Continuous Playback FM Transmitter

1
Continuous Playback FM Transmitter
A new concept in advertising.
2
Team Members

• Team leader
• Joseph Massey
• Group members
• Melissa Bourg
• Craig Ivey
• Charles Ingram
• Faculty Advisor
• Dr. Pat Donohoe

3
Overview

• Problem Businesses do not have an efficient
  method of advertising to nearby automobile
  passengers.
• Solution Develop a low-power radio transmitter
  that will relay a customizable message to an
  automobile receiver.

4
Solution

• Design a transmitter that will continuously play
  back advertisements in the FM broadcast band
  (87.7-107.9 MHz).
• Develop a circuit that will be efficient and as
  powerful as possible without exceeding FCC part
  15 regulations.

5
Design Constraints

• FCC Requirements The transmitter should meet all
  FCC Part 15 rules and regulations.
• 250µV/m measured at 3 meters
• 200kHz bandwidth and frequency spacing
• 20 dB attenuation on spurious signals
• Operating Frequency Transmitter should be
  tunable to selected frequencies on the FM
  broadcast band from 87.7 - 107.9 MHz.
• Range and Clarity Reception range should be at
  least 200 feet.

6
Design Constraints

• Signal Stability The FM signal should remain
  stable and not drift outside the 200KHz band.
• Size and Weight the completed device should
  weigh less than 16 ounces and fit into a 4x 3x
  2 project box.
• Power Requirements The circuit should operate on
  a 12 VDC, 1A wall adapter.

7
Design Constraints

• Audio Capacity The recording IC should store at
  least a 30 second audio message.
• User Interface The device will be controlled by
  a start button, a stop button, and a
  record/playback mode switch.
• Target Cost The high-volume parts cost should be
  under 30.

8
Diagram of Hardware
9
Development Plan
Hardware Design
Determination of Components
Draft Schematic
Voice Recorder Configuration
FM Transmitter Configuration
Simulation
Simulation
Hardware Testing
Hardware Testing
Integration
Final Testing
10
Diagram of Hardware
11
Control Timer

• In record mode, Start button begins the
  recording, Stop button ends the recording
• In playback mode, Start button begins playback
• Playback is continuous
• Recording buffer will not overflow

12
Control Timer Schematic
Monostable CD4528 Timer
13
Control Timer Schematic
Monostable CD4528 Timer
14
Control Timer Waveform
Playback Activates
Playback Reactivates
Start Button Pressed
Message Ends Timer Resets
15
Diagram of Hardware
16
Digital Voice Recorder

• ISD2560
• 60 second capacity
• Compatible with 120 second version

17
Diagram of Hardware
18
FM Transmitter IC

• Rohm BH1417F
• Frequency Range Limited to
  87.7-88.9 MHz and 106.7-107.9 MHz
• Phase-locked loop
• Resolves the signal stability and frequency
  selectivity design constraints

19
Transmitted Signal

• 59 dBuV signal strength at output
• 50 ohm impedance
• 150 kHz Bandwidth

20
Diagram of Hardware
21
Lowpass Filter FCC Requirements

• Part 15 Rules Regulations
• 20 dB attenuation on spurious emissions
• No interference to licensed stations
• Problem TV channels 7 13 occupy 2nd
  harmonic frequency range.

22
RF Lowpass Filter
From Transmitter IC
To RF Amplifier
7th-Order Chebyshev
23
Lowpass Transfer Curve
FM Broadcast Band
24
Diagram of Hardware
25
Antenna

• Short Loop Antenna
• Directional
• Gain -3.25 dB
• Length 23.5 circum.

26
Antenna Radiation Pattern
27
Antenna Matching Design

• 23.5 circumference, 8 gauge copper wire
• Input Impedance Z0.559 j346 ?
• Not matched to 50 ?! But we can eliminate the
  jX.
• C1/(2?88.5MHz346?) 5 pF
• Place a 5 pF capacitor in series with the antenna.

28
Antenna Matching Design

• More Tuning Issues
• Perfect match SWR 11

• Feed line will not match the antenna impedance
• FM Transmitter will tolerate a high SWR

29
Antenna FCC Requirements

• E Sqrt( 30 x Power x Gain ) / Distance
• Power 20 nW
• Antenna Gain -3.25 dB 0.473
• FCC Measurement Distance 3 meters
• E 178 uV/m

30
Antenna Range

• Distance Sqrt(30PG) / Sensitivity
• FM Receiver Sensitivity 2.0 uV/m
• Distance 874 feet

31
Design Constraints vs. Results
32
Design Constraints vs. Results
33
Design Constraints vs. Results
34
Design Constraints vs. Results
b
35
Design Constraints vs. Results
b
36
Diagram of Hardware
Voltage Controlled Oscillator (VCO)
VCO Adjust
37
Diagram of Hardware
Voltage Controlled Oscillator (VCO)
VCO Adjust
38
Design Constraints vs. Results
b
39
Design Constraints vs. Results
b
r
40
Design Constraints vs. Results
b
r
41
Design Constraints vs. Results
b
r
42
Design Constraints vs. Results
b
r
b
43
Design Constraints vs. Results
b
r
b
44
Design Constraints vs. Results
b
r
b
45
Design Constraints vs. Results
b
r
b
r
46
Design Constraints vs. Results
47
Power Requirements

• ISD2560 Voice Recorder 18 mA
• BH1417 FM Transmitter 23 mA
• Total 41 mA

48
Design Constraints vs. Results
49
Design Constraints vs. Results
b
50
Design Constraints vs. Results
b
51
Design Constraints vs. Results
b
52
Design Constraints vs. Results
b
b
53
Design Constraints vs. Results
b
b
54
Design Constraints vs. Results
b
b
55
Design Constraints vs. Results
b
b
b
56
Design Constraints vs. Results
b
b
b
57
Major Component Costs
58
Design Constraints vs. Results
b
b
b
59
Design Constraints vs. Results
b
b
b
b
60
Circuit Board Layout
2.5
3.9
61
Timeline
62
Acknowledgements
We would like to thank the following individuals
for their support

• Dr. Pat Donohoe
• Martin Jue, MFJ Enterprises
• Aimee Imparato

63
Questions?
64
References

• I. Hickman, Analog Electronics Analog Circuitry
  Explained, CRC Press, Inc., Boca Raton, Florida,
  USA, 1990. 
• H. L. Nattrass, Digital Measurement of FM
  Transmitter Quality, The Institution of
  Electrical Engineers, 1995.
• W. Lindsey and M. Simon, Phase-Locked Loop
  Their Application, IEEE Press 1977. 
• Blanchard, Phase-Locked Loops, John Wiley
  Sons, New York 1976.
• T. Wheeler, Electronic Communications for
  Technicians, Prentice Hall, Upper Saddle River,
  New Jersey, USA, 2001.

65
References

• A Vaisnys and E. Y. Chen, Digital Audio
  Applications to Short Wave Broadcasting, IEEE
  Catalog Number 97TH8280, 1997.
• D. A. Neamen, Electronic Circuit Analysis and
  Design, McGraw-Hill Companies, Inc., New York,
  New York, USA, 2001.
• C. K. Alexander and M. N. O. Sadiku, Fundamentals
  of Electric Circuits, McGraw-Hill Companies,
  Inc., New York, New York, USA, 2000.
• B. S. Hale, The ARRL Handbook for the Radio
  Amateur, American Radio Relay League, Newington,
  Connecticut, USA, 1988.
• M. N. O. Sadiku, Elements of Electromagnetics,
  Oxford University Press, Oxford, New York, 2001.