Building an FM Transmitter Circuit for Car Stereo is easy way to play music from phone, MP3 or Bluetooth on car FM radio.
It sends sound on FM frequency and car radio catches it like normal station.
Circuit is simple to use and is good for playing music or podcast in car without special stereo system.
Circuit Working:
Part List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | 100k 1/4 watt | 1 |
| 330Ω 1/4 watt | 1 | |
| 470k 1/4 watt | 2 | |
| Capacitors | Trimmer 50pF | 1 |
| Ceramic 5pF | 1 | |
| Ceramic 0.1μF | 1 | |
| Ceramic 0.001μF | 2 | |
| Semiconductors | Transistor 2N2222 | 1 |
| Coil 8 turns of 20 SWG insulated copper wire on a 5mm diameter plastic former | 1 | |
| Antenna use a 28SWG, 10cm long insulated copper wire for the antenna. | 1 | |
| Battery 3V | 1 |
Making FM transmitter for car stereo is like building simple FM circuit.
It uses small 3V battery to power parts like oscillator, modulator and amplifier.
Audio from stereo goes through R3, R4 and C4 and then these mix left and right sound and send to modulation part.
R3 and R4 work as voltage dividers, C4 blocks DC and lets only audio pass.
Transistor Q1 is heart of oscillator.
LC tank with coil L1 and capacitor C1 makes high frequency wave like carrier.
Audio changes this waves frequency modulation.
C4 sends audio to Q1 base and keeps modulation clean without messing transistor bias.
Q1 makes the signal stronger for better transmission.
Signal goes out through antenna on Q1s collector.
Antenna length can change to send signal farther.
C3, C5 and R1 keep circuit stable which stop extra noise or unwanted signals.
Formulas with Calculations:
FM Transmitter Circuit Formulas & Easy Calculations:
1. Frequency of Oscillation:
Formula:
f = 1 / (2 * π * √(L * C))
where:
- f is the frequency in Hz
- L is the coil inductance in henries
- C is the capacitance in farads
Example:
L = 0.2 µH = 0.2 × 10⁻⁶ H
C = 50 pF = 50 × 10⁻¹² F
Then:
f = 1 / (2 × 3.1416 × √(0.2 × 10⁻⁶ × 50 × 10⁻¹²))
f = 159 MHz
To change frequency fit in 88 to 108 MHz FM band and adjust trimmer capacitor C1.
2. Transistor Q1 Biasing:
Formula:
Vb = Ib × R2
where,
- Vb is the voltage at base
- Ib is the base current
- R2 is the 330Ω used in circuit
R2 helps to bias transistor properly.
3. Capacitor Impedance (Z):
Formula:
Z = 1 / (2 * π * f * C)
where:
- Z is the impedance in ohms
- f is the frequency in Hz
- C is the capacitance in farads
Example:
C4 = 0.1 µF = 0.1 × 10⁻⁶ F
f = 1 kHz
Then:
Z = 1 / (2 × 3.1416 × 1000 × 0.1 × 10⁻⁶)
Z = 1590Ω
This help us design and tune FM circuit for car stereo use.
How to Build:
For Building an FM Transmitter Circuit for Car Stereo follow the steps mentioned below:
- Gather all parts from circuit diagram.
- Connect collector of Q1 to one side of L1 coil and other side of L1 connect to +3V.
- Connect emitter of Q1 to GND through R2.
- Connect base of Q1 to one side of C4 and other side of C4 to R3.
- One end of R3 goes to audio left and GND.
- R4 is in parallel to R3 which goes to audio right and GND.
- Put C1 between collector of Q1 and L1.
- Connect C2 between emitter of Q1 and C1.
- Connect antenna between C1 and C2.
- Add C5 from +3V to GND.
Conclusion:
Building an FM Transmitter Circuit for Car Stereo is easy and is low-cost way to play audio from phone or device to car radio.
It sends sound over FM signal and car radio picks it up.
It is an fun and simple project for beginners and DIY lovers.
Just choose right frequency and avoid interference for best result.