555 guest welcome and farewell electronic model circuit

Published:2011/6/7 8:26:00 Author:TaoXi | Keyword: 555, guest, welcome, farewell, electronic model | From:SeekIC

As the figure 15-35 shows, the electronic model is composed of two channels of generating circuit, each channel of circuit is composed of a photoelectric sensor, a 555 and a voice circuit. The photoelectric sensor uses the 3DU type photosensitive tube, when the guest comes in or goes out, guest's body interrupts the light which illuminates on the VT1(or VT3), so the photosensitive tube has the high resistance, the pin-2's electric potential of 555 is lower than the 1/3VDD trigger electrical level, so the IC1 (or IC2) sets to output the high electrical level, the IC3 is triggered to send out the voice of welcome . At the same time the VT2 conducts, the collector electrode's low electric potential adds to the pin-4 of IC2 to mandatory reset the 555 no matter whether the VT3 has illumination.



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