RFID Device Made by P89LPC903FD MCU

1 System Design
Radio frequency identification technology (RFID) has been widely used in many fields such as industrial automation, commercial automation, and transportation control and management [1]. This design is an implementation of RFID. RFID technology uses wireless radio frequency to perform non-contact bidirectional data transmission between the reader and the radio frequency card to achieve the purpose of target identification and data exchange. The radio frequency card consists of a P89LPC903FD microcontroller and a DF transmitter module, which is used to communicate with the radio frequency antenna; the reader is used to read the information of the radio frequency card, and is composed of a P89LPC903FD microcontroller, a DF super-regenerative receiver module and a filter capacitor; the reader and the radio frequency card are both powered by a 1.5 V dry battery combination, which is easy to achieve the required voltage matching; the DF transmitter module and the super-regenerative receiver module are both connected to a copper wire coupling coil. The device uses half-duplex communication to exchange information. The 8-bit rectangular pulse signal generated by the P89LPC903FD microcontroller in the reader is received by the RFID card and software-encoded, then ASK-modulated by the transmitter module. The signal is sent to the reader through the coupling coil. The coupled coil of the reader receives the signal and demodulates it through the DF super-regenerative receiving module. The decoded data is transmitted to the P89LPC903FD microcontroller through serial data transmission, and then software-decoded for data processing. The P89LPC903FD microcontroller automatically identifies the address and drives the LED to display the identification result.
2 System Implementation
2.1 Component Selection
Considering the practicality and low cost of the system, the P89LPC903FD microcontroller produced by PHILIPS is selected, and the DF transmitter module is used to implement 315MHz ASK modulation, and the DF super-regenerative receiving module is used to implement reception and demodulation [2].
The P89LPC903FD is a low-cost, low-pin, and highly integrated Flash microcontroller in a single-chip package. As shown in Figure 1, it integrates many system optimization functions and is suitable for many occasions requiring high integration and low cost. P89LPC903FD uses a high-performance processor structure. The instruction execution time is only 2 to 4 clock cycles. At the same clock frequency, its operating speed is 6 times that of the 8051 microcontroller. Therefore, a lower operating frequency is required to achieve the same working efficiency. In addition, it has low power consumption and low EMI. P89LPC903FD uses an 8-pin package. The lead pins are VDD, VSS and reset pins corresponding to pins 1, 8 and 4. All port lines have LED driving capabilities (4mA to 20mA) [3]. Its two serial ports TXD and RXD are used in this design.

2.2 System Circuit Diagram
The system circuit consists of two parts: the reader and the RFID card.
(1) Reader circuit: Connect the RXD serial port of P89LPC903FD to the DATE port of the DF super-regenerative receiving module for data reception and transmission, and implement the system function after software decoding of the received data. The VCC port is connected to a +3V DC power supply, and the specific circuit is shown in Figure 2. The module has strong temperature adaptability, stable and reliable operation, strong anti-interference ability, easy software decoding, and selects a +6V DC power supply to improve the receiving sensitivity of the receiving module, which is more practical.

(2) RF card circuit: P0.2, P0.4, P0.5, P1.1 ports are connected to the four ports of the DIP switch to complete the data input function. The input data is encoded by software and output to the TXD port of the DF transmitter module through the TXD serial port of the P89LPC903FD microcontroller to realize the transmission of RF information. The VCC port is connected to a +3V DC power supply. The power supply of the DF transmitter module can be selected from +3V to +12V power supply. The larger the selected power supply voltage, the longer the transmission distance. This design uses a +6 V DC power supply, which is easy to implement a portable power supply design. The specific circuit of the RF card is shown in Figure 3. [page]

3 Program writing and debugging
The control program is written into two P89LPC903FD microcontrollers using Keil C51. Different system baud rates are set for data transmission debugging using the serial port debugging assistant. The recognition results can reach 100%, the maximum recognition distance can reach 3 m, and the recognition time is less than 2 s.
This design uses a non-dedicated recognition chip to realize super-regenerative radio frequency identification, which is a new application of the P89LPC903FD microcontroller. The device is low in cost and power consumption, and solves the problem of high-frequency and long-distance radio frequency cards, and has high application value.