Play a sound for a fixed duration when a button is pressed - a poor man's door bell!
This is a build of a simple "door bell" circuit published by Circuitstoday.
It operates by using one 555 timer in monostable to trigger an astable signal on a second 555 for a defined period.
The duration of the "chime" is determined by the values of R4 and C1 which set the monostable high cycle for the first 55 timer. With 10kΩ and 33μF this is about 363ms.
When the output of the first 555 goes high (pin 3), this pulls the reset pin 4 high on the second 555.
The astable signal of the second 555 is governed by R3, R5 and C3. With R3=1kΩ, R5=22kΩ and C3=100nF this runs at about 320Hz with a 51% duty cycle. The schematic indicates using variable resistor for R5, but this can be replaced with a resistor if a fixed frequency is acceptable.
- LM555 Datasheet
- Visual 555 Calculator
- Door bell circuit using NE555 - original circuit from Circuitstoday