Using the SRF library to return a float value

Projects Programming
1

Hello, I've been experimenting with the SRF range finder library found here: http://arduino.cc/en/Tutorial/SFRRangerReader.

Here's the SRF code given at that link:

// I2C SRF10 or SRF08 Devantech Ultrasonic Ranger Finder 
// by Nicholas Zambetti <http://www.zambetti.com>
// and James Tichenor <http://www.jamestichenor.net> 

// Demonstrates use of the Wire library reading data from the 
// Devantech Utrasonic Rangers SFR08 and SFR10

// Created 29 April 2006

// This example code is in the public domain.


#include <Wire.h>

void setup()
{
  Wire.begin();                // join i2c bus (address optional for master)
  Serial.begin(9600);          // start serial communication at 9600bps
}

int reading = 0;

void loop()
{
  // step 1: instruct sensor to read echoes
  Wire.beginTransmission(112); // transmit to device #112 (0x70)
                               // the address specified in the datasheet is 224 (0xE0)
                               // but i2c adressing uses the high 7 bits so it's 112
  Wire.write(byte(0x00));      // sets register pointer to the command register (0x00)  
  Wire.write(byte(0x50));      // command sensor to measure in "inches" (0x50) 
                               // use 0x51 for centimeters
                               // use 0x52 for ping microseconds
  Wire.endTransmission();      // stop transmitting

  // step 2: wait for readings to happen
  delay(70);                   // datasheet suggests at least 65 milliseconds

  // step 3: instruct sensor to return a particular echo reading
  Wire.beginTransmission(112); // transmit to device #112
  Wire.write(byte(0x02));      // sets register pointer to echo #1 register (0x02)
  Wire.endTransmission();      // stop transmitting

  // step 4: request reading from sensor
  Wire.requestFrom(112, 2);    // request 2 bytes from slave device #112

  // step 5: receive reading from sensor
  if(2 <= Wire.available())    // if two bytes were received
  {
    reading = Wire.read();  // receive high byte (overwrites previous reading)
    reading = reading << 8;    // shift high byte to be high 8 bits
    reading |= Wire.read(); // receive low byte as lower 8 bits
    Serial.println(reading);   // print the reading
  }

  delay(250);                  // wait a bit since people have to read the output :)
}


/*

// The following code changes the address of a Devantech Ultrasonic Range Finder (SRF10 or SRF08)
// usage: changeAddress(0x70, 0xE6);

void changeAddress(byte oldAddress, byte newAddress)
{
  Wire.beginTransmission(oldAddress);
  Wire.write(byte(0x00));
  Wire.write(byte(0xA0));
  Wire.endTransmission();

  Wire.beginTransmission(oldAddress);
  Wire.write(byte(0x00));
  Wire.write(byte(0xAA));
  Wire.endTransmission();

  Wire.beginTransmission(oldAddress);
  Wire.write(byte(0x00));
  Wire.write(byte(0xA5));
  Wire.endTransmission();

  Wire.beginTransmission(oldAddress);
  Wire.write(byte(0x00));
  Wire.write(newAddress);
  Wire.endTransmission();
}

*/

The code is designed to return an integer value, which it does perfectly fine. However I need a more accurate reading than an integer value- at least two decimal places. How can I change the code to return a float value?

I try changing the declaration for "reading" from
int reading = 0; to float reading = 0.00;

but I get the following error:

SRF08.ino: In function 'void loop()':
SRF08:50: error: invalid operands of types 'float' and 'int' to binary 'operator<<'
SRF08:51: error: invalid operands of types 'float' and 'int' to binary 'operator|'
SRF08:51: error: in evaluation of 'operator|=(float, int)'

in step 5 of the code.

Thanks for any help!

2

The code is designed to return an integer value, which it does perfectly fine. However I need a more accurate reading than an integer value- at least two decimal places. How can I change the code to return a float value?

You are assuming that the sensor itself returns something other than an int. That is not borne out by the code you show. And, there is nothing on the link that suggests the value it can return is anything other than an int.

3

I was able to get it to work by measuring the echo time (in microseconds) and then doing some math to convert that number to inches.