Making telephone line burglar alarm based on rectifier tube

An oscillator is an electronic component used to generate a repeating electronic signal (usually a sine wave or a square wave). The circuit formed by it is called an oscillating circuit. It can convert direct current into an electronic circuit or device with a certain frequency of alternating current signal output. There are many types, according to the oscillation excitation mode can be divided into self-excited oscillator, other oscillator; according to the circuit structure can be divided into RC oscillator, inductor-capacitor oscillator, crystal oscillator, tuning fork oscillator, etc.; It is divided into sine wave, square wave, sawtooth wave and other oscillators. It is widely used in electronics industry, medical, scientific research and so on.
This alarm can monitor and prevent others from illegally stealing your telephone line. When someone is on your phone's outside line, the alarm will give an interference signal, so that the thief can't dial, and use the sound and light to remind the owner of theft. The following figure is the schematic diagram of the anti-theft device. Usually, the post office program machine sends a standby voltage of about 50V on the outer line. The upper side of the D1-D4 polarity is converted to the positive pole, and the D5 is broken through the R2 to increase the base potential of the T1. T1 is on, T2 is off, T3 is off, and the oscillation circuit consisting of T4 and T5 does not work. When the phone is stolen, the external line voltage drops to about 9V, D5 cannot be broken down, and T1 is cut off due to no bias. The base potential of T2 is increased and turned on. The conduction of T2 turns on T3 and drives the audio oscillation circuit of the latter stage. The LED and DY emit an audible and visual alarm, and the interference signal is added to the outer line through LED and DY. The voltage is pulled low, so that the pirate phone can't dial and forcibly hang up. Although the host lifts the voltage, it also reduces the voltage and makes T1 cut off, but because of T6 or T7 (T6 and T7 are used for easy installation, the incoming line can be divided. Polarity access, D6, D7 acts as an isolation) to obtain the base current through the telephone Pass, so that T3 can not turn on the oscillating circuit does not work. Therefore, the host can normally dial the call is not affected. Because only the R8 and R9 with small resistance are connected between the host phone and the outside line, the zero-zero call is not accepted when the call is received. influences.
Component selection: D1-D4, D6, D7 can be used with general rectifiers such as IN4007, D5 can use 18V regulator, DY is 3V electromagnetic buzzer. Resistor can use 1/8W carbon membrane resistor, other Component type