Disconnection alarm

The figure below is a common multivibrator connection method. The timing resistors R1 and R2 are connected to the DIS terminal ( pin 7) of the 555. C l is the timing capacitor. When the power supply voltage Vee is applied to the circuit , the power supply charges Cl through Rl and R2 . When the voltage on C l (pin 2 ) rises to two-thirds of Vee , the internal flip-flop is reset and the output ( pin 3) flips to low level. DJ. Quantuan   (  pin 7) is internally conductive, and C l is discharged through R2 . When the voltage on Cl drops to one-third of Vee , the internal flip-flop is set, the output ( pin 3) flips to high level again, DIS is internally cut off, one cycle ends, and a new cycle begins.

Using this principle, we can make 555 into a disconnection alarm, and when s2 is disconnected, 555 will produce a vibration of about 3kHZ , causing the buzzer to make a harsh sound to achieve the purpose of alarming.