Password electronic doorbell 1

The password electronic doorbell circuit is composed of the electronic password circuit and music occurred circuit, and it is shown in Figure 3-118. Electronic password circuit consists of integrated circuits lCl and keys Sl-S6, diodes VDl-VD5. lCl is the electronic password IC, its pin 1-3 and pin 6 are the effective transmission input ends, and pin 7 is..

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