This Infrared Alarm Barrier Circuit shows how to use light which we cannot see to make tripwire alarm; it also 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:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 4.7k | 2 |
| 100k | 1 | |
| 330Ω | 1 | |
| 18Ω | 1 | |
| Preset 25k | 1 | |
| Capacitors | Ceramic 10nF | 2 |
| Ceramic 1nF | 2 | |
| Ceramic 100nF | 2 | |
| Electrolytic 10μF 16V | 1 | |
| Semiconductors | IC 555 | 2 |
| Transistor BD140 | 1 | |
| IR LED LD274 or similar | 1 |
To begin with, 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:
Here, 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 and
The transmitter uses a 36 kHz signal to switch the infrared (IR) LED ON and OFF because the IR sensor does not respond well to steady light, hence, this signal is modulated at around 300 Hz.
Also, 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 and transistor T1 gives power to IRED LD274 with strong current.
We can set exact 36 kHz frequency using P1 and if we want to use less power and do not need big range then we can increase R5 resistor.
Formulas:
The following formula applies to the 555 IC in astable mode, which generates 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 and we can multiply by 100 to get duty cycle in percentage.
Why it matter in PWM?
PWM supplies power to loads such as LEDs or motors.
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, by using potentiometer R2 resistor.
Also, 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 and 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:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 100k | 1 |
| 10k | 1 | |
| 22k | 1 | |
| Capacitors | Ceramic 100nF | 1 |
| Electrolytic 47μF 16V | 2 | |
| Electrolytic 1μF 16V | 1 | |
| Semiconductors | IC TSOP1738 | 1 |
| IC 555 | 1 | |
| Diode BAT85 | 1 | |
| Diode 1N4148 | 1 | |
| Buzzer | 1 |
The CMOS 555 receiver does not make any noise if sensor still see infrared light from transmitter.
Parts like D1 and C2 work like low frequency rectifier and they help reduce the 300 Hz signal effect from transmitter.
So 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:
- First, put TLC555 IC1 and IC2 on breadboard and make 300Hz signal and Join pins 2, 6 and 7 of IC1 together.
- Next, connect pin 4 and pin 8 of IC1 to positive power Vcc.
- Then connect pin 5 of IC1 and IC2 to ground using C2 and C4 capacitor.
- Here, pin 7 of IC2 goes to preset P1 with one side of P1 goes to Vcc and other side to ground.
- Also, connect pins 2 and 6 to resistor R2 100k and preset P1.
- After that, pin 3 of IC1 goes to pin 4 of IC2 and pin 3 of IC2 goes to base of transistor T1 using resistor R4 330k.
- Next, emitter of T1 goes to IR diode D1 using resistor R5 and collector of T1 goes to positive power Vcc.
- Then cathode of IRED LD274 connects to ground and anode connects to emitter of T1.
- Now put resistor R5 18Ω in series with LD274 IRED to control current and use capacitor C5 10µF between Vcc and ground for stable work.
Receiver Circuit:
- Now make 36kHz source and put TLC555 IC2 on breadboard and join pins 2 and 6 of IC2 with resistor R3.
- Next, pin 4 of IC2 connect to output of IC1 using diode D1 BAT85.
- After that, pin 5 of IC2 goes to ground using capacitor C4 100nF.
- Pin 3 of IC2 goes to piezo buzzer.
- First, switch on the circuit, if nothing blocks the IR beam, the buzzer stays quiet and when an object blocks the beam, the buzzer turns ON and produces an alarm sound.
Note:
- Be careful with electronic parts and always check all wire and connection before turning ON the power.
Conclusion:
To conclude, this Infrared Alarm Barrier Circuit is good for security, also we can use it to watch gates, stairs or private places.
Furthermore, it is cheap and works well to find if someone enters our area; and we can use it inside house or outside also.
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