Simple Electronic Gatekeeper Circuit

This circuit is like a tiny guard for your door.

It uses sensors to see if someone is coming or going through your gate.

These sensors can be like light beams or pressure pads.

If someone sneaks through without permission, the circuit can trigger an alarm or send you a message to let you know.

This way, you can keep your space secure and know when someone is coming or going.

Circuit Working:

Parts List:

This circuit serves as a gatekeeper alerting you when someone passes through the gate.

The alarm can be an AC bell or a lamp, which activates for one minute before stopping if the light barrier is restored.

Infrared rays are employed as the light barrier activating the alarm system through a phototransistor.

The high gain NPN darlington phototransistor L14F1 conducts when exposed to IR rays bringing its collector to ground potential.

IC functions as a simple voltage comparator with a potential divider R2 and R3 connected to its inverting input, providing half the supply voltage 6V to this input.

The non inverting input of IC is linked to the phototransistors collector.

Normally, ICs output is low while T1 is conducting.

However, when the IR beam is broken the collector of T1 goes high causing the voltage at the non inverting input of IC to exceed that at the inverting input resulting in a high output.

This high output triggers the relay driver T2, turning on the relay.

Capacitor C1 introduces a short delay at the non inverting input of IC to prevent false triggering while C2 keeps the base of T2 high for a brief period even if the IR rays are restored.

It is crucial to align the IR rays precisely with the phototransistor to keep the alarm off.

The circuits normal range is 2 meters extendable to 5 meters with a convergent lens in front of the IR LEDs.

If an AC alarm is not needed a buzzer can be used in place of the relay.

Additionally, a laser pointer can substitute for the IR LEDs increasing the range to 25 meters.

However, if a laser is used precautions must be taken to prevent direct viewing.

Enclose the phototransistor in a small case with an opening in front to prevent ambient light from entering.

Lastly, fix the IR LEDs on one gate pillar and the phototransistor on the opposite pillar with exact alignment.

Formula:

The following formula is used to determine the gain G of an inverting amplifier that uses the LM741 IC:

G = −R_f​​ / R_in​

where,

• The input resistor is represented by R_in and the feedback resistor by R_f.

Note:

For comprehensive specs, common application circuits, and more information, consult the LM741 datasheet.

For complete and current information, always consult the individual LM741 datasheet since various manufacturers may have slightly different specs and operating conditions.

How to Build:

To build a Simple Electronic Gatekeeper Circuit you need to follow the below mentioned assembling steps:-

Connect the Phototransistor L14F1:

• Connect the collector of the phototransistor to the inverting input of IC.
• Connect the emitter to the ground.

Connect the Darlington Transistor T1:

• Connect the base of T1 to the cathode of the IR LED.
• Connect the emitter of T1 to the ground.

Connect the Voltage Comparator IC:

• Connect a potential divider R2 and R3 between the positive supply and ground.
• Connect the non inverting input of IC to the junction of R2 and R3.
• Connect the inverting input of IC to the collector of the phototransistor.

Connect the Relay:

• Connect the relay to the output of the voltage comparator IC through the transistor T2.

Connect the Capacitors C1, C2:

• Connect C1 between the collector of the phototransistor and the inverting input of IC.
• Connect C2 between the base of T2 and ground.

Align the Components:

• Align the IR LEDs with the phototransistor and ensure they are positioned correctly to create a light barrier.

Test the Circuit:

• Power on the circuit and test it by interrupting the IR beam.
• The alarm should activate when the beam is interrupted and stop when it is restored.

Adjustments:

• Adjust the circuit as needed for optimal performance, such as adjusting the sensitivity of the phototransistor or the delay capacitor.

Note:

• Please note that working with electronic circuits involves handling potentially dangerous components and voltages.
• Ensure that you have the necessary skills and take appropriate safety precautions when building and testing the circuit.

Conclusion:

An electronic gatekeeper circuit is a security system designed to monitor and control access to a specific area, typically a gate or entrance.

It employs sensors to detect movement or presence triggering an alarm or notification to alert users of unauthorized access.

These circuits enhance security by providing real time monitoring and control capabilities contributing to the overall safety and protection of properties and facilities.

References:

Datasheet IC LM741

Datasheet L14F1