iPod FM Transmitter
Created by:
Larissa Duron
David Orozco
FM Transmitter - Purpose
Created to stream music from your iPod
using an FM stereo in your car or at home.
The sound from the iPod will broadcast
through the transmitter and play through an
FM frequency.
FM Transmitter & iPod
A FM Transmitter is portable device that uses
FM radio waves to send sound from any
audio device that contains an auxiliary port or
mini jack.
The iPod is a portable media player that
plays several audio formats using a flash
memory, a touch screen with video
capabilities.
FM Transmitter & iPod
FM – Frequency Modulation
The carrier’s amplitude stays constant and its
frequency varies according to the amplitude
variations of the audio signal.
When the input signal’s amplitude increases
the frequency of the carrier increases too.
FM – Frequency Modulation
When the input signal decreases in amplitude
the carrier frequency decreases.
The output frequency the transmitter is
adjustable from 88 to 108 MHz which is the
FM band that is used for radio broadcasting.
FM - Testing
For testing purposes, the circuit was
designed in Multisim to assure working
ability.
The input frequency (iPod) was defaulted to
100 MHz.
FM – Testing Multisim
In this figure, you can see that the frequency range is at 116.83 MHz which
indicates that the circuit works. Adjustments will be made after the
calculations for accurate FM broadcasting.
Components
iPod
Analog Auxiliary cable (male to male)
¼ copper wire (antenna)
LED
Capacitors: Resistors: Transistor:
C1, C2 = 0.01uF R1 = 27 K ohms Q1 = BC337
C3 = 10PF R2 = 10 K ohms
C4 = 1uF R3 = 470 ohms Vin = 9V
C5 – 0.33uF R4, R5 = 1 K ohms
C6 = 0.1uF R6 = 150 ohms
C7 = 100pF (Variable)
IC Regulator = 7806
Components
Purpose of the components
Capacitors - to protect the circuit by storing
energy in the electrostatic field.
Voltage regulator - to maintain a constant
output from a voltage source even when the
load current varies.
**The voltage regulator is keeping the voltage
constant at 6 volts – 5 volts in Multisim**
Purpose of the components
RF coil - acts as an inductor and stores the energy in a
magnetic field and creates a carrier frequency to the
variable capacitor.
Variable capacitor - changes the energy from 5% to
100% and works with the RF coil to create a carrier.
Resistors - provide a given opposition to the current
flow which is also needed for protection to the current
flow.
Schematic V2 123
XFC1
5V
0
C3 R3
8
C7
10pF 470 Ω
XMM1 10 5% 100pF-VAR 0
Key = A
0 Q1
BC337
0 L2
SAMPLE_RFCOIL
U2
LM7805CT R1
VREG LINE
4 5
VOLTAGE
COMMON
27k Ω
1
R6 C4
150 Ω 1uF
V1 C5 C6 C2 3 C1
0.33uF 0.1uF 0.01uF 0.01uF R2
9V 0 10k Ω 7
LED1
0 0 0 0 0 0 R4 R5
0
1k Ω 1k Ω
XFG1
0 12
In this figure, 100 MHz frequency was used as the input frequency (iPod).
Calculations for RF coil (Inductance)
5
A = Avgdiameter = = 2.5mm
2
N = NumberTurns = 4
B = LengthCoil = .8mm
C = Diameter = 5mm
0.8( NA) 2 0.8(4 ⋅ 2.5mm) 2
induc tan ce = µH = = = 5.3µH
6 A + 9 B + 10C 6(2.5mm) + 9(0.8mm) + 10(5mm)
1 1
f R ( MIN ) = = = 36.2 MHz
2π L ⋅ C 2π 5.3µH ⋅ 100 −12
1 1
f R ( MAX ) = = = 143.5MHz
2π L ⋅ C 2π 5.3µH ⋅ 10 −12
Calculations with Inductors replacing the
RF Coil
Use two 8.2 µH inductors in parallel
1 1
L= + = 4.1µH
8.2 µH 8.2µH
1 1
f R ( MIN ) = = = 78.6MHz
2π L ⋅ C 2π 4.1µH ⋅ 100 −12
1 1
f R ( MAX ) = = = 248.5MHz
2π L ⋅ C 2π 4.1µH ⋅ 10 −12
Calculations for Antenna
λ = wavelength
f = 100MHz
c = 300,000,000
300,000,000 3 × 10
8
f = →λ = = 3m
λ 100 MHz
1
Lantenna = λ × Lantenna = 3m × = 0.75m
4
Testing Frequency - Oscilloscope
Conclusion
Music was transmitted from the iPod to the
antenna output source of the FM Transmitter
to a FM radio station – 90.1 FM.
Pros:
Inexpensive
Simplicity
Portable
Conclusion
