Intruder alarm is very common project for diploma or basic level. Here, by dreamlover technology a verified project on intruder is published, used in door of your house for sound an alarm when anyone open or pushed the door. The circuit of intruder alarm can be used against thieves or intruders.

Circuit description of intruder alarm

The project intruder alarm consist two circuits each of transmitter and receiver separately. Transmitter section comprising a laser diode and power is given from a 9V power supply. Here the receiving section consists of LDR for sensor and work on principle of LDR. When light falling to LDR from laser diode provides base current to transistor T₁ which start conducting (but not T₂) and the alarm remains off.

When door is pushed, light incident on the LDR is interrupted and it offer high resistance which stop conducting transistor T₁ but transistor T₂ receive base current and start conducting. The input is given to AND gate N₁ from the emitter of transistor T₂. Here IC₂ work as latch when high output from AND gate N₁ is connected to pin 1 and 14 respectively. High output form output pin 12 of IC₂ is given to base of transistor T₃ through R₇ and it cause transistor conduction and consequent sounding of the alarm.

Dreamlover Technology Note: While testing at dreamlover technology Lab, a laser torch in place of the transmitter was used.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R₂, R₆, R₈ = 1 KΩ

R₃ = 2.2 KΩ

R₄ = 10 KΩ

R₅ = 100 Ω

R₇ = 2.2 KΩ

Semiconductors

IC₁ (N₁) = 7408

IC₂ = 7473 JK flip-flop

T₁ = BEL187

T₂, T₃ = SL100

LED₁, LED₂ = RED

LD₁ = Laser diode

Miscellaneous

9V battery

SW₁, SW₂ = On/off switch

SW₃ = push-to-on switch

Piezo buzzer

LDR

Related Project

1. Wireless Controlled Doorbell controlling range of wireless doorbell is 100M.
2. 2-Tone Door Bell generates ding-dong sound similar to an electrical bell.
3. Simple Electronics Siren simple circuit of siren build around single chip CD4011 (IC₁)
4. Melody Doorbell use 3V DC battery to operate instead of AC mains, with good quality sound.
5. Beeper and Visual Indicator visual indicator lights up with each beep having the same time period.