With this circuit you will be able to mount a mini stereo FM station and broadcast to your entire home, a simple way to have an audio link wireless with ease. With the FM transmitter BA1404 Hifi Stereo you can stream your music from your iPod MP3, satellite receiver, computer, DVD player, Mobile Phone, MP4 player and MP3 and other audio source directly to an FM receiver with crystal clear sound.
Schematic of the FM stereo transmitter BA1404
This is the diagram of the transmitter, the connectors CN1 and CN2 are stereo audio inputs of the trimpot (pots can be added) are for the volume adjustment capacitor + resistor (R1 / C4 and C11 / R2) form the pre-emphasis filter in the case of Brazil is 75μS.
The crystal ensures 38KHz stereo broadcast, in case you do not find this component to the assembly of your circuit, you will have a mono high-quality transmission, the MPX signal (with 2 audio channels multiplexed), leave the pin 14 and join with the 19kHz pilot signal (pin 13) and return to ci on pin 12 and will take the stage high-frequency oscillator formed on pins 9 and 10, the coil of 3.5 turns of the type found in FM radios in parallel with the 10pF capacitor C13 will be responsible for the fluctuation in the FM band.
The following high-frequency signal of the transistor T1 pin 7 to ensure a greater distance n transmission, the antenna coupling capacitor C9 which may be a telescopic or a piece of stiff wire.
The power supply should be a battery 9Volts preferably rechargeable 9-volt feed to the power transistor, as BA for the integrated circuit 1404 is required only 3 volts or it can burn. then 3 1N4148 diodes are used as a reference voltage of 2.1 volts in this source.
When assembling this circuit, make sure all components are positioned in the correct place and then connect the battery, then connect an audio source such as an MP4 and a nearby FM receiver, adjust the coil, using a “little key “plastic or wood, until you hear the signal on the radio. If you can not try to set other values for C13, and without then redo the settings.
Suggested PCB mounting stereo FM transmitter with integrated BA 1404 and crystal 38KHZ
List of material for assembly of the FM transmitter with BA1404
|Resistors 1/8 Watt 5%|
|R1, R2||47K – Yellow, Violet, Orange, Gold|
|R3, R7||270 – Red, Violet, Brown, Gold|
|R4||10K – Brown, Black, Orange, Gold|
|R5||4.7K – Yellow, Violet, Red, Gold|
|R6||150K – Brown, Green, Yellow, Gold|
|R8, R9||22K – Red, Red, Orange, Gold|
|R10||470 – Yellow, Violet, Brown, Gold|
|C1, C5, C10, C12||10µF/16V – Polarized Electrolytic Capacitor|
|C2,C4, C7, C9, C11, C15, C17||1nF – 25V Ceramic Capacitor|
|C3, C6, C8, C13, C14||10pF – 25V Ceramic Capacitor|
|C16||470µF/16V – Polarized Electrolytic Capacitor|
|IC1||BA1404 – FM stereo transmitter chip|
|T1||2SC2458 – RF Transistor|
|D1, D2, D3||1N4148 – Diode|
|L1||3.5 turns coil with adjustable core|
|P1, P2||1k – Trimpot – Volume Adjustment|
|ANT||Connect telescopic antenna or piece of stiff wire|
|CN1||Left audio connector|
|CN2||Right audio connector|
|X1||38KHz quartz crystal|
|Solder, wire, printed circuit board, box, connectors, etc..|
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About the Author: Xtronic.org blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.