FM transmitter for smartphone MP3 Player 2N2218 LM741
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 1cm 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 80cm, 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 in many different 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 of micro FM transmitter with 2n2218

FM transmitter 2N2218 schematic
FM transmitter 2N2218 schematic

Suggested printed circuit board for assembly of transmitter

FM transmitter 2N2218 PCB
FM transmitter 2N2218 PCB layout
FM transmitter 2N2218 PCB silk

Part List for assembly FM transmitter with 2n2218

PartsValue
Resistor’s 1/4 Watt 5%
R14.7k – Yellow, Purple, Red, Gold
R28.2K – Grey, Red, Red Gold
R3, R647k – Yellow, Purple, Orange, Gold
R4220k – Red, Red, Yellow, Gold
R51K – Brown, Black, Red, Gold
R76.8K – Blue, Grey, Red, Gold
R847 – Yellow, Violet, Black, Gold
R9, R1010K – Brown, Black, Orange, Gold
Capacitor
C1, C9100nF – (104, .1, 0.1, or 100n) Ceramic capacitor
C210pF (10p) – Ceramic capacitor
C3, C710nF (103, 0.01, 10n)- Ceramic capacitor
C41µF/16V – Electrolytic Capacitor
C5, C11, C1210µF/16V – Electrolytic Capacitor
C61nF (102, 1n)- Ceramic capacitor
C8100µF/16V – Electrolytic Capacitor
C104.7p (4p7, 4.7p)- Ceramic capacitor
CV3-30pF -Trimmer
Semiconductors
IC1LM741P – Integrated circuit operational amplifier.
Q12N2218, 2N2219 or equivalent NPN Transistor
Connectors
INConnector P2 – Audio Input
BConnector for connecting the battery 6-12 Volts
ANTPoint to connect the antenna
Several
LCoil – See text.
MICElectret microphone
PTrimpot 10k
S1Switch for activate the microphone
PCB, Battery, Box, etc..

If you like assemblies transmitters see other related articles.
Download PDF files of this assembly – PCB, side copper, side components, pads, Silk, schema, Datasheet, 2n2218, 2n2219, LM741.
Download PDF      Mirror

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5 COMMENTS

  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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