Project

RKE Systems

RKE (Remote Keyless the Entry) system has significance for car theft, the controlling. Most of the RKE system has car’s anti-theft, alarm functions and can control the automotive, luggage door, some of which system also includes the function of remote control start or find car. A new generation of RKE may use double-sided communicate, and will be installed in the car, to control the doors. The RKE is going to be a standard configuration for a car, and to be an integral part. The biggest challenge in design RKE system is make the RKE transmitter and receiver working at low power consumption, and communications with high reliability on a long-rang. As a switch control system, it is very important on the security. Here we will introduce a RKE system with high-security. System Design RKE system is formed by transmitter, which is similar to key ring, and receiver that installed in the car. Usually operated at 315 ~ 450 MHz ISM band. Figure 1 shows a simple block diagram of the RKE system. Can be seen from the block diagram, the user presses the button on the key chain can trigger the system to wake up, and wake up the MCU inside RKE key chain, the MCU sends data stream to RF transmitters. The data stream is usually 64 to 128 bit, including a front-bit, a command code and a rolling code, using the sending rate of 2 to 20 kHz. Car RKE RF receiver to capture the RF signal and demodulate the transmitted data stream to the MCU, and MCU decode the data and send commands to the command module. Modulation for amplitude shift keying (ASK), to extend the battery life key ring.
2 Hardware Design RKE system is formed by transmitter module and receiver module. 2.1 Transmitter module The transmitter module includes buttons, MCU, RF transmitters and battery, the circuit schematic shown in Figure 2. Module powered by a 3V coin cell battery.
There are 3 buttons on the transmitter module, the functions are locked, unlock, car locator. And the 3 buttons connect to the MCU’s external interrupt, such as INT0, INT1 and INT3. MCU will be wake up and enter the corresponding interrupt handler when any button be pressed, then the system will re-enter the standby mode, 3 LEDs display the status of the three buttons. When a button pressed, the related LED will light at the same time. MCU will scan button and encode the result, sent to the transmitter data port through I/O port. The MCU control the RF transmitter U2 ENABLE pin, while enable U2's ENABLE pin, only need 250μs to make the PLL and crystal stability and emission data. U2 is a VHF / UHF base on PLL ASK / OOK type transmitter, working in 300 ~ 450 MHz band to support high-speed data transfer (100 kbps data rate), and small size, low power consumption. 2.2 Receiver module Receiver module including MCU, RF Receiver and directive implementing agencies. The RF receiver will demodulation the received OOK modulation data to original data, the MCU will decode and decryption the original data decoding to get the command, and send to the implementing agencies to execution the related operation. U3 is the RF front receiver. U3 is a low-power super-heterodyne ASK receiver, working at 300 ~ 450 MHz band, with a high sensitivity of -114 dBm, the mirror is higher than 50 dB carrier suppression. Module current in shutdown mode consumes less than 1.5μA and 5.2 mA in receive mode. The following figure shows the schematic diagram of RKE receiver module.
System coding /decoding Generally speaking, a RKE system consists of a control side (key chain transmitter module) and an execution side (receiver module in the car). Control side will control the information to be launched after coding, modulation, and receive, demodulate, decode at the execution side. The security key of RKE system is encoded. We use cryptographic techniques, which can effectively avoid the "radio listener", to improve security. The encoding and decoding process is programmed by the MCU. Encoding process shown in Figure 6 (a). The encoder detects a key input to wake the system from power saving state, the synchronization count is incremented to the formation of the cipher-text data together with the serial number, add sent with the key value and other dat. Synchronization counter value is different each time you send, even if the same button repeatedly press is no exception. Synchronization code count automatically, and no repeat. The range is 216 Hutchison value. If the other keys be pressed in the transmission process, the current sending will be terminated, but start a new transmission. Otherwise, the system will complete the send and hibernate no matter the button has been released or not. The decoding process is shown in Figure 6 (b). Corresponding to the decoder receives the data packet, de-panel the key and cipher-text separately, and the cipher key to decrypt restore the serial number and the synchronization count value, and check the serial number and the synchronization count value in accordance with the key driver the implementing agency.
Conclusion The system has obvious advantages in low power transceiver distance, reliability and security, making the RKE system to effectively control the range doubling. This RKE was system developed by us, with stable performance, low power consumption, high sensitivity, and cost advantages, the system transitions encoding capabilities, greatly improving the security.