This circuit is built by CD4042 IC. The input of the design is result musical doorbell. CD4042B IC is popular IC to built up the voice of the bell. There are four data input that it will shown by LED (D1-D4). It will “on” if the main switch (S6) is turn on. The circuit figure is shown in below;
The principle work is when switch S6 is pushed to ‘on’ condition, the circuit gets +9V and the four data inputs (D1 through D4) of IC are in low state because these are tied to ground via resistors R1 through R4. Polarity input in pin 6 of CD4042B IC is also pulled down by resistor R5. Clock input (pin 5) of the quad D-latch is wired in normally low mode and hence all the four outputs (Q0 through Q3) have the same states as their corresponding data inputs. As a result, LED1 through LED4 are in off condition. There are four switches fitted at four different doors/gates outside the home and a monitoring panel in the common room of the home. If any switch is pressed by a visitor pins 2 and 4 of IC go high.
Simultaneously, pin 3 to IC (Q0 output) go low and LED1 starts glowing to indicate that switch S1 is pressed. Output in pin 13 of the dual 4-input NOR gate (IC2, here wired as a single 4-input OR gate) is high to forward bias buzzer driver transistor T1 via resistor R10. The final result is a soft and pleasing musical bell, which lasts until reset switch S5 is pressed by the owner. For this latching arrangement, output pin 13 of IC2 from the NOR gate is fed back to the clock input of IC1. The circuit costs around Rs 100.
The principle work is when switch S6 is pushed to ‘on’ condition, the circuit gets +9V and the four data inputs (D1 through D4) of IC are in low state because these are tied to ground via resistors R1 through R4. Polarity input in pin 6 of CD4042B IC is also pulled down by resistor R5. Clock input (pin 5) of the quad D-latch is wired in normally low mode and hence all the four outputs (Q0 through Q3) have the same states as their corresponding data inputs. As a result, LED1 through LED4 are in off condition. There are four switches fitted at four different doors/gates outside the home and a monitoring panel in the common room of the home. If any switch is pressed by a visitor pins 2 and 4 of IC go high.
Simultaneously, pin 3 to IC (Q0 output) go low and LED1 starts glowing to indicate that switch S1 is pressed. Output in pin 13 of the dual 4-input NOR gate (IC2, here wired as a single 4-input OR gate) is high to forward bias buzzer driver transistor T1 via resistor R10. The final result is a soft and pleasing musical bell, which lasts until reset switch S5 is pressed by the owner. For this latching arrangement, output pin 13 of IC2 from the NOR gate is fed back to the clock input of IC1. The circuit costs around Rs 100.
