This project demonstrates the design and simulation of an op-amp based alarm system using LTspice. The system detects input signals (simulating door/window sensors) and triggers an alarm using a comparator and transistor switching stage.

• The input signal is applied to the non-inverting terminal of the op-amp.
• A reference voltage is generated using a resistor divider network.
• The op-amp operates as a comparator.
• When the input voltage exceeds the reference voltage, the output switches HIGH.
• The output drives a PNP transistor, which acts as a switching device.
• The transistor activates the alarm (LED/load).

• Op-amp comparator operation
• Voltage divider for reference generation
• Transistor as a switching device
• Threshold-based detection

• Software: LTspice
• Input: Pulse signal
• Supply Voltage: 16V
• Analysis: Transient (.tran)

• Input: Pulse waveform
• Op-amp output: HIGH/LOW switching
• Alarm output: ON/OFF response

R. L. Boylestad and L. Nashelsky, Electronic Devices and Circuit Theory, 11th ed., Pearson, 2013.

• Door and window alarm systems
• Intruder detection systems
• Basic security circuits

Thangavikraman Ramachandran
B.E Electronics and Communication Engineering (Pre-final Year)

This project demonstrates practical analog circuit design and simulation using LTspice, focusing on comparator-based decision making and transistor switching behavior.