Design of Intelligent Anti-Stealing System Based on LPC2132

“With the continuous development of computer technology and communication technology, the Internet and embedded intelligent instruments have become more and more widely used. Its appearance provides strong technical support for the distributed control system to realize real-time and reliable data communication between nodes. It is a serial communication network that effectively supports distributed control or real-time control. The article analyzes the design of an intelligent anti-theft system based on LPC2132.

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0 Preface

With the continuous development of computer technology and communication technology, the Internet and embedded intelligent instruments have become more and more widely used. Its appearance provides strong technical support for the distributed control system to realize real-time and reliable data communication between nodes. It is a serial communication network that effectively supports distributed control or real-time control. The article analyzes the design of an intelligent anti-theft system based on LPC2132.

1 Overall hardware design scheme

Based on the above-mentioned functional planning of the device, the device design can be divided into two parts. The intelligent monitoring system is composed of two parts: the upper computer and the lower computer. The upper computer is realized by the PC. The lower computer includes a master single-chip microcomputer composed of MSP430F149, a 4×4 human-machine interface keyboard, a relay control circuit, and an acousto-optic alarm circuit.

1.1 Sensor selection

1.1.1 Power metering chip selection

The electricity collection part mainly realizes the collection and storage of electricity through the energy metering chip AD7755. A day can be divided into 48 time periods, that is, one time period every half an hour. The single-chip microcomputer sends the number of pulses collected in half an hour and the maximum power value collected in half an hour to the database server, and then the database The server realizes real-time data updates and publishes them in the form of dynamic web pages. The electric quantity sampling circuit is the key circuit of electric energy measurement, as shown in Figure 1.

Figure 1 Electric energy sampling circuit

1.1.2 Selection of oil temperature sensor

Using platinum resistance as the sensor for transformer oil temperature measurement, the temperature measurement circuit is shown in Figure 2. The oil temperature sensor is used to measure the oil temperature of the transformer. When the oil temperature is higher than the set value, it will alarm and cut off the transformer switch.

Figure 2 Temperature measurement circuit

The parameters are as follows:

①Measuring range: -200℃～+850℃; ②Allowable deviation △℃: Class A ±(0.15+0.002│t│), Class B ±(0.30+0.005│t│); ③Minimum insertion depth: heat The minimum insertion depth of the resistor is ≥200 mm; ④The let-through current is ≤5 mA.

1.1.3 Selection of oil level sensor

Use UZF2 (side-mounted) remote transmission type turning column control level gauge. The magnetic turning-column level gauge is a device specially developed for liquid level measurement based on the principle of magnetism, Archimedes (law of buoyancy) and other principles ingeniously combined with the characteristics of mechanical transmission. The control type is the liquid-level measurement device. On the basis of the level gauge, a magnetic control switch is added. While monitoring the liquid level, the magnetic control switch signal can be used to control or alarm the liquid level; the remote transmission type is based on the column-turning liquid level gauge with an increase of 4-20mA. Send sensor, while monitoring the liquid level on site, transmit the change of liquid level to the control room through the transmitter sensor, cable and instrument to realize remote monitoring and control.

1.1.4 Selection of anti-theft signal

After the whole system is powered on, the main control system and the microcontroller start self-checking. After the initialization is completed, if the remote management center does not receive the command sent by the GPRS, the main system will measure and control the current and monitoring data of the meter in sequence, and measure the transformer. The oil temperature and oil level are processed together to determine whether the metering box door is normal. The measurement and monitoring data sent by the measurement and control subsystem are regularly received, and the data processing and output control are performed. At the same time, the measurement and control subsystem sequentially measures the current and the high-voltage magnetic sleeve. Oil temperature, and monitor the status and oil level of the positioning electromagnet in the high-voltage magnetic sleeve. When the main measurement and control system receives the command sent by the remote management center via GPRS, it will judge the command to determine whether it is the closing or disconnecting command of the load switch inside the transformer, or the positioning or releasing command of the electromagnet in the magnetic sleeve and the door of the metering box. Positioning electromagnet positioning or release instructions. The main measurement and control system sends the corresponding instruction content to the measurement and control subsystem and outputs control to complete various functions. In addition, the main measurement and control system forms two curves on the LCD and stores the measured current value and the current value read from the meter in real time. The control circuit mainly realizes the control of the positioning electromagnet in the metering box. The positioning electromagnet mainly realizes the locking control of the metering box door. When the positive direction of the positioning electromagnet coil is energized, the positioning bolt of the electromagnet locks the metering box door. When the direction is energized, the positioning bolt of the electromagnet is released, and the metering box door can be opened. Figure 3 is the circuit diagram of the output control electromagnet.

When PTC3 and PTF6 are both at high level, the positive direction of the solenoid coil is energized to lock the metering box door and cannot be opened. When it needs to be opened, make PTF7 and PTC0 both high, release the electromagnet, and the metering box door can be opened.

Figure 3 Circuit of output control electromagnet[page]

1.2 Single-chip selection

The design adopts the LPC2132 chip of PHILIPS company based on the ARM architecture as the MCU of the data acquisition terminal. The LP C2132 microcontroller is based on a 32-bit ARM7TDMI-SCPU that supports real-time simulation and embedded tracking, and has a 64 kB high-speed Flash memory.

The 128-bit wide memory interface and unique acceleration structure enable 32-bit code to run at the maximum clock rate. The remote data acquisition system is connected to the Ethernet through the network interface module, and the remote computer sends task requests or the acquisition system actively transmits data to the remote monitoring computer to realize the interconnection between the equipment and the Internet.

1.3 The choice of network interface chip

The design adopts the 28-pin independent Ethernet controller ENC28J60 introduced by Microchip Technology; adopts the EIA/568A wiring standard of RJ45 connector network cable, and uses eight-core twisted pair as the transmission medium, with RJ45 connector as the interface .
The design of the network interface circuit is based on the functions, timing and logic levels of LPC2132 and ENC28J60. The network interface circuit is shown in Figure 4.

Figure 4 Network interface circuit

1.4 Serial bus interface

LP C2132 has two UART serial interface modules, which can be easily connected with serial devices. In the design, UART0 is used as the RS232 interface, and UARTI is used as the RS485 interface. RS232 is mainly used for system debugging, and can also be connected with equipment using RS232 communication. RS485 is used as the input and output channel of the gateway.

1.4.1 RS-232 conversion circuit

The design uses SP3232E chip. It can convert the input level to a standard TTL level (for MCU), and it can also convert the input TTL level to a negative logic level (for PC). Its working circuit is shown as in Fig. 5.

Figure 5 SP3232E circuit

1.4.2 RS485 interface circuit

The design uses Sipex’s low-voltage RS485 interface chip SP3481, which only needs a +3.3 V power supply to generate the 1.5 V differential output required by the differential output. SP348lE works in half-duplex mode. The chip includes a driver and a receiver, and there are 8 external pins.

The R/D signal output by the LPC2132 directly controls the SP3481 chip’s transmitter/receiver enable: R/D signal is “1”, the SP3481 chip’s transmitter is valid, and the receiver is disabled. At this time, LPC2132 can send to the RS485 bus Data byte: The R/D signal is “0”, the transmitter of the SP3481 chip is disabled and the receiver is valid. At this time, LPC2132 can receive data bytes from the RS-485 bus. As shown in Figure 6. In this circuit, only one of the “receiver” and “transmitter” in the SP3481 chip can be in operation at any time.

Figure 6 RS-485 circuit connection

2 Conclusion

With the widespread application of Electronic technology, intelligent anti-theft control technology is bound to become a development trend. The article proposes to use gateways and new sensors to test transformer parameters. The debugging results show that the system is highly reliable and easy to use. The anti-theft intelligent system established by the above method has the characteristics of simple wiring, stable system controller, and high data transmission reliability. It has achieved good results in actual use. Has a certain promotion significance.