error();  // if we don't receive acknowledgement, flash error message
00078         
00079     wait_ms(50);  // small delay in between 
00080     
00081     data[0] = CMD_REG;  
00082     data[1] = addr;  // new address
00083     ack = i2c->write(w_addr_,data,2);  
00084     if (ack)
00085         error();  // if we don't receive acknowledgement, flash error message
00086     
00087     wait_ms(50);
00088     
00089 }
00090 
00091 void SRF02::error()
00092 {
00093     while(1) {
00094         leds->write(15);
00095         wait(0.1);
00096         leds->write(0);
00097         wait(0.1);    
00098     }    
00099 }