Guest arrival signal recognition circuit

The electronic doorbell circuit consists of a short pulse recognition circuit, a long pulse recognition circuit and a music generation circuit, as shown in the figure. ,
    the following introduces an electronic doorbell with guest recognition function
. When the doorbell button is pressed using the conventional method, it will
play a piece of music;
when the doorbell button is pressed continuously by hand for a short period of time, it can make a "ding dong" sound three times. If family members and relatives
use the latter method of answering the bell, the owner can
determine whether the visitor is a family member, relative, friend or stranger through the sound of the doorbell
. Circuit working principle: The short pulse identification circuit is composed of the NOT gate Dl, the NOT gate D3, the resistor island, the capacitors CI, G and the diodes VDJ and VD2 inside the
    six-NOT
gate integrated circuit IC 1 .     The long pulse recognition circuit is composed of the NOT gates D4-D6, resistor, diode VD3 and capacitor C3 inside IC1.     The music generating circuit is composed of music integrated circuits IC2 and IC3, audio amplifier tubes VTI and VT2, and speaker BL. S is the doorbell button . Shu is the current limiting resistor.     When S is pressed as usual, the input terminals of the NOT gate Dl and the NOT gate D4 both become low level, and the output terminals both become high level.     Due to the DC blocking effect of c1, the high level at the output end of NOT gate D1 cannot cause the short pulse recognition circuit to operate, and IC2 does not work. The high level at the output terminal of NOT gate D4 charges capacitor C3 through resistor R3. When the voltage at both ends of C2 is higher than 1.SV, the NOT gate flips and its output terminal becomes low level , causing the output terminal of NOT gate D6 to become As a high level, IC3 is triggered to work and outputs a music signal. This signal is amplified by \rT2 and drives the speaker BL to play a piece of music.     When S is pressed continuously for a short period of time (about 3 or 4 times at least once per second), a continuous positive pulse signal will be generated at the output This pulse signal After being rectified by VD2, Cz is charged. When both ends of Cz are higher than VnD/2, the output terminal of non-nine D2 becomes low level, the output terminal of NOT gate D3 becomes high level, ICZ is triggered to work, and the output music signal. After this signal is amplified by VT1, a "ding dong" sound is emitted through the speaker BL. The positive pulse output by the NOT gate m cannot increase the voltage across C, so the long pulse identification circuit does not operate and cannot trigger IC 3 to work.