This article explains how one can design an innovative alarm system that detects possible attackers passing through a invisible light beams.
The circuit consists of two components: a transmitter and a receiver.
The circuits transmitter puts out an infrared light beam across the room.
When someone passes by a light source an LED alerts with an alarm sound.
This project gives an excellent opportunity to learn more about electronics.
What is a Infrared IR Intruder Alarm Circuit:
One type of security devise 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 expressed 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 | |
| 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.
- Be sure a steady power source or battery is used to power the circuit.
Receiver Circuit:
- Connect the components according to the related circuit diagram:
- Reverse bias the infrared receiver diode LED1 with resistor R1.
- Design the operational amplifier IC1 as a non-inverting AC amplifier.
- Bias the input with resistors R2 and R3 to set it to 50% of the power supply range.
- Calculate the amplifiers gain using resistors R4, R5 and capacitor C2.
- The gain improves considerably at a perfect frequency of around 5KHz.
- Use diodes D1 and D2 to double the voltage.
- Capacitor C4 charges to turn ON the transistor Q1 and relay.
- Add diode D3 to back EMF protection.
- Capacitors C3 and C5 provide power supply decoupling which reduces spikes caused by relay switching.
- Connect the relay to the alarm or warning system.
- Be sure the circuit has a reliable power source.
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 actual circuit design.
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