Wireless MP3 FM Transmitter

1
Wireless MP3 FM Transmitter

• Group 17
• Anh Huynh
• Kwitae Kim
• Jung Suh
• EEL 4915 Senior Design II
• Dr. Richie
• Spring 2003

Self-sponsored Project
2
Overview

• Intro - Anh
• Transmitter - Jung
• Circuit Design - Kwitae
• Prototype Testing - Anh
• Summary - Anh

3

• Introduction
• Anh

4
Project Description

• Wireless MP3 FM transmitter is a device that will
  enable MP3 audio playback through any FM stereo.
• Device will transmit any MP3 audio output to any
  FM stereo located within the operating range.
• Allows the user to listen to MP3 music through
  higher quality speakers vs standard computer
  speakers.

5
Project Motivations

• Popularity of MP3 audio format
• Low cost
• Versatile
• Easy to use
• No programming needed

6
Project Objectives

• Variable transmitter frequency
• Adequate user range
• FM stereo transmission
• Compact
• Light weight
• Wireless data transmission
• Low power consumption

7
General Diagram
3.5mm Stereo Cable
FM Transmission
MP3 Audio Source
MP3 Tx
Receiver
Music
User
(Doing the worm)
8
Block Diagram
DC Power
FM Modulator
MPX Modulator
Pre-emphasis
Audio Input
Buffer Amp
Carrier Osc
Freq. Multiplier
RF Amp
Antenna
Receiver
9
Reasons for FM Tx

• Wireless FM link between the PC and home stereo
• FM Tx allows
• A flexible product
• Requires no line of sight by receiver
• Plug-n-Play, no software required
• FM scheme
• Popular method of audio transmission
• Inexpensive transmitters
• Compatibility to preexisting technology

10
Features

• 3.5mm stereo plug compatible with most audio
  devices (PC, MP3 Stereo, Portable MP3 player)
• Tune your home or portable FM radio to the same
  frequency
• Hear your favorite music in full-stereo sound
• Works with all MP3 players

11
Specifications

• Variable frequency range 88 98 MHz
• Supply Voltage 9V DC adapter
• Device dimensions 6x3x3 (WHD)
• Weight Less than 1 lbs.
• Transmission Range 30 m (unobstructed)
• Input Jack 3.5mm stereo plug

12
User Benefits

• Eliminate need to buy costly computer speakers
• Multipurpose use
• Extends MP3 audio playback capabilities
• Compatible with home stereos

13
How to Use

• Easy, basically plug-and-play
• Turn on audio source, Tx, Rx
• Connect audio source to transmitter using audio
  cable
• Tune intended receiver to match Tx frequency
• Play audio source
• Listen to music

14
FCC Compliant

• According to
• Title 47 - Telecommunication
• Chapter I - Federal Communications Commission
• Part 15 - Radio Frequency Devices
• Subpart C - Intentional Radiators
• Section 15.239 - Operation in the band 88 -
  108MHz
• Yes, Transmitter is FCC Compliant

15
Transmitter (I/C)by Jung Suh
16
Transmitter Chip Requirements

• Has to be stereo transmitter (stereo modulation)
• Appropriate in-built systems
• (Multiplexer, Filters, RF Amplifier,
  Crystal Oscillator)
• Easy interfacing with other components
• Cost issue
• Under 20 range

17
Chip Comparison - 1

• BA1404
• Made by Rohm Corp.
• Stereo FM Transmitter
• Pro
• requires low voltage
• requires few external components
• Con
• RF oscillator is little unstable (some times it
  drifted)

• MC2833
• Made by Motorola
• Stereo FM Transmitter
• Pro
• very low drain current
• requires few external components
• Con
• high voltage required

18
Chip Comparison - 2

• NJM2035
• Made by New Japan Radio Corp.
• Stereo FM Transmitter
• Pro
• requires low voltage
• requires few external components
• Con
• Low voltage gain

19
Technical Comparison -1
20
Technical Comparison -2
21
Why BA1404 (DIP18) ?

• Equipped with a constant voltage pin
• (variable capacitor that is used to finely
  adjust the FM frequency)
• Low required voltage
• Low power consumption
• More resources available
• Available in DIP18 packages

22
BA1404 Description

• The IC consists of a stereo modulator (creates
  stereo composite signals), an FM modulator
  (creates FM signals), and an RF amplifier.
• The stereo modulator develops composite signals
  made up of a MAIN (LR) signal, a SUB (L_R)
  signal and a pilot (19 KHz) signal using 38 KHz
  crystal oscillators.
• The FM modulator has carriers on the FM
  broadcast band.
• The RF amplifier transmits the stereo encoded FM
  signals and is also a buffer for the FM
  modulator.
• The stereo transmitter is equipped with a
  constant voltage pin for a variable capacitor
  that is used to finely adjust the FM frequency.

23
BA1404 Specifications

• A 38 KHz crystal derived stereo modulation (by
  crystal oscillator)
• Operating Voltage Range 1.0V 2.0V
• Power Consumption typically 3mA
• The transmission frequency is stable because it
  has a PLL Phase-Locked Loop)

24
BA1404 Specifications pin out
Reprint with permission pending from ROHM
Corporation
25
BA1404 Specifications pin out description
26
BA1404 Specifications pin out description
(cont)
27
BA1404 Dimensions
(Unit mm)
Reprint with permission pending from ROHM
Corporation
28
Chip Operation

• Stereo Modulator
• FM Modulator
• Crystal oscillator
• RF oscillator

29
Stereo Modulator

• The R-channel audio is input from pin 1 and the
  L-channel from pin 18.
• Each audio signal is amplified about 37 dB by
  independent amplifiers and output to the
  multiplexer.
• The 38 kHz crystal oscillator, connected between
  pin 5 and pin 6, creates a 38 kHz subcarrier and
  a 19 kHz pilot signal.
• The audio signals and the 38 kHz subcarrier are
  balanced and modulated in the multiplexer.
• The LR signal and the 38 kHz subcarrier are
  added to create the main carrier, which is output
  from pin 14.

30
FM Modulator

• The composite signal is input from pin 12 to the
  base of the transistor.
• By changing the time constant of the tuning
  circuit in the oscillator, the frequency is
  modulated.
• The oscillation frequency is determined by the
  LC resonator .
• It is possible to change the oscillator
  frequency with DC voltage by using the stable
  output voltage on pin 11 and a variable capacitor
  

31
Stereo Modulator - Schematic
Reprint with permission pending from ROHM
Corporation
32
Crystal Oscillator

• Use to generate the 38 KHz carrier signal.
• Start-up takes some time after the 38 KHz
  oscillator has been powered up.
• With a recommended load of 10 pF for the crystal
  oscillator, startup time approximately 1.5 sec.
• When the load is 33 pF, startup time is about 1
  sec.

33
RF oscillator

• The built-in FM modulator can be operated in the
  30110 MHz range.
• The RF oscillator frequency drift following
  power-up of the power supply becomes small when
  the Vcc is low.
• Frequency drift after 5 sec is as follows
• Vcc (V) Drift (kHz)
• 1.25 85
• 2 85
• 3 130

34
Chip Noise

• If beats or noise are present on the output, and
  the input capacitors are in place, the noise may
  be due to the third or higher harmonics from the
  pilot signal and the subcarrier.
• In addition, high frequency signals are
  particularly large because of the pre-emphasis of
  high frequency signals.
• Therefore excessive input of 15 KHz frequencies
  or more should be limited before input to the IC.
• We can also connect 1000pF capacitors on pin 1
  and 18 to ground to prevents the S/N ratio from
  deteriorating due to high frequencies.

35
Circuit Designby Kwitae
36
Types of Modulation(Methods to generate the
carrier frequency)

• AM
• Simple
• Least expensive
• Susceptible to interference

• FM
• Better Range
• Less Interference
• Popular Freq. Range

• PCM
• (Pulse-Coded Modulation)
• Greater Range
• Not widely used
• More costly

37
Power supply Design

• Input ? 9V
• Output ? Regulated 6V
• Need to be filtered well
• On board adapter jack

38
Design approach

• Often unwanted hum appears on the transmitted
  signal
• Power supply hum due to poor DC supply filtering
• Need to have almost zero-ripple at the output to
  prevent the hum which is caused by the 60 HZ AC
  line oscillation

39
Power Supply Schematic
40
Transmitter Design

• Pre-emphasis
• Crystal Oscillator
• LC Resonator
• RF amplifier
• Antenna

41
BA1404 Application
Reprint with permission pending from ROHM
Corporation
42
Pre-emphasis

• High-pass filter
• Accentuate high frequencies
• Improves SNR, boosts treble

43
Basic Pre-emphasis filter
44
Basic De-emphasis filter
45
Transmitter Circuit
46
Antenna Comparison

• Wire antenna
• Low cost
• Variable length
• Widely available
• Easy to install

• Loop Ant
• More costly
• Size limitations
• Space consuming

47
Antenna Calculations

• 1/4 Wavelength
• Example 95MHz Frequency
• ? (cm) c / f
• 3 x 10 10 (cm/s) / 95 x 10 6 Hz
• 315.79 cm
• Antenna length should be 315.79 / 4 78.95 cm
• Max. Ant. length at 88MHz 85 cm
• Will Use 85 cm Antenna

48
Transmitter Power

• Tx Pwr 3V 3mA
• Tx Pwr 9 mW
• 9mW 31m transmission distance
• Which meets requirements

49
Prototype TestingAnh
50
Parts Used
51
Initial Prototype

• Top View

52
Initial Prototype

• Bottom View

53
Prototype Testing

• First audio test

54
Complications

• Weak signal of the receiver input
• Variable inductor difficult to tune
• Several components very sensitive to external
  interference
• Excess noise on the transmitted signal

55
Solution to FM Noise

• Current Solutions
• Re-adjust the variable inductor
• Re-adjust the variable resistor
• Check proper voltage input
• Additional Solution
• Mount the components on a PCB

56
Testing Data
57
Testing Results

• 1st Test Did not work, low signal, high
  distortion
• 2nd Test It worked!, strong signal, low static
• 3rd Test Did not work, lots of noise, low
  signal
• 4th Test Success! It worked almost flawlessly
  for over two hours of continuous
  operation. Its a miracle

58

• Summary
• Anh

59
Work Division
60
Milestone
61
Current Progress
62
Budget
63
Current Status

• Completed PCB milling tutorial
• Assembled initial prototype
• Initial Prototype fully functional
• Currently working on PCB layout using P-CAD

64
Objectives To Be Completed

• Testing and analysis
• PCB layout and milling
• Final prototype assembly
• Final testing
• Final presentation
• Final document

65
Final Words

• Final prototype ready by late March

66
Questions?