Infrared Alarm Barrier Circuit

This Infrared Alarm Barrier Circuit show how to use light which we cannot see to make tripwire alarm.

It work like beam of light for small fences.

When someone walk in front of light and break it, loud alarm make big noise to warn and scare person.

It is fun project to do but real home security system is better and more safe for house.

Circuit Working Infrared Light Alarm Transmitter Circuit:

Parts List of Infrared Light Alarm Transmitter Circuit:

This Infrared Alarm Barrier Circuit is to find people when they come inside from small gate, hallway or door.

Transmitter make one invisible infrared light beam when someone walk in front of it then the receiver make buzzing sound.

This how infrared alarm system work:

Transmitter and receiver circuit work for few meter distance and they do not get confuse from normal room light.

Only sometimes if sunlight is very strong and direct on sensor we need extra filter.

Transmitter use 36 kHz signal to turn ON and OFF the infrared LED IRED.

Because infrared sensor does not work good with steady light so this signal is modulated around 300 Hz.

This help detector ignore background light and only sees the real signal.

Transmitter use two CMOS oscillator chip like TLC555 or 7555, or uses one TLC556 or 7556 instead.

IC1 make 300 H and IC2 make 36 kHz signal.

Transistor T1 gives power to IRED LD274 with strong current.

We set exact 36 kHz frequency using P1.

If we want to use less power and do not need big range then we can increase R5 resistor.

Formulas:

Below is simple formula used with 555 IC in astable mode and this mode is used to make pulse width modulation PWM:

Duty Cycle = (THIGH / T) × 100

where:

• Duty cycle tell how much percent of time the output stay HIGH in one cycle.
• THIGH is time in seconds the output stay HIGH.
• T is total time in seconds for one full cycle.

Understand easy way:

This formula show how much time output is HIGH compare to full cycle time.

We multiply by 100 to get duty cycle in percentage.

Why it matter in PWM?

PWM is used to give power to load like LED or motor.

More Duty Cycle like THIGH close to T:

Output HIGH for long time → LED is more bright for motor and is more fast.

Less Duty Cycle like THIGH small than T:

Output HIGH for short time → LED is more dim and motor is more slow.

How duty cycle change in 555 IC?

Normal 555 astable circuit have duty cycle near 50% which is HIGH time almost same as total cycle.

But we can change it.

Use potentiometer to change R2 resistor.

This changes how fast capacitor charges which is change THIGH.

So duty cycle also change.

More control:

Some special circuit with extra parts can make fixed or adjustable duty cycle more than 50%.

Remember this:

Using duty cycle formula help to know how much time output is HIGH in one full cycle.

This is very useful when using 555 IC for control power in LED, motor, etc.

Circuit Working for Infrared Alarm Barrier Receiver:

Parts List of Infrared Alarm Barrier Receiver Circuit:

The CMOS 555 receiver does not make any noise if sensor still see infrared light from transmitter.

Parts D1 and C2 work like low frequency rectifier and they help reduce the 300 Hz signal effect from transmitter.

When someone breaks the light beam the IC 555 oscillator makes warning sound.

In circuit diagram test we can see average DC voltage using digital voltmeter DVM in light and dark.

Most waveforms in test points look like sawtooth or square which are in rectangular shape.

How to Build:

For Building an Infrared Alarm Barrier Receiver Circuit includes assembling the transmitter and receiver connection steps.

Transmitter Circuit:

• Put TLC555 IC1 and IC2 on breadboard.
• Make 300Hz signal and Join pins 2, 6 and 7 of IC1 together.
• Connect pin 4 and pin 8 of IC1 to positive power Vcc.
• Connect pin 5 of IC1 and IC2 to ground using C2 and C4 capacitor.
• Pin 7 of IC2 goes to preset P1.
• One side of P1 goes to Vcc and other side to ground.
• Connect pins 2 and 6 to resistor R2 100k and preset P1.
• Pin 3 of IC1 goes to pin 4 of IC2.
• Pin 3 of IC2 goes to base of transistor T1 using resistor R4 330k.
• Emitter of T1 goes to IR diode D1 using resistor R5.
• Collector of T1 goes to positive power Vcc.
• Cathode of IRED LD274 connects to ground and anode connects to emitter of T1.
• Put resistor R5 18Ω in series with LD274 IRED to control current.
• Use capacitor C5 10µF between Vcc and ground for stable work.

Receiver Circuit:

• Make 36kHz source and put TLC555 IC2 on breadboard.
• Join pins 2 and 6 of IC2 with resistor R3.
• Pin 4 of IC2 connect to output of IC1 using diode D1 BAT85.
• Pin 5 of IC2 goes to ground using capacitor C4 100nF.
• Pin 3 of IC2 goes to piezo buzzer.

Testing:

• Give power to circuit.
• If IR beam is not blocked then buzzer stays quiet.
• When something blocks the beam then buzzer turn ON like an alarm sound

Note:

• Be careful with electronic parts and always check all wire and connection before turning ON the power.

Conclusion:

This Infrared Alarm Barrier Circuit is good for security.

We can use it to watch gates, stairs or private places.

It is cheap and works well to find if someone enters our area.

We can use it inside house or outside.

References:

Simple IR barrier sensor for arduino