Simple Infrared Alarm Barrier Circuit

This circuit shows you how to build a tripwire alarm using invisible light.

Imagine a light beam like a fence.

If someone walks through the beam interrupting it, a loud alarm goes off to scare them away and let you know someone is there.

This is a fun project but remember real security systems are more complex and important for keeping your home safe.

Circuit Working Infrared Light Alarm Transmitter Circuit:

Parts List of Infrared Light Alarm Transmitter Circuit:

This infrared alarm system is designed for detecting individuals passing through doorways, corridors and small gates.

The transmitter emits an invisible infrared light beam and the buzzer in the receiver activates when the beam is interrupted by a person passing through it.

Here is a working process of infrared barrier alarm:

The transmitter and receiver circuits in this infrared alarm system are tailored for a range of several meters, almost unaffected by ambient light conditions.

In rare instances of the receiver sensor being exposed to intense direct sunlight additional screening measures may be necessary.

The transmitter operates by modulating a 36-kHz carrier used to pulse the Infrared Emitting Diode IRED on and off.

This modulation occurs at a rate of about 300 Hz, as continuous incidence of infrared light does not yield optimal responses from most infrared sensors.

Switching the IR source off briefly allows the IR detectors to recover optimizing their ability to minimize responses to ambient light.

The transmitter comprises two oscillators using the CMOS version TLC555 or 7555.

Alternatively, a single TLC556 or 7556 can replace the two 555 ICs.

IC1 serves as the 300Hz generator and IC2 as the 36kHz source.

The IRED type LD274 is pulsed at a high peak current via driver transistor T1.

Adjusting preset P1 ensures a carrier frequency of precisely 36kHz.

If your application requires a shorter IR beam distance you can increase the value of resistor R5 to save on current consumption.

Formulas:

Below mentioned formula applies to a 555 IC configured in astable multivibrator mode, which is commonly used to generate a Pulse Width Modulation PWM:

Duty Cycle = (THIGH / T) * 100

where,

• Duty Cycle: This indicates the proportion of time that the 555 IC output is in the HIGH state throughout the course of one output waveform cycle.
• It is a number that ranges from 0% (constantly LOW output) to 100% (constantly HIGH output).
• THIGH: This is the amount of time, measured in seconds, that the 555 IC output remains in the HIGH state for throughout a single cycle.
• T: This is the entire time (measured in seconds) that the output waveform takes to complete one cycle.

Recognizing the connection:

In essence, the formula determines the percentage of the cycle during which the output is HIGH in relation to the whole cycle length.

We may represent it as a percentage (duty cycle) by multiplying by 100.

Why does this matter in circuits using PWM?

By altering the duty cycle, PWM signals can regulate the average power supplied to a load (such as an LED or motor).

Greater Duty Cycle (THIGH closer to T): This indicates that the output stays in the HIGH state longer, providing the load with more power (faster motor, brighter LED).

Reduced Duty Cycle (THIGH is shorter than T): This indicates that the output is in the HIGH state for a shorter period of time, which implies the load (slower motor, dimmer LED) receives less power.

What is the effect of duty cycle on the 555 IC circuit?

The duty cycle of a typical 555 astable multivibrator circuit is around 50% (THIGH is approximately equal to T).

Nonetheless, the circuit may be altered to regulate the duty cycle:

Using a potentiometer: You may change the resistance of resistor R2 (see a schematic of a 555 IC astable multivibrator) and therefore the capacitors (THIGH) charging time.

The duty cycle is altered as a result.

Adding extra components: Certain circuit arrangements that include extra parts can enable fixed or programmable duty cycles that exceed 50%.

Note:

The above duty cycle formula, aids in determining the proportion of a whole cycle when the output of a 555 IC in astable mode is HIGH.

In PWM applications, this number is essential for comprehending and managing the power applied to a load.

Circuit Working for Infrared Alarm Barrier Receiver:

Parts List of Infrared Alarm Barrier Receiver Circuit:

The receiver, also based on a CMOS 555 remains silent as long as the sensor detects the infrared light from the transmitter.

Components D1 and C2 function as a low frequency rectifier canceling the effect of the 300Hz modulation on the transmitter signal.

When the infrared light beam is interrupted the 555 oscillator is enabled producing a warning tone.

The test values in the circuit diagram represent average DC levels measured with a digital voltmeter DVM under light and no light conditions.

Most test points exhibit rectangular or sawtooth waveforms.

How to Build:

Building an infrared barrier alarm involves assembling the transmitter and receiver circuits.

Transmitter Circuit:

• Connect the IC TLC555 IC1 and IC2 to the breadboard.
• Set up the 300Hz generator: connect pins 2, 6, and 7 of IC1 together.
• Connect pin 4 to positive supply.
• Connect pin 5 to ground via C2 and C4.
• Connect pin 7 of IC2 to P1, with one end connected to Vcc and the other to ground.
• Connect pins 2 and 6 to resistor R2 100k and preset P1.
• Connect pin 3 of IC1 to pin 4 of IC2
• Connect pin 3 of IC2 to the base of transistor T1 via resistor R4 330k.
• Connect the collector of T1 to positive supply and the emitter to IR diode D1 via R5.
• Connect the anode of the LD274 IRED to the emitter of T1 and the cathode to ground.
• Connect a resistor R5 18Ω in series with the LD274 IRED to limit the current.
• Connect a capacitor C5 10μF between positive supply and ground for stabilization.

Receiver Circuit:

• Set up the 36 kHz source: connect another IC TLC555 IC2 to the breadboard.
• Connect pins 2 , 6 of IC2 together with R3.
• Connect pin 4 of IC2 to the output of IC1 through diode D1 BAT85.
• Connect pin 5 via to ground through a C4 100nF capacitor.
• Connect pin 3 of IC2 to piezo buzzer

Testing:

• Power the circuit.
• Ensure the infrared beam is uninterrupted to keep the buzzer silent.
• Observe the alarm activation when the beam is interrupted.

Note:

• Remember to exercise caution when working with electronic components and circuits, and double check your connections before applying power.

Conclusion:

The Infrared Alarm Barrier Circuit is commonly used in security applications to monitor doorways, corridors, or restricted areas.

It provides a reliable and cost effective means of detecting unauthorized access or movement in a specific zone.

Additionally, the modulated infrared signal helps the system cope with variations in ambient light conditions making it suitable for indoor and outdoor use.

References:

Simple IR barrier sensor for arduino