This circuit can prevent a car theft. By the delaying them, not to steal our cars easily. Which can use in both cars and motorcycles, that uses a battery 12 volts and also cheaper too.
The working principle.
In Figure 1 is the Car burglar system with start delay. When we apply a voltage supply on first time, the capacitor C2-22uF will delay time the circuit not work immediately. Then C2 is discharged with a resistors R2-50K.
Figure 1 The complete circuit of Car Burglar system with start delay
Once through this period. The circuit will checking a undulation of voltage. By have a potentiometer VR1-100K is adjusted a sensitivity. When the car starts to cause ripple voltage. The undulate will be the C1 coupling a signal go to pin 13 of IC1/1, by passed way the VR1 and R4
IC1/1(LM324) is used to amplify the voltage out away pin 14 through R6 into pin 3 of IC1/2, so causes pin 1 of IC1/2 has high voltage. And is send trough R8, D2 (1N4148) into pin 3 so that pin 1 of IC1/2 has high voltage all time. The LED1 will glow to indicate to khow that the circuit ready.
The capacitor C4(47uF) will Be recharged through D3, R10.By takes about 10 seconds. So causes pin 8 has high volts send through R15 into pin B of Q1(C945) to drive relay works.
When the contacts of the relay tap for 10 second, LED will go out. Now if we connect it to the alarm circuit is noisy. The Q1 is pull the voltage at pin 9 through D5, R13, so cause pin 9 of IC1/3 has a lower voltage.
The C4 will be out of the R9 discharge for about 1 minute. The voltage at C4 is connected to pin 10 of IC 1/3 lower than pin 9, Makes pin 8 no voltage out. The Q1 stopped working at the same time. The relay contacts. They IC1 / 4, R16 and C5 to Stop detection. After the relay contacts. To prevent a repeat performance. The circuit will be checked again. The relay contacts are released, about 5 seconds.