Monday, November 3, 2008

Theft preventer alarm

This circuit utilising a 555 timer IC can be used as an alarm system to prevent the theft of your luggage, burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken.

The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which gives out a shrill noise to scare away the burglar.

The wire used to set off the alarm can be made of a thin copper wire like SWG 36 or higher.
You can even use single strands of copper form a power cable.

The circuit operates on a wide range of voltages from 5V to 15V.

The speaker and the circuit could be housed inside a tin can with holes drilled on the speaker side for the sound to come out.

Rangkaian yang menggunakan IC timer 555 ini dapat digunakan sebagai alarm untuk mencegah pencuri menggondol barang-barang atau masuk ke rumah Anda. Alarm akan menyala (ON) ketika kawat tipis (biasanya setipis rambut) putus.

Rangkaian ini menggunakan IC 555 yang dikawati menjadi multivibrator yang tidak stabil untuk menghasilkan frekuensi sekitar 1 kHz yang terdengar cukup menakutkan perampok.

Kabel tipis yang dimaksudkan untuk mematikan alarm dapat dibuat dari kawat tembaga tipis seperti SWG 36 atau bisa juga serat kawat tembaga dari kabel power.

Rangkaian ini beroperasi dalam jangkauan tegangan yang cukup besar yaitu antara 5 hingga 15 V.

Speaker dan rangkaian dapat dimasukkan ke dalam kaleng dengan diberi lubang di depan speaker agar suara bisa keluar.

http://www.electronic-circuits-diagrams.com/alarmsimages/alarmsckt3.shtml

Sunday, November 2, 2008

Infrared Head Phones

Using this low-cost project one can reproduce audio from TV without disturbing others. It does not use any wire connection between TV and headphones. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. Without using any lens, a range of up to 6 metres is possible. Range can be extended by using lenses and reflectors with IR sensors comprising transmitters and receivers.

IR transmitter uses two-stage transistor amplifier to drive two series-connected IR LEDs. An audio output transformer is used (in reverse) to couple audio output from TV to the IR transmitter. Transistors T1 and T2 amplify the audio signals received from TV through the audio transformer. Low-impedance output windings (lower gauge or thicker wires) are used for connection to TV side while high-impedance windings are connected to IR transmitter. This IR transmitter can be powered from a 9-volt mains adapter or battery. Red LED1 in transmitter circuit functions as a zener diode (0.65V) as well as supply-on indicator.

IR receiver uses 3-stage transistor amplifier. The first two transistors (T4 and T5) form audio signal amplifier while the third transistor T6 is used to drive a headphone. Adjust potmeter VR2 for max. clarity. Direct photo-transistor towards IR LEDs of transmitter for max. range. A 9-volt battery can be used with receiver for portable operation.




http://www.electronic-circuits-diagrams.com/audioimages/audiockt3.shtml