This is a design circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. This is the figure of the circuit;
The Holtek HT-2811 is available from Maplin electronics in the UK, order code BH69A. The operating voltage must remain within 2.4 to 3.3 Vdc and standby current is minimal. The reset switch zeroes the count, and the 7 segment display is a common cathode type. To save power consumption the display can be enabled or disabled with a switch as shown in the above diagram. The count will still be held in memory. The envelope of the chime is set by the 220k, 330k, 3u3 and 4u7 resistors and capacitors. These values are the manufactures default values, but may be adjusted to alter the length and delay of the chime. The combination of the 2k2, 22k and 47u resistor capacitor network has a double function. It provides a de-bouncing circuit for the bell press and at the same time has a sufficiently long time constant. This ensures that anyone rapidly pressing the doorbell switch, only advances the count once. The 47u capacitor may be increased in size, if needed.
The Holtek HT-2811 is available from Maplin electronics in the UK, order code BH69A. The operating voltage must remain within 2.4 to 3.3 Vdc and standby current is minimal. The reset switch zeroes the count, and the 7 segment display is a common cathode type. To save power consumption the display can be enabled or disabled with a switch as shown in the above diagram. The count will still be held in memory. The envelope of the chime is set by the 220k, 330k, 3u3 and 4u7 resistors and capacitors. These values are the manufactures default values, but may be adjusted to alter the length and delay of the chime. The combination of the 2k2, 22k and 47u resistor capacitor network has a double function. It provides a de-bouncing circuit for the bell press and at the same time has a sufficiently long time constant. This ensures that anyone rapidly pressing the doorbell switch, only advances the count once. The 47u capacitor may be increased in size, if needed.
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