The post explains a simple laser alarm circuit which can be installed in farms and fields for detecting all possible intrusions, either by a human or an animal and alarming this to the owner, and ensuring an effective protection to the crops against such intrusions. The idea was required by Mr. Mohammed and Mr. Daniel.

Circuit Request#1

Congratulations for all amazing work please give me any circuit for agricultural fields, need to protect the crops from uninvited guests like animals i want to achieve an Active infrared barrier [laser] circuit with distance range of 100 meter or above.

mohammed jilani Mansoori

Circuit Request#2

sir please my grandfather is an orange farmer and he is having a problem with thief's so he ask me to do something that to protect the farm or anything that can alert him when any thief's or any person try to take away any thing from the farm so i decided to install a CCTV camera,so i need a circuit without a camera or if you can help me out sir i have said this but you can create something that can help me out thank you hope to hear from you soon

Daniel Adusei

Simulation and Working

Laser Alarm for Protecting Field Crops against Animals

 The Design


The proposed laser alarm circuit for protecting crops from animals and intruders can be seen in the figure above.

The idea appears extremely straightforward, and employs an IC 555 based monostable multivibrator stage and an LDR detector.

As shown in the design, the laser beam is generated through a laser pointer circuit held at some parallel point across the field fence which requires to be protected.

Since a laser beam has the property of focusing over a given point undistorted and on a straight line, regardless of the distance, the focus in this application is adjusted over an LDR across a specified distance, as indicated in the diagram.

The LDR is enclosed inside a light proof box with a tiny hole which allows only the laser beam to enter while obstructing most of the ambient light around.

As long as the laser beam is held focused over the the LDR, the resistance of the LDR is enabled at a minimum level which could be around 10K to 50K approximately depending on the particular LDR specs.

The low resistance from the LDR ensures a high potential at the base of the associated BC557 transistor rendering it inactive. This in turn keeps the pin#2 of the IC555 monostable at a high potential and the output of the IC at logic zero, so that the relay is held switched OFF.

Now in an even when an intruder (a human or animal) makes an attempt to cross the protected line of fence, cuts or obstructs the laser beam, which instantly causes the LDR resistance to increase and trigger the BC557 device via the 1M resistor.

The BC557 responds to this and conducts grounding pin#2 of the IC and activating the monostable action.

The above procedure forces the pin#3 of the IC to go high and switch ON the relay, the relay contacts possibly being connected with an alarm, sounds the alarm, alerting the field owner regarding the intrusion.

The alarm continues to sound for some moment of time depending on the values of R and C, whose values are directly proportional to the length of the alarm switch ON period.

The above discussed laser alarm circuit can be installed across all the corners of field for ensuring maximum and all round protection for the valuable crops and for ensuring a peaceful sleep to the field owner.

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