FM transmitter for smartphone MP3 Player 2N2218 LM741

FM transmitter for smartphone MP3 Player 2N2218 LM741

Circuit diagram, FM transmitter for smartphone MP3 Player 2N2218 LM741. Evolution FM transmitter with 2n2218 with audio amplification step using LM741 op amp with audio input for MP3, MP4, mobile, computer and other audio sources, beyond the traditional electret microphone. With great sensitivity to the input signal. Using fewer components and easy assembly makes it ideal for those who want even without much experience assembling an FM transmitter with reasonable power.

About the FM transmitter circuit

Circuit based on another project with transmitter 2n2218, posted on the blog.
Power supply be 6 to 12V Battery or  good quality power supply, is recommended during test and adjust use of 9 or 12V battery.
The coil should be obtained four winding turns of enameled wire 22 AWG air core self-sustained and 1 cm diameter. Also in this case we connect the antenna between the third and fourth loop because it ensures greater stability in the transmission.
The variable capacitor should be with maximum capacitance 30-50 pF.
If you prefer, you can use an adjustable coil of this FM receiver and put a fixed capacitor of 4.7pF instead of CV.
The antenna can be a telescopic 80 cm, a piece of stiff wire or a specific antenna for FM transmitter. Must be connected at the point marked by Ant, and the coil is connected via C2.
As the circuit has an audio input type P2 to be connected to many audio source, we adopted a trimpot to adjust the signal level of the circuit. Also adopted was a key to disable the electret microphone.

Use a heat sink in the transistor, which may be a commercial or DIY  piece of aluminum

To-39 Heatsink Use A Heat Sink In The Transistor, Which May Be A Commercial Or Diy Piece Of Aluminum

Schematic circuit diagram FM transmitter for smartphone MP3 Player 2N2218 LM741

Circuit Diagram Transmitter For Smartphone Mp3 Player 2N2218 Lm741

Suggested printed circuit board PCB for assembly of the FM transmitter

Pcb Circuit Diagram Transmitter For Smartphone Mp3 Player 2N2218 Lm741
Pcb Component View Circuit Diagram Transmitter For Smartphone Mp3 Player 2N2218 Lm741
Pcb Component Silk Circuit Diagram Transmitter For Smartphone Mp3 Player 2N2218 Lm741

BOM for assembly FM transmitter with 2n2218

Part Value
Resistors 1/4 Watt 5%
R1 4.7k — Yellow, Violet, Red, Gold
R2 8.2K — Gray, Red, Red, Gold
R3, R6 47k — Yellow, Violet, Orange, Gold
R4 (If the gain is too high, decrease the value of this resistor) 33k — Orange, Orange, Orange, Gold
R5 1K — Brown, Black, Red, Gold
R7 6.8K — Blue, Gray, Red, Gold
R8 47 — Yellow, Violet, Black, Gold
R9, R10 10K — Brown, Black, Orange, Gold
C1, C6, C9 100nF — (104) Ceramic Capacitor
C2 10pF (10p) — Ceramic Capacitor
C3, C7 10nF (103) — Ceramic Capacitor
C4 100nF a 1µF  — Film or ceramic capacitor
C5, C11, C12 10µF/16V — Electrolytic Capacitor
C8 100µF/16V — Electrolytic Capacitor
C10 4.7p (4p7 or 4.7p) — Ceramic Capacitor
CV 3-30pF – Ceramic Trimmer
IC1 LM741P — Operational amplifier integrated circuit.
Q1 2N2218, 2N2219, 2n2218a or 2n2219a, or equivalent – NPN transistor
J1 (IN) P2 connector – Audio input
B Connector for connecting the battery from 6 to 9 Volts
ANT Point to connect the antenna
L Coil – See text.
MIC Electret microphone
P Trimpot de 10k — Potentiometer Trimmer
S1 Switch to activate the microphone
PCB, Battery, Case, Antenna, etc.

Download PDF files of this assembly – PCB, Copper side, Component side, Gerber files, Pads, Silk, Schematic, Datasheet, 2n2218, 2n2219, lm741.
Download PDF      Mirror

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About the author blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.

8 thoughts on “FM transmitter for smartphone MP3 Player 2N2218 LM741”

  1. toni este transmissor eu posso receber o audio da mesa de som para o fone de ouvido usando sem fio e vc já tem uma montada para mim vender


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