Using this electronic car porch guard system, you can prevent theft from occurring to your expensive vehicle. As soon as the system detects any potential attempt at theft, it promptly activates the porch light and gives off a piercing alarm. Before moving the vehicle out of the garage at night, a shrewd burglar will disable the security alarm that is installed in the vehicle before making any attempt to start the vehicle. Therefore, it would be incredibly challenging to discover who was responsible for the crime, and the loss wouldn't be noticed until the following morning. In order to foil any effort by the burglar, this circuit sounds an alarm whenever the vehicle is moved further away from the designated parking spot. The automobile porch guard's electrical circuit is depicted in Figure 1. A piezo element serves as the sensor for what is fundamentally an alarm that detects vibrations in the environment. When a voltage is put across the piezo element's terminals, the element's capacitance is normally in the range of a few tens of nanofarads, and it will quickly charge up as a result. The charge that is placed on the piezo element by the resistors R1 and R2 will remain on the element until it is shaken by some kind of mechanical motion. When the piezo element detects any vibrations, an alternating current voltage is generated across its terminals. This voltage is then amplified by the transistors T1 and T2 in the circuit. When transistor T2 starts conducting, capacitor C1 starts charging, and a voltage is delivered to the inverting input of integrated circuit LM311 (pin 3). (IC1).

The pin connections of the IC LM311's voltage comparator are distinct from those of other typical op-amps due to the fact that it is not a standard op-amp. In order to maximize the device's versatility, the output stage has both positive (pin 7) and negative (pin 1) outputs. Typically, the negative output is connected to ground. An npn transistor may be found at the output, and its collector is located at pin 7, while its emitter is located at pin 1. Therefore, the integrated circuit will act as a current sink while the output transistor is conducting. Circuit operation LED1 illuminates after being triggered by IC1 utilizing the emitter voltage of T2, which causes its output to sink through the resistance R4. VR1, which is part of a divider setup, is the component that supplies IC1 with its reference voltage. The monostable is triggered by a transition from high to low at the output of IC1, which goes from high to low (IC2). The values of R7 and C5 determine how long the output of IC2 remains high, and it is around three minutes. For the purpose of preventing spurious triggering at the reset pin of IC2, the time-delay components resistor R6 and capacitor C3 are used. The output of IC2 is connected to the triac BT136 and the alarm tone generator IC3 so that they can be triggered. By connecting the light's MT2 and MT1 terminals, the triac finishes the circuit that the lamp is part of. The value of resistor R10 determines the frequency of the oscillations produced by IC3's internal oscillator. In order to create a police siren, pin 6 of IC3 must be connected to pin 5 of Vcc. Transistor T3 acts as an amplifier for the signal that is produced by IC3. The piezosensor is an inexpensive and easily accessible buzzer that does not have an oscillator. Install it on one end of a PVC pipe that is two meters long. The other end should be sealed off with a cap so that the pipe can perform the function of a resonator and boost the piezosensor's sensitivity. Connect the piezosensor to the circuit by hiding the single-core shielded wire that you use to connect it using the appropriate amount of discretion.

After the circuit has been assembled on a PCB designed for general use, place everything but the piezo sensor inside of an appropriate cabinet. Using nuts and bolts,

secure the PVC pipe with the sensor to a wooden plank that is two meters long and fifteen centimeters broad. In order to keep the PVC pipe buried beneath the surface of the floor, the wooden plank needs to be fastened across the entrance to the automobile porch.