MP3 transponder, MP3 Transmitter
Keywords: MP3 forwarder
The MP3 forwarder can forward the MP3 player's music or songs to the car's audio system for play, so that you can enjoy the high-fiscal music with high fidelity in driving travel, and can share with the same car, both of the MP3 play The function of the device (personal listening to expansion is listening at the same time), and also adds the source of the car audio system (MP3 can download and update your favorite songs at any time), it is worth a car trial.
A circuit working principle The MP3 forwarder is actually a FM stereo repeater using a car 12V DC power supply, which transmits the stereo audio signal output by the MP3 player with a frequency modulation method, and the existing FM radio is received. Playback. The biggest convenience does not require any changes to the original audio circuit of the car. As shown in Figure 1, the MP3 forwarder circuit is shown in the circuit, and the circuit BA1404 (IC1), the circuit is simple, the peripheral component is small, the sound quality is high, and the stereo separation is simple, and the work is reliable.
The BA1404 is a single-chip integrated circuit designed for the FM stereo transmitter. The 18-pin double-column inserted package, the internal circuit structure is shown in Figure 2, which contains a stereo amplifier, a balanced modulator, a 38kHz oscillator, a radio frequency oscillator Unit circuits such as radio frequency amplifiers, connecting a small amount of peripheral components to form a complete stereo modulation and transmit circuitry, and the transmit frequency is determined by an external LC circuit by an external LC loop within 88 to 108 MHz frequency modulation.
Left, right channel audio signals are input from 18 feet, 1 pin, respectively, by internal L, R amplifiers, respectively, enters the balanced modulator, and the modulated stereo signal is output from 14 pin. R1, C1 (R2, C2) constitutes an input of the time constant of 50 USS, to match the frequency characteristics of the FM radio. C3, C4 is an input coupling capacitor. RP1 is a balanced adjustment potentiometer. The 38kHz oscillator requires an external 38kHz crystal, and the oscillation signal is buffered by buffering and 1/2 divided by 13 pins. R3, C7, R4, and C8 constitute a mixed network, mix the pilot signal output from the 14 pin to the 13 pin as a composite signal, and then enter the IC1 by 12 pins to adjust the RF signal. L1, C10, C11, C12 form a radio frequency oscillator through 10 pins and 9 pins, and the oscillation frequency depends on L1, C10, about 92 MHz. After the radio frequency signal modulated by the composite signal is amplified by the internal radio frequency amplifier, the 7 pin is output, and the C16 is coupled to the antenna W emits out. The integrated circuit BA1404 supply voltage allows for a range of 1.0V to 2.5V, and the 12V power supply of the automobile must be used as a working power supply. In the circuit diagram of Figure 1, the operating voltage of the design BA1404 is 2V, R5 is a buck resistor, and Vd1 is a regulator tube, which is used as a light-emitting diode as a stasible pipe. LED pressure drop is generally 2V, with certain regulatic characteristics, while also serving as a working indicator, two from one fell swoop. C17, C18 is a power filter capacitor.
Two production, debugging and use component parameters are shown in Figure 1. In addition to the electrolytic capacitance, the remaining capacitance should be used in high frequency porcelain interversion. RP1 uses a linear fine tuning potentiometer. VD1 is a light emitting diode, which can be used with your favorite color. Since the VD1 also serves as a regulated pipe, the positive tube pressure drop of the selected light emitting diode must be between 1.5V to 2V. The inductance needs to be self-made, L1 is a hollow coil, and the lacquer line of 0.5 mm in diameter is 4 turns around 4 turns on a round rod (for example, a ballpoint pen heart), remove the coil from the round rod to 6 mm. L2 uses 100KΩ resistor to make a skeleton, with a diameter of 0.1 mm enameled wire around 80 turns, and the two tiers of the coil are welded together with the resistance two-to-foot. The audio signal input terminal uses a 3.5mm stereo socket. The antenna W uses a 20cm long wire generation. 12V Power input Connect a car cigarette lighter plug. The whole machine is installed in a small plastic box. Debug includes two items: 1 Adjust the transmit frequency. Turn on the MP3 forwarder power supply, the input is accessed into the audio signal, and then the frequency modulation signal emitted by the forwarder radio receiver should be received near 92MHz. If the signal is not received, it can be used to change L1 by the insulator to change its turn. The increase of the turret can increase the emission frequency, and the reduction of the turret can reduce the transmit frequency until the FM radio receives the signal of the repeater. The frequency of avoiding the local FM radio station during the adjustment process. 2 Adjust the channel balance. Adjust the RP1 to match the left and right channel signals. A audio cable should be homemade to facilitate the connection of the MP3 player and the repeater. The method is to connect two three-dimensional stereo plugs with two diameters, as shown in FIG. The shield is connected to the public end of the two plugs and cannot be mistaken.
The connection method when used is shown in Figure 4. One end of the homemade cable is inserted into the headphone jack of the MP3 player, and the other end is inserted into the audio input socket of the transponder. The power plug of the repeater is inserted into the car cigarette lighter, and the power indicator VD1 should be bright. Turn on the MP3 player, use the car fuel radio to search for stereo signals that receive MP3 playback. If the body shield causing the receipt, the transponder antenna can be moved to the window glass, or the inner antenna is installed for the FM radio on the car.
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