This project features a collar intended for use with visually impaired canines. An ultrasonic sensor hangs below the collar and senses when an object is close and emits an audible beep warning the dog that they should proceed with caution. The overall design makes it so that the dog is not uncomfortable wearing the device (it hardly weighs anything at all) and it doesn't impede their movement.

Step 1: Parts

You will need:

An Arduino (I used an UNO) with i2c capabilities

A small speaker

Male header pins

PCB

NXT Sonar Sensor

NXT Wire connector

9v Battery

External Power for the Arduino (There are many options to use)

Dog Collar

Hot glue gun

Soldering Iron

Step 2: Hardware Assembly

The first thing we're going to do is breadboard everything to make sure it's all functioning properly. We'll get to making things permanent later on...

The first step is to strip one end of the NXT wire to expose the 6 colored wires. Connect them as follows or use the diagram provided.

White +9V

Black GND

Red GND

Green +5V

Yellow SCL and clockPin(12)

Blue SDA

Speaker GND and 13

Step 3: Software

The first step to getting the program to work is to open a new text document and paste the following:

#ifndef _I2CMASTER_H
#define _I2CMASTER_H   1
/************************************************************************* 
* Title:    C include file for the I2C master interface 
*           (i2cmaster.S or twimaster.c)
* Author:   Peter Fleury <pfleury@gmx.ch>  http://jump.to/fleury
* File:     $Id: i2cmaster.h,v 1.10 2005/03/06 22:39:57 Peter Exp $
* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
* Target:   any AVR device
* Usage:    see Doxygen manual
**************************************************************************/

#ifdef DOXYGEN
/**
 @defgroup pfleury_ic2master I2C Master library
 @code #include <i2cmaster.h> @endcode
  
 @brief I2C (TWI) Master Software Library
 Basic routines for communicating with I2C slave devices. This single master 
 implementation is limited to one bus master on the I2C bus. 
 This I2c library is implemented as a compact assembler software implementation of the I2C protocol 
 which runs on any AVR (i2cmaster.S) and as a TWI hardware interface for all AVR with built-in TWI hardware (twimaster.c).
 Since the API for these two implementations is exactly the same, an application can be linked either against the
 software I2C implementation or the hardware I2C implementation.
 Use 4.7k pull-up resistor on the SDA and SCL pin.
 
 Adapt the SCL and SDA port and pin definitions and eventually the delay routine in the module 
 i2cmaster.S to your target when using the software I2C implementation ! 
 
 Adjust the  CPU clock frequence F_CPU in twimaster.c or in the Makfile when using the TWI hardware implementaion.
 @note 
    The module i2cmaster.S is based on the Atmel Application Note AVR300, corrected and adapted 
    to GNU assembler and AVR-GCC C call interface.
    Replaced the incorrect quarter period delays found in AVR300 with 
    half period delays. 
    
 @author Peter Fleury pfleury@gmx.ch  http://jump.to/fleury
 @par API Usage Example
  The following code shows typical usage of this library, see example test_i2cmaster.c
 @code
 #include <i2cmaster.h>
 #define Dev24C02  0xA2      // device address of EEPROM 24C02, see datasheet
 int main(void)
 {
     unsigned char ret;
     i2c_init();                             // initialize I2C library
     // write 0x75 to EEPROM address 5 (Byte Write) 
     i2c_start_wait(Dev24C02+I2C_WRITE);     // set device address and write mode
     i2c_write(0x05);                        // write address = 5
     i2c_write(0x75);                        // write value 0x75 to EEPROM
     i2c_stop();                             // set stop conditon = release bus
     // read previously written value back from EEPROM address 5 
     i2c_start_wait(Dev24C02+I2C_WRITE);     // set device address and write mode
     i2c_write(0x05);                        // write address = 5
     i2c_rep_start(Dev24C02+I2C_READ);       // set device address and read mode
     ret = i2c_readNak();                    // read one byte from EEPROM
     i2c_stop();
     for(;;);
 }
 @endcode
*/
#endif /* DOXYGEN */

/**@{*/

#if (__GNUC__ * 100 + __GNUC_MINOR__) < 304
#error "This library requires AVR-GCC 3.4 or later, update to newer AVR-GCC compiler !"
#endif

#include <avr/io.h>

/** defines the data direction (reading from I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_READ    1

/** defines the data direction (writing to I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_WRITE   0


/**
 @brief initialize the I2C master interace. Need to be called only once 
 @param  void
 @return none
 */
extern void i2c_init(void);


/** 
 @brief Terminates the data transfer and releases the I2C bus 
 @param void
 @return none
 */
extern void i2c_stop(void);


/** 
 @brief Issues a start condition and sends address and transfer direction 
  
 @param    addr address and transfer direction of I2C device
 @retval   0   device accessible 
 @retval   1   failed to access device 
 */
extern unsigned char i2c_start(unsigned char addr);


/**
 @brief Issues a repeated start condition and sends address and transfer direction 
 @param   addr address and transfer direction of I2C device
 @retval  0 device accessible
 @retval  1 failed to access device
 */
extern unsigned char i2c_rep_start(unsigned char addr);


/**
 @brief Issues a start condition and sends address and transfer direction 
   
 If device is busy, use ack polling to wait until device ready 
 @param    addr address and transfer direction of I2C device
 @return   none
 */
extern void i2c_start_wait(unsigned char addr);

 
/**
 @brief Send one byte to I2C device
 @param    data  byte to be transfered
 @retval   0 write successful
 @retval   1 write failed
 */
extern unsigned char i2c_write(unsigned char data);


/**
 @brief    read one byte from the I2C device, request more data from device 
 @return   byte read from I2C device
 */
extern unsigned char i2c_readAck(void);

/**
 @brief    read one byte from the I2C device, read is followed by a stop condition 
 @return   byte read from I2C device
 */
extern unsigned char i2c_readNak(void);

/** 
 @brief    read one byte from the I2C device
 
 Implemented as a macro, which calls either i2c_readAck or i2c_readNak
 
 @param    ack 1 send ack, request more data from device<br>
               0 send nak, read is followed by a stop condition 
 @return   byte read from I2C device
 */
extern unsigned char i2c_read(unsigned char ack);
#define i2c_read(ack)  (ack) ? i2c_readAck() : i2c_readNak(); 


/**@}*/
#endif

Save the file as i2cmaster.h

Next open up the Arduino software and create a new program with the following code:

#include <i2cmaster.h>

byte clockPin = 12;
byte buf[9];//Buffer to store the received valeus
byte addr = 0x02;//address 0x02 in a 8-bit context - 0x01 in a 7-bit context
byte distance;</p><p>void setup()
{  
  i2c_init();//I2C frequency = 11494,253Hz
  Serial.begin(9600);
  printUltrasonicCommand(0x00);//Read Version
  printUltrasonicCommand(0x08);//Read Product ID
  printUltrasonicCommand(0x10);//Read Sensor Type
  printUltrasonicCommand(0x14);//Read Measurement Units 
  pinMode(13,OUTPUT);
}
  </p><p>void loop()
{    
  //printUltrasonicCommand(0x42);//Read Measurement Byte 0
  
  distance = readDistance();
  if(distance == 0xFF)
    Serial.println("Error Reading Distance");
  else
    Serial.println(distance, DEC);
  if(distance<30){
    tone(13,4000);
    delay(200);
    noTone(13);
  }
}
byte readDistance()
{  
  delay(100);//There has to be a delay between commands
  byte cmd = 0x42;//Read Measurement Byte 0
    
  pinMode(clockPin, INPUT);//Needed for writing to work
  digitalWrite(clockPin, HIGH);  
  
  if(i2c_start(addr+I2C_WRITE))//Check if there is an error
  {
    Serial.println("ERROR i2c_start");
    i2c_stop();
    return 0xFF;
  }    
  if(i2c_write(cmd))//Check if there is an error
  {
    Serial.println("ERROR i2c_write");
    i2c_stop();
    return 0xFF;
  }  
  i2c_stop();
    
  delayMicroseconds(60);//Needed for receiving to work
  pinMode(clockPin, OUTPUT);
  digitalWrite(clockPin, LOW); 
  delayMicroseconds(34);
  pinMode(clockPin, INPUT);
  digitalWrite(clockPin, HIGH); 
  delayMicroseconds(60);  
   
  if(i2c_rep_start(addr+I2C_READ))//Check if there is an error
  {
    Serial.println("ERROR i2c_rep_start");
    i2c_stop();    
    return 0xFF;
  }  
  for(int i = 0; i < 8; i++)
    buf[i] = i2c_readAck();
  buf[8] = i2c_readNak();  
  i2c_stop(); 
  
  return buf[0];   
}
void printUltrasonicCommand(byte cmd)
{
  delay(100);//There has to be a delay between commands
    
  pinMode(clockPin, INPUT);//Needed for writing to work
  digitalWrite(clockPin, HIGH);
  
  if(i2c_start(addr+I2C_WRITE))//Check if there is an error
  {
    Serial.println("ERROR i2c_start");
    i2c_stop();
    return;
  }
  if(i2c_write(cmd))//Check if there is an error
  {
    Serial.println("ERROR i2c_write");
    i2c_stop();
    return;
  }
  i2c_stop();
    
  delayMicroseconds(60);//Needed for receiving to work
  pinMode(clockPin, OUTPUT);
  digitalWrite(clockPin, LOW); 
  delayMicroseconds(34);
  pinMode(clockPin, INPUT);
  digitalWrite(clockPin, HIGH); 
  delayMicroseconds(60);  </p><p>  if(i2c_rep_start(addr+I2C_READ))//Check if there is an error
  {
    Serial.println("ERROR i2c_rep_start");
    i2c_stop();
    return;
  }
  for(int i = 0; i < 8; i++)
    buf[i] = i2c_readAck();
  buf[8] = i2c_readNak();
  i2c_stop();  
  
  if(cmd == 0x00 || cmd == 0x08 || cmd == 0x10 || cmd == 0x14)
  {
      for(int i = 0; i < 9; i++)
      {
        if(buf[i] != 0xFF && buf[i] != 0x00)
          Serial.print(buf[i]);
        else
          break;
      }              
  }
  else
    Serial.print(buf[0], DEC);  </p><p>  Serial.println("");      
}
/*
' Wires on NXT jack plug.
' Wire colours may vary. Pin 1 is always end nearest latch.
' 1 White +9V
' 2 Black GND
' 3 Red GND
' 4 Green +5V
' 5 Yellow SCL - also connect clockpin to give a extra low impuls
' 6 Blue SDA
' Do not use i2c pullup resistor - already provided within sensor.
*/</p>

Verify and Compile the code onto your Arduino. If you get an error make sure that the i2cmaster.h file is accessible by the Arduino code.

You can adjust the distance from which the beeping will occur by lowering or raising the value in the if(distance<30) condition.

Step 4: The PCB

Now is the time where you've tested everything and it's time to put it into a more permanent state. Start by soldering the male header pins in a way that the PCB can easily clip onto the Arduino. Take your time soldering in the connections making sure that you don't create any short circuits. After you have soldered the main connections together cover the more flimsy connections to the wires with hot glue. After this, hot glue the speaker to the top and solder those wires into place. Refer to the pictures for a better understanding of what is should roughly look like.

Step 5: Mounting the Sensor

Before proceeding have a look at the collar and decide the best way to attach the sensor for the height and comfort-ability of your dog. I ended up hot-gluing the sensor so that gravity would always keep the sensor pointed forward no matter what.

When you've mounted the sensor, attach the rest of the system to the collar making sure to leave room for the dog's head to be inserted and removed from the collar.

At this point, you should have a fully functional sonar collar for your dog and after hooking up the external power supply so that free movement is able, you're ready to go!