The car's audio system has only two functions, radio and tape player. Can you play MP3 music with the existing audio system? The author studied this car audio circuit and found that its function adjustment is controlled by bus. The model number of the signal selection IC is TDA7313, as shown in the middle figure. The left channel signal passes through the (13), (14), and (15) pins, and the right channel is switched through the (9), (10), and (11) pin input integrated circuits. The radio signal is passed through the (11) and (15) feet, and the tape player is input through the (10) and (14) pins. Although there are still two inputs left unused. But the circuit is controlled by the bus, and it is impossible to change the software. Only think of ways to change the hardware. After analysis. It is easier to change the radio part. First, the Cl and C6 in the middle figure are welded and welded to the positions C6 and C7 in the above figure. The (1) and (5) pins of the signal terminal CN are connected to the negative poles of the original Cl and C2 positions in the middle of the middle, and the (3) and (4) feet are respectively connected to the positive poles of the original C1 and C2 positions of the middle map. On the top, (2) and (6) are connected to a signal input socket as the MP3 source input. The signal input socket and the signal switching key AN are respectively mounted at appropriate positions on the audio control panel. The +KV power supply in the above figure is connected to the (2) pin of the TDA7313, and the +12V is connected to the input power of the audio system. The modified line is shown below. In order to ensure that the audio signal is not distorted, a small relay is used here to switch the signal. After the author's design and continuous improvement, the circuit shown in the figure is finally formed.
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The switching circuit consists of two integrated circuits, ICl (NE555) and IC2 (CD4013). The ICl and peripheral components form a monostable flip-flop, and the IC2 and peripheral components form a bistable circuit. The control principle is introduced as follows: When the audio system power is turned on, the +KV terminal inputs 5V power, and the voltage across C1 cannot be changed. ICl output is high.
Turn IC2 over, VT turn on, relay pulls in, and the signal switches to the signal input socket, which is not allowed. Then connect R2 and IC3 on the (4) pin of ICl to form a power-on reset circuit. The reset time T1 is made larger than the charging time TO of Cl. In addition, a capacitor is connected to the negative pole of the (11) pin of IC2, thus ensuring the accuracy of the control, and changing the previous state at the time of booting. Use MP3 as the audio input, after inserting the MP3, press the touch button. AN, ICl's (2) pin voltage is 0, less than 1/3VCC, (3) pin output high level, IC2 flip output high level, VT is on, relay K is closed, contact is switched to signal input socket At this time, you can enjoy MP3 music. After the button AN is released, the power supply is charged to Cl through R1. When the voltage is higher than 2/3Vcc, the output is low, waiting for the next button. When we want to listen to the radio, just press AN again, ICl outputs a high level, and IC2 flips the output low. Relay K loses power, the normally closed contact closes, and the radio signal path is turned on.
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