Method 2: find time different by using interrupt

Figure 1: interrupt output

I find that it can be done by using interrupt in Arduino Uno. By using interrupt, it can find times tamp more accurately by utilize micros(). However, it has only 2 interrupt pin in Arduino Uno, to further development, it needs to be used Arduino Mega which has 6 interrupt pins. 

Sound generator

To produce a sound, I choose MSP-430 launchpad to generate audio sound.

Figure 1

In order to easily using code example , I use the integrated development environment called Energia. 

It is based on Arduino framework so it can be easily to understand in my project stage.

Time Different of arrival between different Sensor Output

Figure 1

The above figure shows that when the sound source near the mic2 instead of mic1, sound at mic2 will receive earlier than mic1 which is counted a smaller micro seconds.

In fact, each analogRead takes around 100 microseconds, which may make a significant error. However, the speed of sound is 343.2 metres per second (1,126 ft/s). The sound would travel only 0.1126 feet during an analogRead() in 100 microseconds.

To implement the circuit hence to receive enough signal, I use four microphone modules which shows in the following.

Figure 2

Figure 3

However, in figure 3, there are some error appointed. Mic4 always acquire signal at the first time although the sound source near mic2.

Sound Sensor Output

Figure 1: output of audio sensor

As the audio input is just a value, I try to implement this to another format in order to trigger the sound localization easily and more sensitive.

This program shown the loud sound or quiet on the serial monitor.

Figure 2: multiple output of audio sensor

As calculation of time different of arrival needs two time of arrival in two different sound sensors. I try to implement two sensor input in Arduino. Since I speak near mic1 instead of mic2, "LOUD,LOUD" message will display on mic1 first. Besides, since I speak near mic2 instead of mic1, "LOUD,LOUD" message will display on mic2 first.

sound module testing

Figure 1: sound module

I had bought sound module for sound acquisition. It need 3.3V to 5V and <10mA for working. It can adjust the sensitive by changing angle of bolt hole

Figure 2: output of sound module (no sound)

Figure 3: output of sound module (sound pulse)

Figure 4: output of sound module (no sound pulse)

Figure 5: output of sound module (sound pulse)

Figure 6: output value of sound module

Serial monitor with baud rate 9600 Hz
It can be detecting the sound by detecting voltage level at output pin in sound module

Sound module circuit prototype

Because of the limitation of sound card in computer, there will only two input audio channel input from microphone. That will difficult to accomplish sound localization in four individual audio input. Therefore, my supervisor suggest that use sound module for acquires audio input. Sound module is flexible for acquires more input channel instead of computer microphone.



Figure 1: Sound module

Based on the above figure, I was wiring the sound module for acquires audio input.

5 February 2016

 I use sony microphone which is given left and right channel stereo recording. It is important for my testing.


Figure 1: sony stereo microphone

Figure 2: Left channel microphone more closer to sound source

Figure 3: Right channel microphone more closer to sound source

19 January 2016

The main requirement of this project is to be implementing a reality application based on time difference of arrival. Create, develop and make use of the tool to enhance human convenience.  
Thus, it need to design a positioning system. 
In this system, it may include L
1. receiver module 
2. transmitter module
3. MCU or computer to do calculation

To find the position, it can need a shape signal pluse in different media, for example, sound, ultrasonic, light and radio.

The speed of sound: 343.2 m/s, Ultrasonic will transmit in 343.2 m/s.
The speed of light: 3 x 10⁸ m/s. Radio waves will travel at the speed of light
For speed different, I will choose sound to be media in order to reduce positioning error.


In this stage, I still to find hardware unit to receive signal pulse,
The first attract thing is to record the audio signal and transform to computer. It may use USB Microphone for further experiment.

12 January 2016

Thank for dr. martin chow, I had learnt the early positioning system based on TDOA technique such as Loran-C and OMEGA Navigation System. 

Loran-C is the radio navigation system for use on merchant ships. Generally, it seems to be a “Start” pulse when the master signal is revived. Then, it is a “Stop” signal when the secondary transmitter signal received. The time difference from “Start” to “Stop” is a constant. Based on the constant time difference value, it can plot a hyperbolic curve between signals from two stations. The position can be found by more hyperbolic.

OMEGA is the first radio navigation system in global-range and  need to use atomic clocks for synchronizing. Omega used to determine the transition time between transmitter and receiver. Then, it use hyperbolic geometry to find the target position.

29 December, 2015

The project may use mathematical derivation to analysis the procedure and result of positioning system based on TDOA technology. Thus, I have used the Matlab to simulate the procedure in 2D environment.

First, this matlab code is used to generate two random number form 0 to 200. Then, "sensor" coordinate will get those two random number for the x and y axis value respectively. Then, it will simulate TDOA system and calculate the output target coordinate after TDOA calculation.

Where "sensor" is the initial value generate before and "OUT" is the output value after TDOA calculation estimation. From the above result, TDOA system find the target in a very close range.
Later, I will generate the result value many times and compare them in order to get the error range.

6 October 2015

After the Seminar on Turnitin, I have learnt how to avoid running into plagiarism issues in my FYP written report.
And I recognized that I have to borrow some books for my FYP research.

I have borrowed a book called Ground- Based wireless positioning.
This book provides the techniques of wireless positioning, which include Time difference of arrival.
I have learnt the theory of positioning systems. I learnt the limitation and error of the positioning system based on TDOA. In this book, it gave the 3-dimension approach to calculate the corresponding position of the target.

29 September 2015

Principle of TDOA
In time different of arrival, at the beginning, all base stations are synchronized. 

There are three access points (AP1, AP2, AP3), when a client transmits a signal like a sound wave, each of access points will produce a time of arrival measurement. 

Equations of TDOA can be obtained.

In the above equations, AP1(x1,y1), AP2(x2,y2), AP3(x3,y3)

Each TDOA equation is a hyperbola, so the target location can be located as the intersection point of equations.    

11 September 2015

After a briefing session at 10 Step, Dr. Martin Chow has gave the general information about the final year project topic (Time Difference of Arrival )

Time Difference of Arrival (TDOA) is a measurement positioning system by determining time difference between base stations in order to find target location.