This article explains how one can build an innovative alarm system that uses invisible light beams to detect possible Intruder.
There are two parts in the circuit: a transmitter and a receiver.
The transmitter sends an infrared light beam across a room.
An indicator known as an alarm is triggered when someone walks through a beam.
An wonderful method to learn about electronics is through this project.
What is a Infrared IR Intruder Alarm Circuit:
One type of security system that uses infrared technology to identify the presence of an intruder is an Infrared IR Intruder Alarm Circuit.
When warm things or people produce infrared radiation than infrared sensors can detect that.
Using an IR transmitter and receiver pair to create a barrier or zone is the basic idea of an intruder alarm circuit.
The alarm is activated when an intruder crosses this area because it disrupts the infrared beam.
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 |
The transmitter circuit which uses an IC 555 timer set as an astable multivibrator is shown in the above circuit diagram.
The infrared emitter LED1 is configured to oscillate at a frequency around 5KHz.
Some advantages of this oscillating mechanism are as follows:
Frequency of Oscillation = 5 KHz
- The infrared pulse needs to be encoded in order to identify it from other light sources.
- AC coupling ability for managing changes in the amount of light in the surroundings.
- Additionally battery operated transmitters need to be power efficient.
Transmission Frequency Adjustment:
Based on the transmitter and receivers actual locations the transmission frequency can be adjusted.
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 |
A reverse biased infrared receiver diode LED1 is integrated into the receiver circuit as shown in the above diagram.
A voltage drop develops at the junction of R1 and LED1 as the diodes resistance rises in response to infrared light.
The following are important components of the receiver circuit.
Op-Amp Configuration:
R2 and R3 have their inputs set to 50% of the power supply range.
Calculation of amplifier gain are R4, R5 and C2
At 5KHz the average gain increased by thousands.
When the receiver detects the sent signal the amplifier IC1s output produces an AC signal of about 5 kHz.
Additional circuitry consists of:
- D1, D2 and C4 are the voltage doubler circuits
- Relay and Q1 transistor activation
When the filter capacitor C4 is sufficiently charged the relay is triggered, when the transmission is interrupted or switched off the relay deactivates.
How to Build:
Below are the building steps for Simple Infrared (IR) Intruder Alarm Circuit:
Transmitter Circuit:
- As shown in the circuit diagram connect the parts.
- The IC 555 should be configured as an astable multivibrator.
- Join the LED1 infrared emitter to the timers ICs output.
- To get the desired oscillation frequency which is around 5KHz adjust the values of the resistor R and capacitor C.
- Make sure a steady power source or battery is used to power the circuit.
Receiver Circuit:
- Connect the components as per the given circuit diagram:
- Reverse bias the infrared receiver diode LED1 using resistor R1.
- Adjust the operational amplifier 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.
- Calculate the amplifiers gain using resistors R4, R5 and capacitor C2.
- The gain increases significantly at the desired frequency approx 5KHz.
- Use 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 preventing the IR beam the relay should activate triggering the alarm.
- Fine tune the transmitter frequency using the preset potentiometer for best performance.
Note:
- Experiments and modifications are required depending on particular needs and environmental conditions.
Conclusion:
With its accurate alignment, vibrating technology and sturdy receiver electronics this smart intruder alarm circuit construction provides greater safety.
Adjusting the frequency and experimenting with the transmitter and receiver sites allows modification based on real life scenarios.
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