Final presentation for Minor Project completed by BEX Third year students of Thapathali Campus, IOE.

1. BLUETOOTH CONTROLLED
HIGH POWER AUDIO
AMPLIFIER
Thapathali Campus
Final Presentation
2013
PRESENTED BY:
BIJAY RAJ PAUDEL (ROLL NO: 067/BEX/105)
SAGAR MALI (ROLL NO: 067/BEX/133)
SUJAN SHRESTHA (ROLL NO: 067/BEX/140)

2. INTRODUCTION
• Decent quality High Power Audio Amplifier
• 8051 Microcontroller based control
• Digital control over tone, effects & volume
• Wireless Bluetooth Interface
• Control via Computer Software/ Android
software and/or Keypad

3. OBJECTIVES
• To construct cost effective high power audio amplifier.
• To implement 8051 μc along with it’s interfacing.
• To control the system via wireless Bluetooth module.
• To program μc & develop GUI based PC application.
• To improve our programming & practical skills.

4. PROJECT IN BLOCK DIAGRAM
MAIN BOARD
Audio Input

5. PROJECT IN BLOCK DIAGRAM
CONTROLLING UNIT

6. BRIEF EXPLANATION OF EACH BLOCK
BLOCK
REPRESENTAION
OF
POWER SUPPLY

7. BRIEF EXPLANATION OF EACH BLOCK
1. POWER SUPPLY
1.1. RECTIFIER
• 6A capacity bridge rectifier with
+43 and -43 volt output
• With Electrolytic and Ceramic
capacitor filer
• 5A fuse for protection

8. BRIEF EXPLANATION OF EACH BLOCK
1.2. VOLTAGE REGULATOR
• Based on LM337
(negative voltage regulator)
and LM137
(positive voltage regulator)
• Conduction through
Power transistors for increased
current capacity.

9. BRIEF EXPLANATION OF EACH BLOCK
2. PRE AMPLIFIER
• 3 active filters( for bass, mid, treble)
• 2 op-amp amplifiers first before filter
& next after filter for larger gain.
• Variable Gain controller
• In-built Distortion effect
(achieved by diode clipping)

10. BRIEF EXPLANATION OF EACH BLOCK
3. DIGITAL VOLUME & TONE CONTROL
• Based on analogue multiplexers. (8x1 for bass, mid,
treble and 16x1 for volume control)

11. BRIEF EXPLANATION OF EACH BLOCK
4. POWER AMPLIFIER
• Simulated for 80Watt output in Proteus,
(power supply of +-30 V)
• 3 stage amplifierDifferential amplifier input (for gain)
Voltage amplifier
Power amplifier
• Output short circuit protection

12. BRIEF EXPLANATION OF EACH BLOCK
5. Bluetooth Module
•Uses class C Bluetooth radio
•Uses SPP (Serial Port Protocol) for interface
•4 pins for Vcc, Gnd, Txd and RxD
•Works at default baud rate of 9600 bauds
•Interface with 8051 microcontroller using UART
•Works at CMOS voltage level (3.3V, 0V)

13. BRIEF EXPLANATION OF EACH BLOCK
6. TTL – CMOS level Converter
•Bluetooth works on CMOS level and microcontroller on TTL level
so voltage level conversion is required.
•Achieved by using N-Channel Enhancement mode MOSFET
•Bidirectional operation (3.3V to 5V and 5V to 3.3V)
•Two similar circuits for TxD and RxD

14. COMPUTER GUI
• Codes in C# .NET
• Uses serial port class provided by .NET library
• User interface in WPF

15. BRIEF EXPLANATION OF EACH BLOCK
4. Main Controller Board
•8051 microcontroller based
•Interface with LCD in 8 bit mode
•Interface with EEPROM
•Interface with three 8x1 analogue
multiplexers for bass, mid, and treble
control and one 16x1 multiplexer for
volume control
•Interface with Bluetooth module

16. ALGORITHM FOR MAIN CONTROLLER

17. START
Initialize LCD
Show Welcome bass, mid, Volume & treble status
Initialize Serial Port in mode1 and Set Timer 1 for 9600 baud in mode 2
Set Timer 0 value and enable timer 0 interrupt
Enable timer 0 and timer 1
While
(1)
Timer 0
Interrupt
Update LCD with
Bass, mid, treble
and volume’s
current value
Check
interrupt
C
Serial
Interrupt
SI

18. SI
Yes
C
TI=0
Is TI set?
Check Keypad Pins
No
Increase/Decrease volume,
bass, mid and treble
Send data corresponding pins
attached to multiplexers
Send updated values to serial
port(SBUF)
No
Is RI set?
RI=0
Yes
Read SBUF serial port
RI ≠0
Update Vol, Bass, Mid Treble value
as command received in SBUF
Send data to corresponding
pins attached to multiplexers

19. BRIEF EXPLANATION OF EACH BLOCK
4. KEYPAD
• 4*4 matrix keypad.
• 16 keys produce 16 different
combinations to interface with the
main controller
• Extra interrupt signal pin
• Backlight LEDs for low light operation

20. BRIEF EXPLANATION OF EACH BLOCK
5. KEYPAD CONTROLLER
• Separate Controller to scan keys to
relieve main controller of input reading
duties
• 8051 microcontroller based
• Accepts the input from keypad
• Outputs information to microcontroller
at main board

21. ALGORITHM FOR KEYPAD CONTROLLER

22. START
Similar to other columns &
rows
Initialize all ports to zero
Output 5 to port 1
Is key
pressed?
Is R1=0?
Yes
Initialize all rows to 1
Initialize C2 =0 & other to 1
Initialize C1=0 other to 1
Similar to other rows R2 to R4
Is R1=0?
Output 0 to port 1

23. PROBLEMS
SOLUTIONS
•
Using transistors in metal
cases and larger heat sinks
•
Proper shielding of
preamplifier and connecting
wires
• Speaker over voltage
•
spikes damaging the
speaker under high
volumes
Use of filter output capacitor
and output audio
transformer(yet to be
implemented
•
Use of analogue mux, with
lesser resolution but it does
the job
• Overheating of power
transistors
• Noise induction in
preamplifier.
• Digital potentiometer not
available

24. APPLICATIONS
• Auditorium Hall
 Seminar
 Presentation
 Lecture
• Theatrical and Concert sound
reinforcement
• Home Theater System
• Car Audio System
• Guitar Amplification

25. PROPOSED BUT NOT IMPLEMENTED PARTS
• Limited effect is only implemented because of unavailability of
effect IC and complex design if done using discrete
components.
• Separate independent remote control with LCD
Couldn’t be implemented because of high cost of Bluetooth module.
Making separate controller required another Bluetooth module working
in Master mode.
Bluetooth of laptop or android set is used as Master (Host).

26. EXTRA PARTS IMPLEMENTED
• Interface using Android devices (tablets and smart phones)
• High current capacity voltage regulator
• TTL-CMOS bidirectional voltage level converter

27. CONCLUSION
•
•
Our final product is HIGH POWER AUDIO AMPLIFIER.
•
Finally, it has it’s own GUI BASED CONTROL APPLICATION which
can be operated through Bluetooth enabled windows based
devices.
•
Control via Android based smart-phones using serial terminal
emulator for android (BlueTerm)
We have build BLUETOOTH INTERFACE between system & digital
control.

28. FURTHER ENHANCEMENT
• Multichannel audio output (2.0 ch, 5.1ch)
• Wireless audio input via Bluetooth.
• Increasing steps for tone and volume control.
• Development of control applications on other platform
(iOS, Mac, Linux )
• Other audio effects (Echo, delay, compression, reverb
etc.)

29. REFERENCES
BOOKS:
•
A.S. Sedra and K.C. Smith, “Microelectronics Circuits Theory and Application”,
5th edition, Oxford University Press
•
Muhammad Ali Mazidi, “8051 Microcontroller and Embedded Systems”,
Prentice Hall, 2006
•
Douglas Self, “Audio Power Amplifier. Design Handbook”, 3rdedition.
WEBSITES:
•
•
•
•
•
http://hackaday.com/2011/06/27/stereo-amplifier-with-digital-volume-control/
http://www.diyaudio.com/forums/solid-state/
http://en.wikipedia.org/wiki/Bluetooth
http://www.bluetooth.com/
http://www.aaroncake.net/circuits/volume.asp

30. THANK YOU
FOR YOUR INTEREST!