This article describes a simple and easy to choose four-tone audio switch circuit, which can choose one of the four sources as the output.
First, the working principle circuit
It consists of 4-wire-10-line coder CD4028, A, B, C, D are code input terminals, and Qo~Q9 are decimal decoding outputs.
The circuit is shown in the figure. When the switch SB is pressed, the circuit is energized. S1, S2, S3, and s4 are four tact switches. When S1 is pressed, the input of D, C, B, and A inputs is BCD code 0001. At this time, only ten outputs are Q1 output high. Flat, the LED 2 is lit, indicating that the input signal is gated. At the same time, the triode VT1 is turned on, and the first audio signal source flows through the c and e poles of VT1, and is output from the “output†end. When Sl is released, the contact of switch S1 trips. At this time, due to the resistance R2, the high level of the output terminal Q1 is fed back to the input terminal A, so that Ql is automatically kept at the high level output. When S2 is pressed, the input corresponding to D, C, B, and A is BCD code 0010. At this time, only ten outputs of Q output are high level, and LED LED1 is lit, indicating that the input signal is strobed.
At the same time, the triode VT2 is turned on, and the second audio signal source flows through the c and e poles of the VT2 and is output from the "output" terminal. When S2 is released, the same reason, Q2 can automatically keep the high level output unchanged.
At this time, Ql outputs a low level, LED2 goes out, and the first audio signal source is turned off. When S3 is pressed, the input corresponding to D, C, B, and A is BCD code 0100, and the third audio signal source is strobed. When S4 is pressed, the input corresponding to D, C, B, and A is BCD code 1000. At this time, the fourth audio signal source is strobed, thereby realizing four choices for the audio input signal.
Second, component selection
The parameters are all shown in the figure, wherein LED1-LED4 is a red LED, S1~s4 are tact switches, and SB is a toggle switch.
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