ELEC2645 (2015/16) / SRF02-JEB

Used command byte to return distance in inches.

Dependents:   2ndYearProject-DistanceSensor

Fork of SRF02 by Craig Evans

SRF02.cpp@2:45d62ec49ee9, 2016-03-27 (annotated)

Committer:
ll13j7b
Date:
Sun Mar 27 22:48:51 2016 +0000
Revision:
2:45d62ec49ee9
Parent:
0:b729d2ce03bd 
version 1.1

Who changed what in which revision?

UserRevisionLine numberNew contents of line
eencae 0:b729d2ce03bd 1 /**
eencae 0:b729d2ce03bd 2 @file SRF02.cpp
eencae 0:b729d2ce03bd 3
eencae 0:b729d2ce03bd 4 @brief Member functions implementations
eencae 0:b729d2ce03bd 5
eencae 0:b729d2ce03bd 6 */
eencae 0:b729d2ce03bd 7 #include "mbed.h"
eencae 0:b729d2ce03bd 8 #include "SRF02.h"
eencae 0:b729d2ce03bd 9
eencae 0:b729d2ce03bd 10 SRF02::SRF02(PinName sdaPin, PinName sclPin)
eencae 0:b729d2ce03bd 11 {
eencae 0:b729d2ce03bd 12 i2c = new I2C(sdaPin,sclPin); // create new I2C instance and initialise
eencae 0:b729d2ce03bd 13 i2c->frequency(400000); // I2C Fast Mode - 400kHz
eencae 0:b729d2ce03bd 14 leds = new BusOut(LED4,LED3,LED2,LED1);
eencae 0:b729d2ce03bd 15
eencae 0:b729d2ce03bd 16 }
eencae 0:b729d2ce03bd 17
eencae 0:b729d2ce03bd 18 int SRF02::getDistanceCm()
eencae 0:b729d2ce03bd 19 {
eencae 0:b729d2ce03bd 20 char data[2];
eencae 0:b729d2ce03bd 21
eencae 0:b729d2ce03bd 22 // need to send CM command to command register
eencae 0:b729d2ce03bd 23 data[0] = CMD_REG;
eencae 0:b729d2ce03bd 24 data[1] = CM_CMD;
eencae 0:b729d2ce03bd 25 int ack = i2c->write(SRF02_W_ADD,data,2);
eencae 0:b729d2ce03bd 26 if (ack)
eencae 0:b729d2ce03bd 27 error(); // if we don't receive acknowledgement, flash error message
eencae 0:b729d2ce03bd 28
eencae 0:b729d2ce03bd 29 // this will start the sensor ranging, the datasheet suggests a delay of at least 65 ms before reading the result
eencae 0:b729d2ce03bd 30 wait_ms(70);
eencae 0:b729d2ce03bd 31
eencae 0:b729d2ce03bd 32 // we can now read the result - tell the sensor we want the high byte
eencae 0:b729d2ce03bd 33 char reg = RANGE_H_REG;
eencae 0:b729d2ce03bd 34 ack = i2c->write(SRF02_W_ADD,&reg,1);
eencae 0:b729d2ce03bd 35 if (ack)
eencae 0:b729d2ce03bd 36 error(); // if we don't receive acknowledgement, flash error message
eencae 0:b729d2ce03bd 37
eencae 0:b729d2ce03bd 38 // if we read two bytes, the register is automatically incremented (H and L)
eencae 0:b729d2ce03bd 39 ack = i2c->read(SRF02_R_ADD,data,2);
eencae 0:b729d2ce03bd 40 if (ack)
eencae 0:b729d2ce03bd 41 error(); // if we don't receive acknowledgement, flash error message
eencae 0:b729d2ce03bd 42
eencae 0:b729d2ce03bd 43 // high byte is first, then low byte, so combine into 16-bit value
eencae 0:b729d2ce03bd 44 return (data[0] << 8) | data[1];
eencae 0:b729d2ce03bd 45 }
eencae 0:b729d2ce03bd 46
ll13j7b 2:45d62ec49ee9 47 int SRF02::getDistanceInch()
ll13j7b 2:45d62ec49ee9 48 {
ll13j7b 2:45d62ec49ee9 49 char data[2];
ll13j7b 2:45d62ec49ee9 50
ll13j7b 2:45d62ec49ee9 51 // need to send CM command to command register
ll13j7b 2:45d62ec49ee9 52 data[0] = CMD_REG;
ll13j7b 2:45d62ec49ee9 53 data[1] = INCH_CMD; // setting the new command byte to inches
ll13j7b 2:45d62ec49ee9 54 int ack = i2c->write(SRF02_W_ADD,data,2);
ll13j7b 2:45d62ec49ee9 55 if (ack)
ll13j7b 2:45d62ec49ee9 56 error(); // if we don't receive acknowledgement, flash error message
ll13j7b 2:45d62ec49ee9 57
ll13j7b 2:45d62ec49ee9 58 // this will start the sensor ranging, the datasheet suggests a delay of at least 65 ms before reading the result
ll13j7b 2:45d62ec49ee9 59 wait_ms(70);
ll13j7b 2:45d62ec49ee9 60
ll13j7b 2:45d62ec49ee9 61 // we can now read the result - tell the sensor we want the high byte
ll13j7b 2:45d62ec49ee9 62 char reg = RANGE_H_REG;
ll13j7b 2:45d62ec49ee9 63 ack = i2c->write(SRF02_W_ADD,&reg,1);
ll13j7b 2:45d62ec49ee9 64 if (ack)
ll13j7b 2:45d62ec49ee9 65 error(); // if we don't receive acknowledgement, flash error message
ll13j7b 2:45d62ec49ee9 66
ll13j7b 2:45d62ec49ee9 67 // if we read two bytes, the register is automatically incremented (H and L)
ll13j7b 2:45d62ec49ee9 68 ack = i2c->read(SRF02_R_ADD,data,2);
ll13j7b 2:45d62ec49ee9 69 if (ack)
ll13j7b 2:45d62ec49ee9 70 error(); // if we don't receive acknowledgement, flash error message
ll13j7b 2:45d62ec49ee9 71
ll13j7b 2:45d62ec49ee9 72 // high byte is first, then low byte, so combine into 16-bit value
ll13j7b 2:45d62ec49ee9 73 return (data[0] << 8) | data[1];
ll13j7b 2:45d62ec49ee9 74 }
ll13j7b 2:45d62ec49ee9 75
ll13j7b 2:45d62ec49ee9 76 void SRF02::error() // error message ( flashing LED )
eencae 0:b729d2ce03bd 77 {
eencae 0:b729d2ce03bd 78 while(1) {
eencae 0:b729d2ce03bd 79 leds->write(15);
eencae 0:b729d2ce03bd 80 wait(0.1);
eencae 0:b729d2ce03bd 81 leds->write(0);
eencae 0:b729d2ce03bd 82 wait(0.1);
eencae 0:b729d2ce03bd 83 }
eencae 0:b729d2ce03bd 84 }