希洛·尤尔的基于VHDL的计程车计价器设计(13)

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重庆邮电大学本科毕业设计（论文）

the salary of the taxicab driver as well as the cost of fuel, minor and major repairs in addition to the car depreciation. As a matter of fact the position of the taxicab owners is not so bad as it seems. A general agreement has been reached between the taxicab drivers and owners such that the drivers should guarantee a fixed daily income to the owners as well as the paying for the cost of fuel as well as the minor repaires. Even though the taxicab drivers still share the large portion ofthe income of the taxicab. Also with the presence of the single-channel taximeter, it has become very difficult for the state taxation department to know the yearly income of the taxicab and accordingly it has become very difficult to estimate the taxes to be paid by the taxicab owners.

In order to face this problem, the state taxation department had to impose a fixed estimated taxes for each seat of the taxicab whatever the income of the taxicab. In this paper, we introduced a multichannel taximeter that can deal with more than one passenger simultaneously. I t should be pointed out that by the term passenger we mean a one person or a group of related persons. I t should also be pointed out that our proposed multi-channel taximeter is not, simply, a multi display readouts. As a matter of fact it contains logic circuits that automatically changes the fare per killometer of travelling distance or per minutes of 'waiting time according to the number of passengers hiring the taxicab. In the following part and as an example, we will present a complete design for a three-channel taximeter. Block diagrams as well as detailed circuit diagrams of the experimental three-channel taximeter are also included. A prototype has been built under grant from the Egyptian Academy for Scientific and Technological Research. 2. AN EXPERIMENTAL THREECHANNEL TAXIMETER

Theory of operation of our experimental device to work as an electronic digital taximeter is based on t h e fact thathe speedometer cable rotates one revolution for each meter of travelling distance.

Accordingly, if the speedometer cable is coupled with a speed sensor that generates a single pulse for each meter of travelling distance, then our taximeter could be three up counter modules associated with a speed sensor unit.

However, our experimental taximeter is not simply a three display readouts. As a matter offact it contains logic circuits that automatically changes the fare per kilometer of travelling distance or per minutes of waiting time according to the

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重庆邮电大学本科毕业设计（论文）

number of passengers hiring the taxicab. The device may be splitted into two main parts: The first is the speed sensor unit which may be located anywhere in the taxicab such that an easy coupling to the speedometer cable can be achieved. The second unit contains the main electronic circuit, the displayand control panel. The unit should be located somewhere in front of both the driver and the passengers. A possible components locations is shown in Figure 1. A. Speed Sensor Unit

The main function of this unit is to supply train of pulses whose frequency is proportional to the angular rotation of the wheels. A possible form of a speed sensor is shown in Figure 2.

If may consist of a tj.pica1 permanent magnet sine wave generator with its output connected to a pulse shapping circuit (two general purpose silicon diodes, 1K ohms resistor and a schmit trigger inverter).

In order to find some way to detect the movement of the taxicab, the output of the sine wave generator is rectified through a general purpose silicon diode Dl then smoothed by a 1000 F capacitor. The output voltage at terminal Q is then limited to the value of 4.7 volts by using a Ik ohms resistor as well as a zener diode ZD. The level of the voltage at terminal Q would be high whenever the taxicab is moving and will be zero otherwise. This voltage can be used for the automatic switching from distance fare to time fare.

B. Main Electronic and Display Unit A suggested shape for the main electronic and

display unit is shown in Figure 3. The control and display panel contains all ' controls necessary for operating the taximeter as well as four readout displays. The first channel will give the sum of money required from the first passenger, while the second and third readouts are for the second and third passengers, respectively. The fourth readout will give the total income of the taxicab.

The contents of the last readout should be nonvolatile and be able to be retained even during parking the taxicab. The channel rotary selector switchs 1 , 2 and 3 have fully clockwise/anticlockwise positions. In the fully anticlockwise position, the counter of the corresponding readout is blancked and disabled.

In the fully clockwise position, the counter is unblanked, cleared to zero and enabled to be ready for counting the sum of money required from the first, second

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重庆邮电大学本科毕业设计（论文）

and third passengers, respectively.

Pushing the total sum pushbutton 4 unblanks the fourth readout enabling any person to retain the readout corresponding to the total income. After the release of the pushbutton, the fourth readout will be blanked again. This unit also contains the main electronic circuit which will be fully described in the following section. 3. DESCRIBTION OF THE MAIN ELECTRONIC CIRCUIT

The general block diagram of the main electronic circuit is shown in Figure 4. It consists of five subcircuits designated by the symboles CTI up to CT4supporting circuits, these are: The number of passenger deticition circuit CTI, travelling distance scaling circuit CT2, waiting time scaling circuit CT3, circuit CT4 which generates clock pulses for the display circuit.

A. Number of Passengers Detection Circuit CT1 As shown f …… 此处隐藏：5376字，全部文档内容请下载后查看。喜欢就下载吧 ……