Here is a very simple as well as very useful project anti bag snatching alarm, used in bag or suitcase in order to prevent from snatching. The sound produced by anti bag snatching alarm is like police horn to get attention of people when someone attempt to snatch your bag or suitcase.

Circuit Description of anti bag snatching alarm

The heart of this entire circuit anti bag snatching alarm is operational amplifier IC CA3140 (IC₁), configured as a comparator. The two inputs (inverting and non - inverting) is given to pin no 3 and 2 of operational amplifier respectively and output is obtained from pin no 6. Here IC₂ (timer IC NE555) is used as monostable multivibrator. The timing component of anti bag snatching alarm is R₅, VR₁, and capacitor C₂ with the given value in this circuit diagram lets the time of timer is about 1 minute.

For audio section, IC₃ is used as alarm tone generator with an inbuilt oscillator. Finally the output is obtained from pin no 3 of IC₃ and amplified by transistor T₁ in order to get desire level and lastly fed to loudspeaker for output.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R₂, R₃ = 100 KΩ

R₄, R₆ = 10 KΩ

R₅ = 10 MΩ

R₇ = 330 Ω

R₈ = 220 KΩ

R₉ = 1 KΩ

VR₁ = 10 MΩ

Capacitors

C₁, C₃ = 0.0047 µF

C₂ = 4.7 µF/16V

C₄ = 0.01 µF

Semiconductors

IC₁ = CA3140 (operational amplifier)

IC₂ = NE555 (timer IC)

IC₃ = UM3561 (complex ROM with an inbuilt oscillator)

T₁ = BD139

ZD₁ = 3.3V 500mA

Miscellaneous

SW₁ = ON/OFF switch

L₁ = speaker 8Ω 1W

Mono plug, mono jack 8