This is a circuit for tone generator. This circuit is once the switch to the 9V power supply is connected, the alarm will trigger at a frequency of approximately 1.27 kHz. It will remain ON for duration of approximately 170 seconds or 2.8 minutes before it stopped. This circuit is work with based on 555 IC. This is the figure of the circuit.
In this circuit, we used two 555 timers. U2 is configured as a timer in astable mode. Once triggered, it will emit a frequency from its output at pin 3 that will drive a Q1 transistor. Q1 transistor will turn ON and OFF according to the frequency of the circuit. It will in turn used to drive a 8 ohm loud speaker to emit a loud audible sound. The frequency of the sound can be adjusted by changing the values of R3= 47K, R4= 33K and capacitor C1=10nF. Change the values of these components and by using the formula for astable mode, the frequency of the sound can be obtained.
U1 circuit is used as a delay circuit which is configured as a mono stable mode. It is a one shot multivibrator that will generate a pulse at its output at pin 3 which will disable the astable circuit U1. In this circuit, pin 2 of U1 will go to logic 0 when the power supply is connected via the capacitor E1 and hence circuit U2 is immediately triggered.
In this circuit, we used two 555 timers. U2 is configured as a timer in astable mode. Once triggered, it will emit a frequency from its output at pin 3 that will drive a Q1 transistor. Q1 transistor will turn ON and OFF according to the frequency of the circuit. It will in turn used to drive a 8 ohm loud speaker to emit a loud audible sound. The frequency of the sound can be adjusted by changing the values of R3= 47K, R4= 33K and capacitor C1=10nF. Change the values of these components and by using the formula for astable mode, the frequency of the sound can be obtained.
U1 circuit is used as a delay circuit which is configured as a mono stable mode. It is a one shot multivibrator that will generate a pulse at its output at pin 3 which will disable the astable circuit U1. In this circuit, pin 2 of U1 will go to logic 0 when the power supply is connected via the capacitor E1 and hence circuit U2 is immediately triggered.
