Car anti-theft alarm circuit (2)

This simple car anti-theft alarm circuit has the characteristics of using few components and being easy to make.
  (1) Circuit composition The car anti-theft alarm circuit consists of the time base circuit NE555, high-power switch tube VT, switch S2, delay capacitor C
and resistor scale, ~ wind, etc., as shown in Figure 13-34.
    Sl (Sla, Slb) is the car ignition switch (lock
switch). GB is the car battery, and Re is
the additional current-limiting resistor used in the car to match the ignition coil.
    (2) Circuit working principle When the car starts and runs normally
, switch S2 is placed at point b, and the anti-theft circuit does not work.
    While the car is parked, place S2 at point a. If
Sl is turned on at this time, the +12V voltage will charge C through Ri, causing the potential of pins ② and ⑥ of the IC
to gradually increase, and at the same time, pin ③ of IC
will output high level, the VT is turned on, the ignition circuit is connected, and the engine
can be started. After a few seconds of delay. c After charging,
when the potential of IC’s ② and ⑥ pins rises to 8V, the flip-flop inside the IC
flips, and its ③ pin changes from high level to low level, VT is cut off,
the ignition circuit is disconnected, and the engine automatically shuts down. The car cannot
be driven away. The sound of the engine starting and stopping repeatedly is equivalent to an alarm signal.