Main objective of this project is to design a security system based on a photo-sensing arrangement. It uses dual comparator LM393 that is widely used in many commercial applications. Here, it is used to sense the input signal through a light-dependent resistor (LDR). Comparator output drives a buzzer and a relay.
This concept is very useful as a burglar deterrent in places like banks, malls, jewellery stores, hotels and homes. Fig. 1 shows the author’s prototype.
Circuit and working of electronic eye security system
Circuit diagram for the electronic eye security system is shown in Fig. 2. It is built around 12V-0-12V, 750mA secondary transformer (X1), 1N4007 rectifier diodes (D1 through D3), LDR (LDR1), filter capacitors C1 and C2, 5V voltage regulator 7805 (IC1), dual comparator LM393 (IC2), 12V multi-tone high-gain buzzer (PZ1), transistor TIP122 (T1) for driving PZ1, transistor BC547 (T2) for driving 12V, 1C/O relay for controlling an electrical appliance or bulb (B1), and 10-kilo-ohm potmeter VR1.
When light falls on LDR1, its resistance drastically decreases, which leads to triggering an alarm to alert the user.
This system is suitable for securing cash boxes and lockers. The circuit is placed inside the cash box or locker in such a way that, when the burglar opens it and uses a torch light to find the valuables, light falls on LDR1, which acts as an electronic eye.
Signal output from LDR1 is fed to IC2. Output from IC2 activates the alarm when light falls on LDR1 during a burglary attempt. At the same time, bulb B1 glows as a visual alert to thwart the burglary attempt.
Case 1. If reference voltage at pin 3 of IC2 is less than sensor voltage at pin 2 of IC2, output goes low automatically. This indicates that no light is falling on LDR1. Low output of IC2 is fed to T1 and T2. As a result, both are in cut-off state and so no current flows through the buzzer, keeping it in silence mode. Similarly, no current flows in the relay, and so B1 does not glow.
Case 2. If reference voltage at pin 3 of IC2 is greater than sensor voltage at pin 2 of IC2, output goes high automatically. This indicates that light is falling on LDR1. High output of IC2 is fed to T1 and T2. As a result, both transistors are in on (active) state. Current flows through the buzzer and relay. The buzzer produces a loud alarm to alert you or people around you and, at the same time, B1 glows as the circuit completes through relay RL1’s contacts.
Construction and testing
An actual-size, single-side PCB for the electronic security system is shown in Fig. 3 and its component layout in Fig. 4. After assembling the circuit on the PCB, enclose it in a suitable plastic box.
Download PCB and Component layout PDFs: click here
Pamarthi Kanakaraja is assistant professor in Usha Rama College of Engineering and Technology, Andhra Pradesh