Design scheme of new computer anti-theft system

introduction

Bluetooth is an open short-range wireless communication technology specification that works in the global 2.4GHz ISM band. The data rate of Bluetooth is 1Mb / s. Frequency hopping is performed at the rate of 1 600 hops / s on the globally open 2.45GHz ISM frequency band. The 2.4GHz ISM frequency band is used without applying for a license. Bluetooth itself has the characteristics of good confidentiality, strong anti-interference ability, low power consumption, and easy integration, especially its codec is consistent. At present, Bluetooth technology has matured in the world, and its short-distance transmission and modularization have greatly helped our design.

This design uses Bluetooth technology for computer anti-theft . Bluetooth technology is used to detect whether the protected computer is within a safe range. When the protected computer is stolen, the Bluetooth receiver detects that the computer is out of the safe range, and activates the alarm to alarm, thereby playing the role of computer anti-theft.

1 System hardware scheme design

Hardware Design Overview The hardware design of this system is mainly divided into two parts:

â‘  Bluetooth signal generating part; â‘¡ Bluetooth signal receiving and processing part.

The signal generator is carried by the user, and it transmits a Bluetooth detection signal to the signal receiver.

Due to its small size, the signal receiving part can be integrated into the computer to detect whether the computer is within the specified range and decide whether to alarm.

The signal generation part of this system uses the 555 timer to realize the second pulse working mode. Let the transmitting part send the Bluetooth signal in a cycle of one second, and fully reduce the power consumption.

When the distance between the user's computer and the signal generator is within the specified range (10 m in this system), the Bluetooth receiver can receive the Bluetooth signal, indicating that the computer is safe and the microcontroller does not enable the alarm operation.

When the user's computer exceeds the specified range, the Bluetooth receiver cannot receive the Bluetooth signal, indicating that the computer is stolen and the microcontroller enables the alarm operation.

The signal generation part includes a power supply module, a signal generation module, and a 555 timer module.

The signal receiving part includes a power supply module, a signal receiving module, a microcontroller module, and an alarm module. The hardware schematic diagram is shown in Figure 1.

Hardware schematic

2 Hardware design

2.1 555 timer module

The 555 timer is a medium-sized integrated device that combines analog and digital functions. The 555 timer has a wide power supply voltage range and can work from 4.5V to 16V with reliable performance. Only a few external resistors and capacitors are needed to realize pulse generation and conversion circuits such as multivibrator, monostable trigger and Schmitt trigger. Its internal circuit is shown in Figure 2.

555 timer internal circuit

The working principle of the 555 timer is as follows: when the input signal is input from pin 1 and exceeds 2VCC / 3, the flip-flop is reset, the output pin 3 outputs a low level, and at the same time discharges, the switch is turned on; when the input signal is input from pin 2 When it is lower than VCC / 3, the flip-flop is set, pin 3 outputs high level, and discharges at the same time.

2.2 Transmitter power supply

The power supply of the transmitting module includes a lithium battery, a charging circuit and a voltage stabilizing filter circuit, which provides a 3.3V working voltage for the Bluetooth signal generating module. The 5V voltage of the USB interface of the computer can easily charge the lithium battery, and the anti-overcharge and over-discharge circuit can work the lithium battery in the best state. When an external USB power source is connected, it supplies power to the Bluetooth signal generation module and simultaneously charges the lithium battery; when there is no external power source, the lithium battery supplies power to the Bluetooth signal generation module. Select the LDO (Low Dropout Linear Regulator) chip SPX1117-3.3 of Sipex Company to stabilize the output voltage at 3.3V.

Power module

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