This article tell how to make new type of Simple Infrared (IR) Intruder Alarm Circuit.
It can find person who walk through invisible light beam.
Circuit have two main part: one transmitter and other one is receiver.
Transmitter send out one infrared light beam across a room.
If someone goes in front of light the LED blink and alarm makes sound.
This project is good for learning more about electronics.
What is a Infrared IR Intruder Alarm Circuit:
One type of security device used in infrared technology is to find intruder is Infrared IR Intruder Alarm Circuit.
When warm body or person make through then infrared light sensor can see it.
Main idea is to use IR transmitter and receiver to make one barrier or zone.
When intruder walk through this area they break the IR beam and alarm starts making sound.
Transmitter Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | 470Ω (all 1/4 W CFR) | 2 |
| 2.2k (all 1/4 W CFR) | 1 | |
| Preset 10k | 1 | |
| Capacitors | Ceramic 47nF | 1 |
| Electrolytic 10µF 25V | 1 | |
| Semiconductors | IC 555 | 1 |
| IR Emitter LED | 1 |
This transmitter circuit uses IC 555 timer work like astable multivibrator which we can see in above diagram.
Infrared LED1 make light blink at around 5KHz speed.
Some good things of this blinking system are:
- Blinking frequency is 5KHz
- Its pulse help to know IR light from other normal lights
- AC coupling help to handle light change in the room
- Battery transmitter also needs to save power
Adjust frequency of transmission depend on transmitter and receiver both.
Formula:
Below formula is to find frequency of 555 astable circuit using parts value:
Frequency (f) = 1.44 / (R1 + RV1 + 2R2) × C1
where:
- f is frequency in hertz Hz
- R1 is resistor R1 value in ohms Ω
- RV1 is preset value in ohms Ω
- R2 is resistor R2 value in ohms Ω
- C1 is capacitor C1 value in Farads F
Receiver Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors (all resistors are 1/4 W CFR) | 47k | 3 |
| 100k | 3 | |
| 100Ω | 1 | |
| 5.6k | 1 | |
| Capacitors | Ceramic 10nF | 1 |
| Ceramic 100nF | 1 | |
| Electrolytic 2.2µF 25V | 2 | |
| Electrolytic 100µF 25V | 1 | |
| Semiconductors | Transistor BC547 | 1 |
| Diodes 1N4148 | 3 | |
| IC 741 | 1 | |
| IR Receiver LED | 1 | |
| Relay 12V | 1 |
One infrared receiver diode LED1 is use in receiver circuit which is reverse biased and we can see this in above circuit diagram.
When IR light comes diode resistance goes up and voltage drop happen at point between R1 and LED1.
Here are main parts in receiver circuit:
Op-Amp Setup:
R2 and R3 give input at half of power supply.
R4, R5 and C2 used to calculate amplifier gain.
At 5KHz gain becomes very high which is even thousand times.
When receiver gets signal Op-Amp IC1 give AC output signal around 5KHz.
Other circuit parts:
D1, D2 and C4 work like voltage doubler.
Relay and Q1 transistor are used for switching.
When C4 get enough charge the relay turn ON.
If signal stops or break then relay turns OFF.
How to Build:
Steps to Build Simple Infrared (IR) Intruder Alarm Circuit is mentioned below:
Transmitter Circuit:
- Connect all parts same like in circuit diagram.
- IC 555 must be set as astable multivibrator.
- Connect LED1 infrared emitter to IC 555 output pin.
- To get around 5KHz frequency change the value of resistor R and capacitor C.
- Use good power source or battery to give power to circuit.
Receiver Circuit:
- Join all parts same like in receiver diagram.
- Make LED1 IR receiver in reverse bias using resistor R1.
- Set IC1 Op-Amp as non-inverting AC amplifier.
- Use resistors R2 and R3 to make input half of power supply.
- Use R4, R5 and C2 to calculate amplifier gain.
- Gain is high at 5KHz frequency.
- Use diode D1 and D2 to double the voltage.
- Capacitor C4 charges and turn ON transistor Q1 and relay.
- Put diode D3 to protect from back current EMF.
- Capacitor C3 and C5 help to stop power noise from relay.
- Connect relay to alarm or any warning system.
- Be sure power supply is good and stable.
Alignment and Testing:
- Place transmitter and receiver in straight line so IR light goes directly to receiver.
- Turn ON the power.
Test it:
- If we block the IR light then relay should turn ON and alarm makes sound.
- Use preset potentiometer to adjust transmitter frequency for better working.
Note:
- We can try changes and testing, depending on what we want or what is our room condition.
Conclusion:
This smart and Simple Infrared (IR) Intruder Alarm Circuit gives more safety because of good alignment, fast working and strong receiver parts.
We can change frequency and test with different place of transmitter and receiver to make it work better for our design.