FM Transmitter Dec06-01

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FM TransmitterDec06-01 Client Iowa State
University Senior Design Team Grant
Blythe Luke Erichsen Tony Hunziker Jacob
Sloat Advisors Dr. John W. Lamont Prof. Ralph E.
Patterson III
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Definitions

• FCC Federal Communication Commission
• LCD liquid crystal display
• MP3 player digital music player, (i.e. ipod)
• Satellite radio subscription radio signal sent
  via satellite, (i.e. XM radio, Sirius radio)
• Transmission frequency The frequency at which
  the device is transmitting the FM modulated
  signal to the FM radio.
• Wall wart AC power transformer designed to plug
  into a standard wall outlet

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General Problem Statement

• The objective of this project is to design a FM
  transmitter that will
• Connect to a standard headphone output jack of an
  mp3 player
• Transmit a minimum of 12ft
• Transmit between frequencies of 88MHz to 108MHz
• Have 4 programmable preset buttons
• Receive power from a cigarette lighter/power
  socket
• Automatic on/off function

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General Solution Approach

• The FM transmitter will modulate the signal, send
  it through an amplifier, and finally through an
  internal antenna.

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General Solution Approach

• Internal memory will store four programmable
  station presets from the frequency band.
• A LCD screen will display the current
  transmission frequency. This LCD will be backlit
  for easy night use.
• The transmission frequency and presets will be
  accessible through a button/knob interface that
  may also include a lighting system.
• There will be a microcontroller to access memory,
  automatic turn off/on function, possible
  lighting, display frequency, and any other
  controlling concerns.

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Operating Environment

• The finished device will operate within a
  personal vehicle or a household room that could
  be exposed to
• Moisture
• Dust
• Dirt
• Impacts
• Reckless negligence

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Intended User(s) / Use(s)

• Intended User(s)
• The intended user for this product is anyone
  owning MP3 players or satellite radio devices.
  It does assume the amount of operating knowledge
  associated with MP3 player/satellite radio users.
  
• Intended Use(s)
• The FM transmitter is intended to make personal
  music players more accessible to listen to
  through home and car stereos.

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Assumptions

• The transmitter will be used for all varieties of
  personal music players.
• The transmitter will be used in a variety of
  environments including varying temperatures,
  humidity, seismic conditions, and electromagnetic
  noise.
• The transmitter will be used at all hours of the
  day.
• Similar products will come directly from the
  personal music players producers as competition.

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Assumptions Continued

• The device will be used with standard North
  American FM radio equipment.
• The input audio signal will consist of standard
  music with a frequency range of 20 Hz to 20 kHz.
• The device design will implement solid state
  electronics.
• The user will have access to a steady power
  source able to supply the rated voltage and
  frequency (if AC) within a 10 percent tolerance.

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Limitations

• The cost to purchase this product shall not
  become uncompetitive.
• The transmitter must conform to FCC regulations.
• The FCC has regulation broadcast strength of
  .1kW. The transmitter must not exceed this
  strength.
• The device shall conform with FCC rules Part 15
  concerning unlicensed FM broadcasting.
• The RF field strength 3 meters from the device
  should not exceed 250uV/m.
• The transmission frequency band must stay within
  88-108 MHz.
• The device shall be capable of obtaining power
  from both a 120 V AC and a 12 V DC source.

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Limitations Continued...

• The form of the device must be manageable for
  ease of transportation and storage.
• There must be at least 4 programmable preset
  transmission frequencies.
• The device must transmit at least 12 feet.
• Transmission frequency must be adjustable.
• Transmission frequency must be displayed.
• The size shall not exceed 6 in. by 6 in. by 3 in.
• The weight shall not exceed 1 lb.
• The device shall be compatible with both digital
  and analog tuned radios.

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Expected End-Product

• The device case will be made of plastic
• The case will allow for easy hand manipulation
  and transportation
• The device will implement an LCD screen
  displaying the transmission frequency.
• The user input interface will consist of six
  buttons.
• up and a down button to adjust transmission
  frequency
• 4 buttons will each access a programmable preset
  frequency

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Detailed Functionality

• Pushing and releasing a preset button, in less
  than 3 seconds, will adjust the transmission
  frequency to the stored frequency assigned to
  that button.
• Pushing and holding a preset button for greater
  than 3 seconds will assign and store the current
  transmission frequency to that preset button.
• Both the LCD display screen and the buttons may
  be backlit for use in low ambient light
  environments.
• This device shall come with an adapter for use
  with an American standard wall outlet. This will
  be a simple wall wart device. The output from
  this adapter will be a male power jack.

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Detailed Functionality Continued

• The transmitter will also come with an adapter
  for the standard cigarette outlet for automobile
  use. The output of this adapter will be a male
  power jack.
• Both adapters will connect to the device through
  a common female jack. The adapters will be
  designed so that the device will receive the same
  power input regardless of which adapter is being
  used.
• An instruction manual will also be included.
• The device and accessories should be deliverable
  by December 2006.

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Detailed Design

• This includes the different systems within the
  design, the parts currently considered to
  implement these systems, and preliminary prices
  of these components.

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Inputs

• Manual Inputs
• These inputs allow the user to adjust and fine
  tune the transmission frequency manually.
• There will be two buttons for the manual input
  function.
• one to adjust the transmission frequency up and
  one button to adjust the transmission frequency
  down.
• Adjustment of the transmission frequency will
  happen in increments of 200 kHz.
• For example 102.7 MHz will increase to 102.9 MHz
  or decrease to 102.5 MHz in response to the
  received input.

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Inputs Continued

• Preset Inputs
• The four programmable preset frequencies shall be
  stored in non-volatile memory in the device.
• The transmission frequency shall be adjusted to
  any of these frequencies by pushing one of the
  four corresponding buttons.
• A preset shall be programmed to the current
  frequency by pushing and holding the
  corresponding button for greater than 3 seconds.
  
• These four buttons will be backlit for use in low
  light environments.

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Inputs Continued

• Power Supply
• The device shall receive its power input from a
  12 V DC cigarette lighter/power socket in an
  automobile or a standard 120 V AC wall outlet.
  An adapter will be provided for each of these two
  sources.
• Both adapters will provide a common 5 V DC output
  to the device.
• The device will have one power input jack that
  will be capable of connecting to either adapter.

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Inputs Continued

• Power Supply Continued
• The adapter for the cigarette lighter will be a
  single stage adapter that plugs directly into the
  standard cigarette lighter/ power outlet of an
  automobile.
• The adapter will convert the 12V output of the
  cigarette lighter to the 5V DC input needed for
  the device
• The source from the wall outlet will be a wall
  wart
• Converts the 120V AC to a 5V DC output
• Provided by the EE/CprE Senior Design

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Inputs Continued

• Input Signal
• The input signal may come from an mp3 player, or
  a satellite radio system.
• The audio signal input is expected to consist of
  audio frequencies within the range of 20Hz to 20
  kHz.
• The device shall accept a stereo input audio
  signal through a standard 3.5 mm stereo jack.

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Processing

• Microcontroller Design Requirements
• It will take in the manual and preset inputs and
  tune the device to a transmission frequency
  depending on which buttons are pushed.
• It will allow the device to store transmission
  frequencies into the preset buttons.
• It will also implement the auto turn on/turn off
  function with respect to the input signal.
• The LCD display will also be controlled by the
  microcontroller.

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Processing Continued

• Microcontroller Solution
• The PIC processor PIC16F873A was chosen along
  with the LM555 clock.
• It contains a 28 pin IO interface and the memory
  and processing power needed for our application.
  
• PIC processors will give us the necessary
  computing power to control all components of the
  device including the LCD.
• At the same time PIC processors are inexpensive
  and will fall within the project budget.
• PIC processors also possess the non-volatile
  memory necessary to store the preset stations.

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Processing Continued

• Microcontroller Solution Continued

PIC16F873A Microcontroller
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Processing Continued

• Auto On/Off Implementation
• The microcontroller will be in a continuous loop
  awaiting the input in order to control the
  peripherals.
• Upon detection of an input signal, the device
  shall power on and begin transmitting within 1
  second.
• After detecting no input signal for 1 minute, the
  device shall power down within 1 second.
• This count down is a period to wait for signal
  before actually powering down. This prevents
  premature power down.

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Modulation/Transmission

• Modulation/Transmission Block
• After examining the available technologies, an
  integrated solution was found to provide the
  modulation, amplification, and transmission.
• The device will implement a Rohm Electronics
  BH1415F Wireless Audio Link IC to provide stereo
  modulation and FM transmission.

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Modulation/Transmission
Rohm BH1415F
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Modulation/Transmission

• Rohm BH1415F
• The BH1415F consists of a stereo modulator for
  generating the stereo composite signal and a FM
  transmitter for broadcasting an FM signal on the
  air.
• The IC transmits on a frequency range of 88 MHz
  to 108 MHz. The transmission frequency is set by
  the microcontroller.

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Modulation/Transmission

• Composite Stereo Signal

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Modulation/Transmission

• FM Modulation
• The composite stereo signal is then modulated
  with a carrier signal.
• This carrier signal is the frequency you tune to
  with an FM radio.
• The carrier signal is set on the BH1415F by the
  microcontroller using a data packet.

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Modulation/Transmission
Data Packet to BH1415F
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Modulation/Transmission
Carrier Frequency Data For Example in the case
of 99.7 MHz carrier frequency. 99.7 MHz / 100
kHz (fref) 997 ? 3E5 (HEX)
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Outputs

• There are two outputs from the device.
• An LCD screen that will display the frequency
  that the device is currently transmitting at.
• The other output is the FM audio output
  transmitted by the antenna.

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Outputs Continued

• LCD Display Requirements
• When a frequency change occurs, the
  microcontroller will send the appropriate control
  signals to the LCD display.
• Each of the 4 digits plus the decimal point
  displayed will be controlled individually, and
  will only need to be refreshed when the frequency
  is change.
• The format of this display will be XXX.X (i.e.
  102.7).
• The display is also backlit.

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Outputs Continued

• LCD Display Solution
• The LCD chosen was the VIM-404-DP-FC-S-HV LCD
  manufactured by Varitronix.
• It is a transflective backlit display
• The way it accepts inputs is dependant upon its
  programming making it a versatile choice.
• Its 20 I/O pin interface is typical for LCD
  components on the market.

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Outputs Continued

• LCD Display Solution

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Outputs Continued

• LCD Display Solution

Pin COM1 COM2 COM3
1-3 N.C. N.C. N.C
4 1B 1C 1P
5 2B 2C 2P
6 3B 3C 3P
7 4B 4C ---
8 --- --- COM3
9-10 N.C. N.C. N.C

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Outputs Continued

• Antenna
• The device will use a small wire antenna that
  will remain inside the device case. Because the
  case is plastic and the transmission range is
  small, there should not be a need for an external
  antenna.

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Overall Schematic
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Unforeseen Issues

• Display
• Interfacing with microcontroller
• Rohm BH1415F Wireless Audio Link IC
• Phase Lock Loop

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Questions?