29-10-2012, 03:26 PM
ANTI-THEFT DEVICE/CHARGER FOR PORTABLE ELECTRONICS DEVICES
ANTI-THEFT DEVICE.pdf (Size: 207.39 KB / Downloads: 32)
Abstract
The electronic industry as well as the communication industry has experienced a tremendous growth over the past decades upon researches. One of the things we will like to emphasize on is the electronic charger for cell phone and portable electronics devices battery. Most of the thefts with respect to mobile phones and their misuse by other occur when these devices are on charge.
The aim of this project is to implement an electronic and communication system which we have named as “Anti-Theft Device/Charger for Portable Electronics Devices” which is aimed at solving the problem of portable device theft and misuse when they are placed on charge.
It can generate a loud chirping sound when somebody attempts to take away the mobile handset. The circuit utilizes two NE555 timer ICs: One as a simple astable multivibrator and the second as a monostable. The astable multivibrator has timing resistors but no timing capacitor as it works with stray capacitance. Its pins 6 and 2 are directly connected to a protecting shield made up of 10cm×10cmcopper-clad board. The inherent stray capacitance of the circuit is sufficient to given an output frequency of about 25 kHz with resistors. This arrangement provides greater sensitivity and enables the circuit with hand capacitance effect. Output pulses from the oscillator are directly given to trigger pin 2 of the monostable. The monostable uses a low-value capacitor, resistors and preset for timing.
The output frequency of the monostable is adjusted using the preset such that it is slightly less than that of the astable. This makes the circuit standby, when there is no hand capacitance present. The warning LED1 and buzzer are connected such that they become active only when the output of the monostable sinks current. In the standby state, the LED1 remains „off‟ and the buzzer is silent. As somebody tries to take the mobile phone from the protecting shield, his hand comes near the shield or makes contact with the shield, which introduces hand capacitance in the circuit. As a result, the astable‟s frequency changes, which makes the trigger pin of the monostable low and its output oscillates. It provides output of 6V at 180 mA through regulator IC 7806 and a resistor for charging the mobile phone (portable device).