Development of multi-function taxi pricing system

Design of a MulTI? FuncTIon Taximeter

LI Yan1, LI Xiaoyu2

(1. College of Mechanical and Electrical Engineering, Central South Un iv ersity,
Changsha 410083, China;
2.Shandong AssociaTIon of Plant Engineering, Jinan 250011, China)

Abstract: A mulTI? Function taximeter is presented in this paper, which has speech, display, measure functions and can print receipt, inquire da ta, adjust parameter and so on. The hardware circuit and software flowchart are introduced.
Keywords: taximeter; microprocessor; micro printer; IC card

1 System hardware structure and functional characteristics The system hardware block diagram of the meter is shown in Figure 1. The external signals that the system needs to input are the sensor signal and the empty car signal. The sensor is connected to the taxi shaft, and a pulse signal is sent out when the wheel rotates once, which is used to calculate the distance. The empty car light signal is used to determine whether the taxi is empty. The system uses 8052 as the central CPU unit, which is mainly divided into a voice module, a display module, a clock module, a printing module, and an IC card management module. The following introduces the various functional characteristics of the system.
1.1 The voice module takes into account the miniaturization and intelligentization of the price meter product. The voice chip adopts the ISDl420 chip with higher integration. Its biggest feature is that it uses EEPROM to directly access analog information without going through A / D and D / A conversion . It has a microphone amplifier, automatic gain control clock, speaker drive circuit, etc. It is powered by + 5V power supply.
The interface between the voice module and the main system is shown in Figure 2. The main system is connected to the ISDl420 chip through the PA port of the 8155 expansion chip. In the design process, the fixed voice part (boarding, getting off the vehicle) information is stored in different starting addresses in ISDl420. During the operation process, different voice functions can be played according to the different operating states of getting on and off the bus. When the voice chip is working, the system first transfers the main program pointer to the playback processing program, finds the pronunciation unit in ISDl420 according to the pronunciation address, and then sends the signal to the speaker to emit sound. After the main CPU completes the sound sending program, it immediately transfers to other subroutines. ?

The display module is used to display various detailed operating data during the operation of the meter, such as time, unit price, total price, waiting time and mileage. The components used are display interface chip 8279 and LED digital tube, and its interface circuit is shown in Figure 3.

This system uses the DSl2887 real-time clock chip. It has the address latch function itself, and the interface with the 8052 chip of the main system is very simple, as shown in Figure 4. AD0 ～ AD7 are bidirectional address / data multiplexing buses. AS is the address strobe input, below
After power-on, use software to initialize DSl2887, that is, write initial values ​​to each register.

Print special invoices for taxis, including license plate number, boarding time, getting off time, waiting time, operating mileage, unit price, amount and date.
This system has designed an intelligent micro-printing circuit separately: It is connected to the host by means of an interface board. This feature allows the bill printing of the meter to be functionally integrated with the main system, but can be performed separately during inspection and maintenance. The micro-printing head used in this system is the Model —— 15 0Ⅱ type printing head produced by EPSON. It is a mechanical dot matrix 4-pin printing mechanism with four horizontally mounted electromagnets on the same carriage for injection. The micro-printing uses a separate single-chip system, taking into account the performance requirements of micro-printing, using Intel's 8 051 chip. The micro-touch is connected to the main MCU through a parallel interface, and its interface diagram is shown in Figure 5. When the data to be printed appears on the printer I / O0 ~ I / O7, as long as the STB changes from high level to low level, and then from low level to high level, the data can be sent to the printer. At this time, the printer sets the BUSY line to busy (high level) and prohibits the input of new data. After the printer takes the data and processes it, the BUSY line is set to idle (low level) and sends an answer pulse ACK to notify the system. You can enter the data again. ?

This function is completed by the IC card. Some measurement parameters needed in the operation of the taximeter, such as: day and night unit price, rental mileage, rental amount, etc., are set in the IC card through the program. At the same time, the IC card is used to store the driver's detailed operation data and the IC card control settings to achieve unified management and operation data query.
In this system, the IC card is connected to the PC port of 8155. The specific connection is: the PCI port is connected to the reset terminal RST of the card socket, the PC0 port is connected to the clock terminal CLK of the card socket, the PC2 port is connected to the data input and output terminal I / O of the card socket, and the PC3 port is connected to the VDD terminal of the card socket.
The power supply of the IC card adopts the independent power supply and is controlled by 8052. When a card is inserted, it begins to provide the required power to the IC card. If you insert a bad card or metal piece that is broken by the power supply and the ground, it will cause a short circuit in the power supply circuit and interfere with the operation of the entire device. Using IC card independent power supply mode, when the IC card power supply short circuit occurs, the power regulator forms a short circuit protection due to output overload, and the output is low. When the CPU detects a low level, the power supply to the IC card is interrupted. ?

The system software adopts modular design, and the system program is solidified in the internal ROM of the single chip microcomputer. The block diagram of the main program is shown in Figure 6, which contains several subroutines and interrupt service routines. The functions of the subroutine include system initialization, key processing, display, voice and data transmission processing, etc. The interrupt service program includes counting and processing of driving pulses, counting and processing of time, power-off protection processing, printer processing, etc.

The price meter realizes automatic control of IC card measurement parameters and double backup of key data, which greatly improves the accuracy and stability of driving data. In addition, the meter is composed of high-reliability components and devices, with a variety of anti-interference measures, which can withstand the test of various harsh conditions. The new multi-function meter system has stable performance, small size and low cost, and can well meet the market requirements for taxi meter. ?