At present, most domestic expressways and expressways adopt the semi-automatic toll collection method of manual toll collection and computer-aided management, which greatly reduces the traffic capacity and service level of expressways, but there are also many deficiencies and disadvantages, such as unsupervised toll collection, large leakage holes, inconsistent vehicles and cards, and some vehicles may illegally evade tickets. In order to solve these problems, To meet the needs of market development, China has begun to try to use the rapidly rising electronic toll collection (etc) in the world. In etc, when the vehicle passes through the toll station, the automatic vehicle identification technology is used to automatically complete the wireless data communication between the vehicle and the toll station, carry out the automatic vehicle identification and the exchange of relevant charging data, and process the charging data through the computer network, so as to realize the automatic charging without stopping. Due to the high speed and high efficiency of electronic data processing, So as to speed up the speed of vehicle traffic, effectively alleviate the possible congestion of roads and bridges, and combined with the network transmission of data information, make the unified management of vehicle charging more simple and easy. Although the movement of non-stop toll collection system abroad is very successful and has certain characteristics, some technical characteristics and operation methods are not suitable for China’s national conditions, which are embodied in the following aspects:
The cost of the system is relatively high;
The system works in 915MHz frequency band, which is allocated to mobile communication in China, and is inconsistent with the 5.8GHz table standard to be adopted by the state;
The vehicle still needs to slow down properly when passing the toll point.
The vehicle charging system designed in this paper can effectively solve the above problems, realize the real non-stop charging, greatly shorten the charging time and high vehicle flow rate; The unified currency settlement combined with the management information center basically eliminates the loss of funds and reduces the system cost, which is conducive to the promotion of non-stop charging system in China.
2. Composition of charging system
The electronic toll collection system is mainly composed of wireless transmitter, wireless receiver and management information center. As shown in Figure 1, the mobile vehicle is selected to install the receiver in the system design, because if the vehicle is used as the transmitter, the transmitted information is very similar to the information to be fed back by the receiver, The aircraft is prone to information conflicts and unrecognizable contradictions. Considering that the information actually obtained by each vehicle is the same, the transmitter is flexibly installed with fixed objects, fixed on both sides of the road, and circularly transmits the same information. When the receiver installed on the vehicle enters the effective sensing area of the transmitter, the receiver receives the signal of the transmitter, And store the data after corresponding processing. At the same time, judge whether the alarm reminder is needed through the monitoring program; The transmitter and receiver can also communicate with the management information center through the computer. The center uniformly adjusts the charging information of the transmitter. The receiver cooperates with the center for actual currency settlement, and updates the data for user query and overall management of the center.
3. Wireless communication module and hardware design
In this design, according to the specific design requirements, et13x210 / et13x221 RF transmitter and receiver of Taiwan etorns company are selected to realize the wireless communication function.
3.1 et13x210 and et13x221
Et13x221 transmitter integrates phase-locked loop, channel selector and transmission buffer. Et13x210 receiver integrates PLL, mixer, if amplifier, filter, demodulator and channel selector. Its structure diagram is shown in Fig. 2 and Fig. 3 respectively. The circuit has the following characteristics:
The on-chip phase-locked loop technology is used and the 4MHz crystal oscillator can be connected externally. The working frequency is accurate and very stable. The center frequency is 27MHz. There are 10 channels to choose from. The interval of each channel is 30MHz to ensure that multiple modules do not interfere with each other during point-to-point transmission;
Using frequency shift keying modulation, the structure is simple, practical and has more anti-interference ability than amplitude modulation;
Low power consumption, the maximum working current in standby mode is only 10 μ A；
The transmission power is 0dbm-3dbm, equipped with appropriate antenna, and the stable transmission distance is up to 10m.
With et13x221 / et13x210 as the core and some peripheral analog circuits, a wireless communication module can be formed.
3.2 circuit design of wireless communication transmitting module
The hardware circuit of the transmitting module based on et13x221 is shown in Figure 4.
The data to be transmitted is input from the data in terminal. The input of this terminal is a digital signal. After the signal is input, it passes through the LC oscillation circuit, uses the signal output from the phase test to feed back to the voltage controlled oscillator (VCO) in the control circuit to stabilize the clock frequency, selects the channel by the BCD coding mode of the external switch, and generates a high-frequency carrier near 27MHz, The baseband signal is added in the form of FSK, and then transmitted by the antenna through the filter and amplification circuit. The hardware circuit of the receiving module based on et13x210 is shown in Fig. 5.
The signal received through the antenna is first sent to the input circuit of RF mixing, and the output signal of rfin module is input to the mixer inside the circuit. At the same time, in order to avoid the interference of similar frequencies on the main frequency, the intermediate frequency filter is used to attenuate the frequency close to the main frequency, so that the reception of the main frequency can work normally, and then the original signal is output through the demodulation and decoding circuit, The data OP terminal is sent to the microprocessor for control processing.
4. Software design
The application software of remote control vehicle toll station is mainly composed of transmitting and receiving parts, which basically realizes the functions required by the system design, and the software uses structured programming to facilitate reading, writing, modification and secondary development.
4.1 transmitting module
According to the communication protocol, the relevant information is packaged and sent to the transmitter in a certain format, and then the information is circularly transmitted through the transmitter. The module is mainly composed of data coding subroutine and data transmission subroutine.
4.2 receiving module
When the receiver receives the signal, it shall check the header information according to the communication protocol to determine the start of communication, receive the complete information packet from the header, and decode and detect the error of the received information. If the received information is found to be wrong after detection, it shall be received again until the received information is completely correct, and then judge whether it is allowed to receive the information again according to the design principle.
Through experimental verification, the wireless communication module of the system can correctly transmit and receive information, the designed non-stop automatic toll collection system runs stably, the vehicle can correctly charge automatically in a limited area, and there is no need to slow down in the charging process, so as to realize barrier free and non-stop charging in the real sense.
Responsible editor: GT