Decoding Codec Of Amplitude Shift Key Computer Science Essay

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This project concentrates on coding and decoding of Amplitude Shift Key for wireless transmission at frequency 40.68MHz.

This project is designed and constructed as a pager. The main function of these devices is to send message at the transmitter and receive the text messages at the receiver side. It is very much like communicating with a Beep-Pager.

This project uses the microcontroller (PIC 16F877A) to control sending of data. For transmission, the microcontroller switch the output of the RF 40.68MHz signal generator to create an ASK signal. At the receiver side, the RF signal passes thru the LNA and PA to reach an envelope detector to get the analogue version of data signal. A decision circuit is use to convert the analogue to digital signal.

Coding and decoding process will be fully control by the microcontroller using asynchronous transmission operation whereby both transmitter and receiver use separate clocks which are of similar frequency by agreeing a nominal transmission rate of 200 bps. The character of the message is send using ASCII code. When detected the start bit, the microcontroller need to delay 7ms to jump over the start bit and get to the centre point of the first bit of the ASCII code. The delay for the receiving the other bits of ASCII code is 5ms, same as the data bit period/duration hence try to maintain centre point detection in other bits.

1.2 Project Aim

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The purpose of this project is to design a method to code and decode the digital data for asynchronous transmission at 40.68MHz with Amplitude Shift Keying.

1.3 Technical Objectives

No

Technical Objectives

1

To acquire digital data input from keypad using microcontroller

2

Encode the digital data using ASK for wireless transmission

3

Detect ASK signal at the receiver

4

Create a suitable method for symbol timing recovery

5

To read the digital data correctly at receiver

6

Display the data on LCD

Table 1: List of Technical Objectives

1.4 Limitations

Due to the PIC limitation, the data rate is low

(Maximum 200 bps)

No error checking due to one way communication.

Keypad can only key in lowercase alphabet

Maximum message size is limit to 40 characters

Chapter 2: Literature Review

2.1 Synchronous & Asynchronous Data Transmission

Term synchronous is used to describe a continuous and consistent timed transfer of data blocks. There is large amount of data is transmitting in very fast from one location to another in this type of connection. The speed of the synchronous connection is attained by transferring data in large blocks instead of individual characters. [1]

The term asynchronous is used to describe the process where transmitted data with specifying the beginning and end of each character with a start and stop bit. In asynchronous transmission, the data transfer which signals are sent in spurts and spaced by varying time intervals. This arrangement is in contrast to synchronous transmission where data is sent in continuous blocks of characters (called frame or packets). Spaced by fixing time intervals, asynchronous transmission is used commonly for communications over telephone lines, whereas most network protocols (such as Ethernet, SONET, token ring) use synchronous transmission. [2]

For synchronous transmission, no start and stop bits are used but instead synchronize transmission occur using the same clock signal at both the receiving and sending component. A continual stream of data is then sent between the two nodes. Due to there being no start and stop bits the data transfer rate is quicker. [3]

2.2 Amplitude Shift Key

Amplitude shift keying (ASK) in the context of digital communications is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels. These are related to the number of levels adopted by the digital message.

For a binary message sequence there are two levels, one of which is typically zero. Thus the modulated waveform consists of bursts of a sinusoid.

Figure 1 illustrates a binary ASK signal (lower), together with the binary sequence which initiated it (upper). Neither signal has been band limited.

Figure 1: ASK signal and the message

There are sharp discontinuities shown at the transition points. These result in the signal having an unnecessarily wide bandwidth. Band limiting is generally introduced before transmission, in which case these discontinuities would be 'rounded off'. The band limiting may be applied to the digital message, or the modulated signal itself. The data rate is often made a sub-multiple of the carrier frequency. This has been done in the waveform of Figure 1. [4]

2.3 Parity bit

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Parity bit is a simplest form of error detecting code. There are two variants of parity bits that are EVEN PARITY and ODD PARITY. For EVEN PARITY, the parity bit is set to '1' when the number of '1' in the character is odd (not include the parity bit). This is to make the entire stream of bits of '1' become even. Similar to ODD PARITY, when the number of '1' in the character is even (not include the parity bit), the parity bit will set to '1' to let the bit stream of '1' become in odd number.

2.4 Envelope Detector

Envelope detector is a device use to demodulate ASK signals to original data.. Any ASK signal can be written in the following form [5]

x(t) = R(t)cos(ωt+φ(t)) when data is high (1)

and x(t) = 0 when data is low (0)

2.4.1 Diode Detector

The simplest form of envelope detector is the diode detector. A diode detector is just simply connected a diode between the input and output of a circuit and also connect a resistor and capacitor in parallel to the ground from the output of the circuit. If the resistor and capacitor are correctly chosen, the output of this circuit should approximate a voltage-shifted version of the original signal. [5]

2.4.2 Precision detector

An envelope detector can also be constructed to use a precision rectifier feeding into a low-pass filter. [5]

2.4.3 Drawbacks

The envelope detector has several drawbacks

The input to the detector must be band-pass filtered around the desired signal, or else the detector will simultaneously demodulate several signals. The filtering can be done with a tunable filter or, more practically, a super heterodyne receiver

It is more susceptible to noise than a product detector

If the signal is over modulated, distortion will occur

Most of these drawbacks are relatively minor and are usually acceptable tradeoffs for the simplicity and low-cost of using an envelope detector. [5]

2.5 ASCII

ASCII (American Standard Code for Information Interchange) is the standard code used for information interchange and communication between data processing systems, including Internet. ASCII initially contained 128 7-bit coded character including alphabetic, numeric, graphic and control characters. It has been extended to include system or country specific characters. ASCII is the U.S. version of International Reference Alphabet (IRA) No.5 (formerly known as International Alphabet No.5, or "IA5") as specified in ITU-T Recommendation T.50. [6]

ASCII Table

Table 2: ASCII Table [6]

Chapter 3: Background Information (Methodology)

3.1 Block Diagram

3.1.1 Block Diagram for Transmitter

Signal generator set at 40.68MHz

Microcontroller (PIC16F877A)

4 x 20 LCD

Keypad

1

. , ? !

2

a b c

3

d e f

A

4

g h i

5

j k l

6

m n o

B

7

p q r s

8

t u v

9

w x y z

C

CLEAR

*

* / + -

0

space

#

# : ; ( )

D

SEND

Antenna

3.1.1.1 Block Diagram explanation

For the transmitter side, users key-in the message using keypad with key map which is similar to hand phone keypad. After complete message, press button 'D' to send out the message. Message will first be code in PIC to ASCII format and send via in serial to control output switching of signal generator set at 40.68MHz. The ASK signal is then broadcast thru antenna.

3.1.2 Block Diagram for Receiver

Microcontroller (PIC16F877A)

4 x 20 LCD

Antenna

Envelope Detector

Decision Circuit

LNA

PA

PA

3.1.2.1 Block Diagram explanation

At the receiver side, the ASK signal from the antenna is passing thru the amplifier to amplify the weak signal to stronger signal for processing. After amplifier, the ASK signals go in envelope detector and output an analog version of the data. The analog version of the data signal passes thru a decision circuit to become digital signal. After that, the microcontroller will receive the signal and decoding the data and display it on LCD. (The part in yellow box is not include in this project)

3.2 Hardware Description

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This project consists of 3 circuit board (in PCB) which is Transmitter Board (include PIC, LCD & Keypad), Receiver Board (PIC & LCD) and the last board is combine Envelop Detector circuit and decision circuit together.

In transmitter board, the keypad is use to let user enter the message. The LCD is to interface with user to let user see what they key-in for the message and send out. For the microcontroller, is use to control the input and output process for overall system of transmitter. Microcontroller gets the input from the user and display on the LCD and send out the data to signal generator to generate ASK signal. Code and decode process is done by microcontroller.

Before go in to receiver board, the RF signal will pass thru the envelope detector (low pass filter) to get the analog version of original data. After get the output from the envelope detector, the signals go thru the decision circuit to get stable digital signal for PIC to further processing.

The PIC will receive the digital data and decode the bit stream to the original character that been send. The program will wait until received the terminated character "T" for telling the system this is the end for this transmission. After system receives the termination character then the message or character will be display on the LCD.

3.2.1 PIC 16F877A

Figure 2: PIC16F877A pin layout [18]

Above is the pin layout for PIC 16F877A. This PIC is chosen because this is PIC is one of the most popular PIC microcontroller and easy to found. It is a single integrated containing process core, memory, programmable input/output peripherals. PIC is made by Microchip Technology as a family of Harvard architecture microcontrollers. PIC was first known as "Programmable Interface Controller" and now it's known as "Programmable Intelligent Computer". [7]

With its advance technology, PIC can control this project with sending and receive of digital communication process and code and decode process. Furthermore, with the lower cost and smaller size of PIC leads it to be the best option. There are various types of PIC and PIC16F877A was chosen. 16F means that it's 16 series Flash memory PIC.

Figure 3: PIC16F87XA Device Features [18]

For this project, PIC16F877A is controlling the digital data transmission and process. This PIC consists of 33 I/O pins but for this project, not all of the pins are used. The pin configuration is as shown below:

3.2.1.1 Transmitter PIC PORT configuration

Port A: LCD

RA0-RA3 = LCD Data pins

RA4 = LCD RS pin

RA5 = LCD Enable pin

Port B: Keypad

RB0 - RB3 = Keypad column pins

RB4-RB7 = Keypad row pins

Port D: Data Transmission

RD0 = Data bit Output to Signal Generator

3.2.1.2 Receiver PIC PORT configuration

Port A: LCD

RA0-RA3 = LCD Data pins

RA4 = LCD RS pin

RA5 = LCD Enable pin

Port C: Data Transmission

RC7 = Data pin receive data from decision circuit

Port D: Data Transmission

RD0 = Data pin output data bit to Signal Generator

3.2.3 LCD (20x4)

D:\My Documents\Inti\Diploma\Tan Perh Hoong Jan 09 (Wireless Information Display System)\Diploma Project\JAN 2009\Tan Perh Hoong\Pictures\Components\LCD Front.jpg

Figure 4: 20x4 LCD

LCD is known as Liquid Crystal Display which is a flat and thin electronic visual display where it uses light modulating properties of liquid crystals which this crystal doesn't emit light directly. [8]

LCD is chosen due to size choices, lighter weight, more compact, portable and less expensive. For this system, 20x4 LCD was used because the character per line is more and the lines available is more compare to 16x2 LCD.

LCD 20x4 has 8 data pins where it can support 4 or 8 bits like the 16x2 LCD. In this project, 4 bit data is used therefore only 4 data pins is needed. LCD pin is connected to PIC16F877A port A. LCD is programmed using MPLAB software where this program supplies a driver for basic LCD module. LCD pins are connected as:

Pin Number

Symbol

Function

1

Vss

GND

2

Vdd

3V to 5V

3

Vo

Contrast Adjustment

4

RS

H/L Register Select Signal

5

R/ W

H/L Read/Write Signal

6

E

H → L Enable Signal

7

DB0

H/L Data Bus Line

8

DB1

H/L Data Bus Line

9

DB2

H/L Data Bus Line

10

DB3

H/L Data Bus Line

11

DB4

H/L Data Bus Line

12

DB5

H/L Data Bus Line

13

DB6

H/L Data Bus Line

14

DB7

H/L Data Bus Line

15

A/Vee

4.2V for LED/Negative Voltage Output

16

K

Power Supply for B/L (0V)

Table 3: LCD Pins Table

The LCD is used to display for the user for seeing what the message or character they type or received.

3.2.3 4x4 Keypad

Keypad

Figure 5: 4x4 Keypad

Figure 6: Keypad Configuration

Keypad

1

. , ? !

2

a b c

3

d e f

A

4

g h i

5

j k l

6

m n o

B

7

p q r s

8

t u v

9

w x y z

C

CLEAR

*

* / + -

0

space

#

# : ; ( )

D

SEND

Figure 7: Keypad key map

Keypad is a set of buttons arranged in a block that bear digits, symbol and sometimes a complete set of alphabetical letters. Keypad is used as an input device to the system that needs to enter information or interface with user. For this project, 4x4 keypad is used. [9]

Based on Figure 7, the alphabetic is used to choose which menu that was written in PIC. While for the numeric pad, it is used to input the message to the PIC and send out. The first 3 column is the alphanumeric and symbol input and the last column is use for command.

Keypad pin is connected to PIC's port B0 till B7.

Pin No

Pin 1 (RB0)

Pin 2 (RB1)

Pin 3 (RB2)

Pin 4 (RB3)

Pin 5 (RB4)

Pin 6 (RB5)

Pin 7 (RB6)

Pin 8 (RB7)

Location

C1

C2

C3

C4

R1

R2

R3

R4

Table 4: Keypad Pin Allocation

3.2.4 Amplifier (LM 10)

Figure 8: LM10 Pin Layout [10]

The op-amp LM10 using in this project in decision circuit. This decision circuit is to convert the analog signal to the stable digital signal. The op-amp act as comparator in this project. The actual connection will be shown in the schematic that will discuss later in hardware schematic. The LM10 is chosen (rather than LM741) because it has low output voltage close to 0V (for low).

The LM10 series are monolithic linear ICs consisting of a precision reference, an adjustable reference buffer and an independent, high quality op amp. The unit can operate from a total supply voltage as low as 1.1V or as high as 40V, drawing only 270µA. A complementary output stage swings within 15 mV of the supply terminals or will deliver ±20 mA output current with ±0.4V saturation. Reference output can be as low as 200 mV. [11]

3.2.5 Schematic Diagram for Hardware

3.2.5.1 Transmitter Schematic Diagram

Figure 9: Transmitter schematic diagram

3.2.5.1.1 Transmitter Schematic Diagram explanation

For PIC16F877A, 4 MHz crystal is used and connected at pin 13 and 14 with 2 22pF capacitor. Crystal needs loading capacitors to work at the exact operating frequency. At pin 1, that's the master clear pin that is active low. So it is connected to 5V supply. This pin is to reset the PIC.

LM7805 is use to supply the constant 5V supply to the circuit.

Port A is connected to LCD which refers the data pin table provided in LCD data sheet. Port B is connected to keypad. The resister use for keypad is 1kΩ for column, 10kΩ for row. The pin that's no used in this project is grounded for not affecting the data pin that's transmitting data. The output data pin is to output data to signal generator.

3.2.5.2 Receiver Schematic Diagram

Figure 10: Receiver schematic diagram

3.2.5.2.1 Receiver schematic diagram explanation

For PIC16F877A, 4 MHz crystal is used and connected at pin 13 and 14 with 2 22pF capacitor. Crystal needs loading capacitors to work at the exact operating frequency. At pin 1, that's the master clear pin that is active low. So it is connected to 5V supply. This pin is to reset the PIC.

LM7805 is use to supply the constant 5V supply to the circuit.

Port A is connected to LCD which refers the data pin table provided in LCD data sheet. The pin that's no used in this project is grounded for not affecting the data pin that's receiving data. The input data pin is to get data from decision circuit.

3.2.5.3 Envelope Detector & Decision circuit schematic diagram

Figure 11: Envelope Detector & Decision Circuit schematic diagram

3.2.5.3.1 Envelope Detector & Decision circuit schematic diagram explanation

Envelope detector is consists of three components. The diode is to filter out the negative side of waveform. The best choice of the diode is the germanium diode but it hard to get in market so the normal diode is choose to replace it. The resister and capacitor is playing an important role in the envelope detector. The value of the resister must be calculated correctly to get the correct envelope. Below is some calculation for the RC value.

fc = carrier frequency

R = resistor value

C = capacitor value

w = 2Ï€f

C = 100pF (work well for frequency under 100 MHz)

R = 330kΩ

RC = 33u

The RC value is fulfilling the equation condition.

The LM10 is chosen (rather than LM741) because it has low output voltage close to 0V (for low) for the decision circuit, while LM741 output voltage greater than 1 volt for low.

Chapter 4: Background information for Software (Methodology)

4.1 C Programming Language

C language is a general-purpose computer programming language designed for implementing system software (operating system or utility system) and widely used for developing application software (graphic software or media players). C is an imperative (procedural) systems implementation language.

It was designed to be compiled using a relatively straightforward compiler, to provide low-level access to memory, to provide language constructs that map efficiently to machine instructions, and to require minimal run-time support. C was therefore useful for many applications that had formerly been coded in assembly language. [12]

For this project, MPLAB is used for writing the program in the C programming. In C language is allow to written the program in object-oriented. This object-oriented mean the data not only define the data type of a data structure, but also the types of operations (functions) that can be applied to the data structure. In this way, the data structure becomes an object that includes both data and functions. In addition, programmers can create relationships between one object and another. For example, objects can inherit characteristics from other objects. Thus the object can be passing to another function to process. [13] In this project, object-oriented programming is used to passing the message to one and another function for do the processing. Example in this project, the message that user enter is pass to a function to send the message with send out the message with stream of bit rather than a whole character.

In this project, some references are taken from the Hi-tech C sample program that is provided in the sample program. That's also can be downloaded at the hi-tech website with simple sample C program.

4.2 Flowchart

4.2.1 Flowchart of transmitter

Yes

No

Yes

No

Clear a character

'Clear' pressed?

'Send' pressed?

Detect key pressed

Display character on LCD

Start

Send out the message

(Function)

Initialization

4.2.1.1 Flowchart of transmitter explanation

At the beginning, when the power supply is ON, the program will setup the LCD and setting up interrupt setting for keypad. After setting up LCD and keypad, the input and output port also set to the starting of the program. This all is done in the Initialization before the program is starting to run in main program.

When the program is start running in main loop, the program is detect for the user input. The priority of the button press is "CLEAR", follows by "SEND" and last is the alphanumeric and symbol input. If the "CLEAR" button is pressed, one character will be deleted each time. If the button "SEND" is pressed, the message that been enter by user will send to function 'send message' to send out the message. This function will be discuss in the following flowchart.

For the alphanumeric input can refer the key map in Figure 7. For the alphanumeric input, one button can be representing more than 1 character or symbol. The key map is design base on the hand phone keypad for more user friendly since now people is more familiar with the input key map of hand phone. When the user is keep on pressing the same button as shown in Figure 7, the input will change accordingly with the display on the LCD. The time gap for the user to change the alphanumeric or symbol is set to one second. After one key is pressed, the program will go back to detect for the new key input pressed in main loop.

4.2.2 Flowchart of Sending Function

Yes

No

No

Yes

Start

Send start bit (Low)

Send next bit

Send stop bit (High)

Last character?

Display "Send Success"

End

8 bits send?

Delay

Delay

Delay

Send 'T' for termination

4.2.2.1 Flowchart of Sending Function explanation

When the message is passing into this function, the program will send the character out with ASCII code. One character is understood as a 8 bits data. The program will send out a start bit that is set as 'low' and continue by the 8 bit data, bit by bit. To send the data bit by bit, shifting method is used. After the 8 bits data is send, a stop that is 'high', is send to let the receiver know that this character is finish sending. The process is repeated until all the character is been finish send. When program is detecting the last character, the termination character is send out to inform the receiver that the whole message is delivered. The LCD will display the info when the message is finish delivered.

4.2.3 Flowchart of Receiver

Yes

No

Yes

No

Yes

No

Start bit received?

Display all character on LCD

start

Initialization

Receive bit

8 bits Received?

Delay

Delay

Character "T" received?

Clear LCD

4.2.3.1 Flowchart of Receiver explanation

At the beginning, when the power supply is ON, the program will setup the LCD and the input and output port at Initialization. After everything is setting up, the program will go into the main loop.

In main loop, the program is keep on checking that is there is a start bit received? If the start bit is received then the program will start to receive 1bit 8 times for a character. After received the character the program will check is that character is termination character or not. If the character is the termination character then program will display message or character it received at the LCD. If not termination character, program will keep on waiting for the next start bit to receive the next character.

The delay function is used in the program is to get the centre point detection of the data bit. For this system, each bit is 5ms period. When detected the start bit, the program need to delay 7ms to jump over the start bit and get to the centre point of the first bit of the ASCII code. The delay for the receiving the other bits of ASCII code is 5ms, same as the data bit period/duration hence try to maintain centre point detection in the other 8 bits.

Chapter 5: Results and Discussion

5.1 Transmitter

C:\Documents and Settings\User\Desktop\FYP\fyp photo\IMG_9157.JPG

Figure 12: Test result for transmitting message

For the transmitter, the keypad can be input the character correctly with expected result. The Figure 12 above shown that the message "hello" (at row 3) is enter with the keypad and can display correctly in the LCD.

C:\Documents and Settings\User\Desktop\FYP\fyp photo\NewFile_02.bmp

Figure 13: Testing result for Transmitter

C:\Documents and Settings\User\Desktop\FYP\fyp photo\IMG_9159.JPG

Figure 14: Signal Generator

The transmitter is been tested by sending known pulse to signal generator to produce ASK signal. In Figure 13 shown that the result for the output from PIC and the output from signal generator (Figure 14) to antenna. In Figure 13, the channel 1 (yellow) is the digital signal from the PIC. Channel 2 (green) is the ASK signal generate from signal generator when controlled with the digital signal from PIC. The reason testing with knowing data pulse is to make it easy for observation. With known data pulse, is much easier to do troubleshooting.

5.2 Envelop Detector

C:\Documents and Settings\User\Desktop\FYP\fyp photo\After_diod.bmp

Figure 15: Test result for Envelope Detector

The Figure 15 above is the tested result for the envelope detector for the known data pulse. The channel 1 (yellow) is the ASK signal that received. Channel 2 (green) is the signal after pass thru the envelope detector. From the result, can observe that after passing the envelope detector, the negative side is been filter out and the signal is getting back to the original data that been sent by transmitter side.

5.3 Decision Circuit

C:\Documents and Settings\User\Desktop\FYP\fyp photo\Final_resu.bmp

Figure 16: Test result for Decision Circuit

Figure 16 is the tested result for the decision circuit. The channel 1(yellow) is the analog waveform from envelope detector. The channel 2 (green) is the result output from the decision circuit. The decision circuit is to change the analog signal to stable digital signal for PIC to do further process. From the result, it can be observed that the digital data state is discrete either 5V or 0V.

5.4 Receiver

C:\Documents and Settings\User\Desktop\FYP\fyp photo\IMG_9158.JPG

Figure 17: Test result for receiving message

At the receiver side, the signal is getting from decision circuit and then only passes into PIC. From the Figure 17 above, the signal sending by the transmitter is received correctly at receiver and display at LCD. It's proven that the signal is received and decoding correctly at the receiver side.

5.5 Discussion

At the transmitter and receiver side the main task is to code and decode the message in to bit stream. The purpose of convert the character into the stream of bit is because in transmitter, the data is transmit in serial but not parallel. So, to send data thru transmitter, the data must be in serial.

For ensure the receiver can receive the message correctly, the start bit and stop bit is been added to the beginning and the end of each character. The start bit (low) is to let the receiver side know when the data is starting send. The stop bit at the end of character is to set back the bit to an ideal (high) or not the receiver may have the possibility to read the last bit of data as the new start bit, then the result received will be incorrect.

For the envelope detector, there were involved three components. The diode is to filter the negative side signal. The capacitor and resistor is a low pass filter that detects the low frequency or the original waveform. When the AM signals come in the envelope detector, the signal been filter and get back the original waveform or low frequency signal.

After pass thru the envelope detector, the signal is analog signal. PIC need stable digital data to process and decode the data correctly. So the decision circuit is needed in this project for convert the analog signal to stable digital signal.

After tested overall circuit, the message can be transmit successfully and correctly with ASK.

Chapter 6: Problems & Solutions

6.1 Hardware Problem & Solution

6.1.1 Op-amp

Problem: Op-amp LM741 getting the output of 1.78V when it is low. The expected result should be close to 0V.

Solution: Change the LM741 to LM10 that get the output voltage very close to 0V.

6.1.2 PIC

Problem: The PIC sometimes cannot send and receive the data correctly. There was some floating for the other unused pins.

Solution: Grounded all the unused pins.

6.1.3 Diode

Problem: Cannot get the germanium diode.

Solution: Replace with normal diode 1N4148.

6.2 Software Problem & Solution

6.2.1 Key map

Problem: The key map consists too much character when include the capital letter. User need to press so many time to get the correct alphabet.

Solution: Remove the capital letter from key map and just left the small letter make the key map more simple.

6.2.2 Data rate

Problem: Cannot get the fast data rate due to the limitation of PIC. If the data rate go higher than 500 bits/s, the data cannot receive correctly.

Solution: Set the data rate to 200 bits/s for this short message transmission. For transmit the maximum data 40 character just need 2 seconds.

Chapter 7: Future Development

In future, the data rate can increase with using other devices to transmit like computer or other microcontroller with higher clock pulse. Do the two way connection either in half duplex or full duplex and implement the error checking to ensure the data is send correctly. Parity bit is the one of the simplest way of doing the error checking. Rather than use ASK, can use FSK or PSK to sending the data.

Chapter 8: Conclusion

The Amplitude Shift Key Codec at 40.68 MHz is the project that code and decode the digital data and send the data with Amplitude Shift Key. The project aims and technical objectives were achieved. The transmitter can get user input and code it to send in ASK method. At the receiver, the ASK signal can be detect and decode correctly. The result getting is exactly same as what was expected. This project is successfully been done.

The project's objectives were achieved as shown below.

Technical Objectives

Status

To acquire digital data input from keypad using microcontroller

Status achieved. Users can key in message using keypad with alphanumeric input.

Encode the digital data using ASK for wireless transmission

Status achieved. The message is transmitted using ASK signal thru signal generator at 40.68MHz

Detect ASK signal at the receiver

Status achieved. ASK signal can be detect by the envelope detector and recover back the waveform.

Create a suitable method for symbol timing recovery

Status achieved. The microcontroller can decode the data correctly with start & stop bit.

To read the digital data correctly at receiver

Status achieved. The message can receive correctly.

Display the data on LCD

Status achieved. The message received successfully display on LCD.

Table 5: Table Objectives & Status