Using NE555 to make an audio signal generator

This circuit can be used as an audio signal source for the inspection and measurement of various audio circuits. When the power is turned on, the 555 starts audio oscillation and outputs through the C2 capacitor coupling. The oscillation process is: first, C1 is charged through R1 and R2. When the voltage on C1 reaches about 2/3VCC, the 3rd pin of the 555 output terminal changes from a high level to a low level. Pins 7 and 1 are connected, and then C1 is discharged through R2. When the voltage on C1 drops to about 1/Vcc, the 7th pin of the 555 and pin 1 are cut off, and the output of pin 3 becomes a high level. As mentioned above, C1 repeatedly charges and discharges to form audio oscillation. The high level of the output oscillation signal is close to Vcc, and the low level is close to 0V. The oscillation frequency is approximately:

f=1.44／(R1+2R2)C1 According to the component values ​​in the figure, the oscillation frequency is about 580Hz.