Below is a circuit design diagram which illustrates the flow of a laser alarm system.
Referring to circuit diagram it is seen that a TL072 op-amp (IC1.A) is configured as a voltage comparator, placed in between the adjustable voltage driver P1/R4 and the light-dependent voltage which consists of photodiode D1 and R3 – a fixed resistor. As the laser beam receives a distraction from a foreign agent, the voltage on comparator pin drops to 2 below that at pin 3, thereby enabling the agent swing to positive voltage supply and enable an alarm situation.
As the laser alarm can detect any foreign agents, so is the alarm can be set in a more sophisticated fashion, where it can bypass accidental interrupts from agents, like an insect. This is accomplished as the Resistor R2 provides a level of hysteresis, thereby prevent oscillation when two comparator input voltage rests in almost equal state. In order to set a faster response method, it can be achieved by reducing the value to 1 µF.
A laser beam system is easier to setup, either as a single or a separate entity. If a single box is maintained to setup the alarm, then it is to be made sure that the photodiode can’t have direct contact with the laser beam. Assembling the components and the circuit in a breadboard, it should be mounted in a black box having a hole. A black drinking straw should pass through the hole to enable light flow from the direction of the laser beam to enter. Setting up the system properly makes the laser beam act even with direct sunlight, as it cannot affect the operation of the photodiode.
Article Written and Submitted by Mr. Dhrubajyoti Biswas