Design Review by xiangpeng


									FM Transmitter

Iowa State University – Senior Design

 Grant Blythe        Luke Erichsen
  Tony Hunziker         Jacob Sloat

        Dr. John W. Lamont
     Prof. Ralph E. Patterson III
 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
 Wall wart: AC power transformer designed to plug into a
  standard wall outlet
     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
   Have 4 programmable preset buttons
   Receive power from a cigarette lighter/power
   Automatic on/off function
       General Solution Approach
   The FM transmitter will modulate the signal, send it through an
    amplifier, and finally through an internal antenna.
       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.
          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
       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.

   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.
        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.
   The cost to purchase this product shall not become
   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.
       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.
           Expected End-Product

   The device case will be made of plastic
   The case will allow for easy hand manipulation and
   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
           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.
    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.
             Detailed Design
This includes the different systems within the design, the
parts currently considered to implement these systems,
and preliminary prices of these components.
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.
             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
             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.
              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
          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.
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
          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.
     Processing Continued…
Microcontroller Solution Continued…

            PIC16F873A Microcontroller
          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.
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.
Rohm BH1415F
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
Composite Stereo Signal
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.
Data Packet to BH1415F
Carrier Frequency Data

For Example: in the case of 99.7 MHz carrier frequency.

99.7 MHz / 100 kHz (fref) = 997  3E5 (HEX)

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.
           Outputs Continued…
LCD Display Requirements

 When a frequency change occurs, the microcontroller
  will send the appropriate control signals to the LCD
 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.
          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.
       Outputs Continued…
LCD Display Solution
        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
         …      …      …      …
            Outputs Continued…

   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.
Overall Schematic
              Unforeseen Issues
   Interfacing with microcontroller

Rohm BH1415F Wireless Audio Link IC
   Phase Lock Loop

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