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555 synchronization/quasi-synchronization video-audio switch

2016-09-11 18:44  
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555 synchronization/quasi-synchronization video-audio switching circuit
As the figure 14-19 shows, this circuit is composed of the improved R-S bistable trigger circuit (composed of the 555) and the four-analog switch CD4066. This circuit has the function of synchronous switching and quasi-synchronous switching. The NAND gate is composed of the VT1 and VT2, the OR gate is composed of the VT3 and VT4, they control the IC1(555)'s trigger port (pin-2) and the reset port (pin-4) respectively, VT6 is the set lock circuit. The connection method of this circuit makes the video input I and the audio input I to be the priority channel, that is why the VT1 and VT4 are in the cut-off state. When you need to input I, you should press AN1, the VT2 conducts, the pin-2 of 555 has the low electrical level to lock the set state.