This article shows you how to build a cool alarm system that uses invisible light beams to detect intruders!
It has two parts: a transmitter and a receiver.
The transmitter sends a beam of infrared light across a room.
If someone walks through the beam, it triggers the alarm.
This is a great project to learn about electronics but for a real home security system, it is best to buy one from a store.
What is a Infrared IR Intruder Alarm Circuit:
An Infrared IR Intruder Alarm Circuit is a security system that uses infrared technology to detect the presence of an intruder.
Infrared sensors are capable of detecting infrared radiation emitted by warm objects or individuals.
The basic idea behind an IR intruder alarm circuit is to use an IR transmitter and receiver pair to create a barrier or zone.
When an intruder crosses this zone, it interrupts the infrared beam, triggering the alarm.
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 table organizes the components along with their descriptions and quantities for easy reference.
The transmitter circuit is illustrated in the diagram above and utilizes a IC 555 timer configured as an astable multivibrator.
The infrared emitter LED1 is controlled to oscillate at a frequency of approximately 5KHz.
This pulsing mechanism provides several advantages, including:
Frequency of Oscillation ≈ 5 KHz
- Encoding the IR pulse to distinguish the signal from other light sources.
- AC coupling capability for resistance to ambient light level changes.
- Power efficiency especially crucial for battery powered transmitters.
Transmission Frequency Adjustment:
The transmission frequency can be fine tuned based on the practical positions of the transmitter and receiver.
Formula:
Below mentioned is the formula to calculate the frequency of an 555 astable circuit with the given component values:
Frequency (f) = 1.44 / (R1 + RV1 + 2R2) * C1
where,
- f is the frequency in hertz Hz
- R1 is the resistance of resistor R1 in ohms Ω
- RV1 is the preset in in ohms Ω
- R2 is the resistance of resistor R2 in ohms Ω
- C1 is the capacitance of capacitor C1 in Farads F
Receiver Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | 47k (all 1/4 W CFR) | 3 |
| 100k (all 1/4 W CFR) | 3 | |
| 100Ω (all 1/4 W CFR) | 1 | |
| 5.6k (all 1/4 W CFR) | 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 | |
| Other Components | Relay 12V | 1 |
The receiver circuit, as shown in the diagram above incorporates an infrared receiver diode LED1 reverse biased by R1.
When struck by infrared light the diodes conductivity increases, causing a voltage drop at the junction of R1 and LED1.
Key elements of the receiver circuit include:
Op-Amp Configuration:
R2 and R3 set input to 50% power supply range
Amplifier gain determination R4, R5 and C2
Average gain increase at 5KHz many Thousands.
The output of the amplifier IC1 generates an AC signal of approximately 5KHz when the transmitted signal is detected by the receiver.
Further circuitry involves:
Voltage doubler circuitry D1,D2 and C4
Transistor activation Q1 and Relay
The relay is activated when the filter capacitor C4 is adequately charged and it deactivates when the transmission is cut off or disturbed.
How to Build:
Building the IR intruder alarm circuit involves constructing both the transmitter and receiver circuits.
Transmitter Circuit:
- Connect the components as per the given circuit diagram.
- Set up the IC 555 as an astable multivibrator.
- Connect the infrared emitter LED1 to the output of the timer.
- Adjust the values of the resistor R and capacitor C to achieve the desired oscillation frequency approx 5KHz.
- Ensure the circuit is powered by a stable power supply or battery.
Receiver Circuit:
- Connect the components as per the given circuit diagram:
- Reverse bias the infrared receiver diode LED1 using resistor R1.
- Set up the operational amplifier IC IC1 as a non inverting AC amplifier.
- Bias the input using resistors R2 and R3 to set it at 50% of the power supply range.
- Determine the amplifiers gain using resistors R4, R5 and capacitor C2.
- The gain increases significantly at the desired frequency approx 5KHz.
- Utilize diodes D1 and D2 for voltage doubling.
- Capacitor C4 charges to activate the transistor Q1 and relay.
- Add diode D3 for back EMF shielding.
- Capacitors C3 and C5 provide power supply decoupling to eliminate spikes generated by relay switching.
- Connect the relay to the alarm or alert system.
- Ensure the circuit is powered by a stable power supply.
Alignment and Testing:
- Align the transmitter and receiver units in a line ensuring that the infrared beam from the transmitter reaches the photodiode of the receiver.
- Power up the circuits.
- Test the circuit by obstructing the IR beam, the relay should activate triggering the alarm.
- Fine tune the transmitter frequency using the preset potentiometer for optimal performance.
Note:
- Adjustments and experimentation may be necessary based on specific requirements and environmental conditions.
Conclusion:
This construction of an advanced IR intruder alarm circuit ensuring enhanced security through precise alignment, pulsing technology, and robust receiver circuitry.
Experimentation with the transmitter and receiver positions as well as frequency adjustments allows for customization based on practical scenarios.