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1、精选优质文档-倾情为你奉上ABSTRACT1. INTRODUCTIONTransporting people in the morning from their homes to their works and back in the afternoon has become a big problem in big cities especially in undeveloped countries. As a partial solution of this problem, the authorities in some countries had, unofficially, lef
2、t the taxicab drivers to carry different passengers to different places at the Same time. For example, a taxicab with four seats may carry four different passengers without any relation between them except that their way of travelling is the same.Accordingly, it has become very difficult to rely on
3、the present conventional single-channel taximeter to determine the fare required from each passenger separately. Accordingly, an unfair financial relation was created between the taxicab driver, owner, passengers and the state taxation department.Under these circumstances, taxicab drivers force the
4、passengers to pay more than what they should pay. In some cases passengers had to pay double fare they should pay. With the present conventional single-channel taximeter, taxicab owners are not able to determine the daily income of their taxicab.In some cases (a taxicab with four seats) they may onl
5、y get one quarter of the income of the taxicab (collected by the taxicab driver). From which they should pay 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
6、 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
7、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
8、 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
9、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 di
10、stance 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
11、 also included. A prototype has been built under grant from the Egyptian Academy for Scientific and Technological Research.2. AN EXPERIMENTAL THREECHANNEL TAXIMETERTheory of operation of our experimental device to work as an electronic digital taximeter is based on t h e fact thathe speedometer cabl
12、e 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, o
13、ur 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 number of passengers hiring the taxicab. The device may be splitted
14、 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
15、 of both the driver and the passengers.A possible components locations is shown in Figure 1.A. Speed Sensor UnitThe 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
16、 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 gene
17、rator 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 tax
18、icab 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 anddisplay unit is shown in Figure 3. The control and display panel contains all controls nece
19、ssary 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.
20、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 a
21、nd 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 and third passengers, respectively.Pushing the total sum pushbutton 4 unblanks the fourth readout enabling any person to retain
22、 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 CIRCUITThe general block dia
23、gram 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 whi
24、ch generates clock pulses for the display circuit.A. Number of Passengers Detection Circuit CT1 As shown from the general block diagram, the circuit CTI has three inputs I, 2 and 3 as well as three outputs J, K and L. The function of the circuit is to supply a high level voltage at terminals J, K or
25、 L if and only if one, two or three passengers are hiring the taxicab, respectively. The term passenger, here, means one person or a group of related persons. When a passenger is getting into the cab, we simply turn on a free readout display by turning the corresponding rotary selector switch to a f
26、ully clockwise direction.This will automatically disconnect the corresponding terminal I, 2 or 3 from ground. The logical relation between various input terminals I, 2 and 3 and the output terminals J, K and L is shown in Table 1.As a combinational circuit we start the design by deriving a set of bo
27、olean functions. A possible simplified boolean functions that gives minimum number of inputs to gates may be obtained from Table I.A possible logical diagram that is based on the above derived expressions is shown in Figure 5.It consists of two inverters, four 2-input AND, to3-input AND two 3-input
28、OR gates B. Tavelling Distance Scaling Circuit CT2As shown from the block diagram of Figure 4, the circuit CT2 has four input J, K, L and E and one output M. The function of the circuit is to supply a single pulse at the output M for a certain number of pulses generated at the output of the speed se
29、nsor (certain number of meters travelled by the taxicab), according to the number of passengers hiring the car. A suggested fare per kilometer of travelling distance is shown in colomn two of Table 2. the circuit, in this case, should supply a single pulse at the output M for every 100, 125 or 143 p
30、ulses generated at the input terminal Eaccording to the level of voltage at input terminale 3, K or L, respectively.Our circuit could be, as shown in Figure 5, three decade counters, connected as a three digit frequency divider whose dividing ratios 100, 125 and 143 are automatically selected by the
31、 voltage level at terminals J, K and L, respectively.A possible circuit diagram that may verify the above function is shown in Figure 6. It consists of three decade counters type 7490, one BCD-to decimal decoder type 7445, three 4-input AND, one 3-input ANDone 2-input AND two 3-input OR gates.C. Tim
32、e Scaling Circuit CT3As shown in the block diagram, the time scalingcircuit will have four inputs J, K, L and F and one output N. The function of this circuit and accordingto colomn three of Table 2 (fare per 2 minuts of waiting time) is to supply a single pulse at the output N for every 120, 240 or
33、 360 pulses supplied at the input terminal F from the I Hz clock according to level of voltage at inputs J, K and L, respectively.Time scaling circuit would be similar to the distance scaling circuit but with different diving ratios. A Possible circuit diagram is shown in figure 7.It consists, in th
34、is case, of three decade counter type 7490, two 3-input AND, one 5-input AND, one 2-input AND one 3-input OR gates.D. Circuit CT4 Which Generates Clock Pulses for Display CircuitThe function of this circuit is to supply one, two or three pulses at the output terminal R for each pulse generated at an
35、y of the terminals N or M, according to the voltage level at the input terminals J, K or L, respectively. The output P will receive a pulse for each pulse generated at any of the input terminals N or M. This function can be performed by the circuit shown in Figure 8, it consists of one ripple counte
36、r type 7493, one half of a dual JK masterslave flip-flops circuit type 7476, three inverters, three 2-input AND, one 3-input AND, one 2-input OR and one 3-input OR gates. When a pulse is generated at either input terminals N or M, a high level voltage will be generated at the output Q of the flip-fl
37、op. This will g a t e t h e I Khz signal to be connected to the input A of the ripple counter as well as to the output terminal R. When one, two or three pulses are counted by the ripple counter, according to the level of voltage at the input terminals J, K and L, respectively, a high is generated t
38、o reset the counter and change the state of the flip-flopsuch that Q becomes low.Hence, the 1 KHz signal is disabled to reach the outputerminal R or the input A of the ripple counter. In order to ensure the proper function of the circuit, the flip-flop should be cleared whenever a new channel is ope
39、rated. This has been achieved by the input 5 and will be explained later when describingthe function of the channels rotary selector switchs.E. Display CircuitAs shown in Figure 2, the display panel would contain three 4-digit displays that give the sum of money required from each passenger separate
40、ly as well as a one six-digit display that gives the total income of the taxicab. A possible wiring diagram for the display circuit is shown in Figure 9. Rotating any of the rotary selector switches to fully clockwise direction will supply the corresponding display by5 volts through terminals 1, 2 a
41、nd 3, respectively.The corresponding display will be unblanked by supplying a low level of voltage through terminals A, C and G, respectively. Keeping terminals 8, D and H, respectively, at low level will keep them reset to zero. The corresponding display is then enabled by removing the low voltage
42、from terminals B, D, and H, respectively, to be ready for counting the sum of money required from the corresponding passenger starting from zero.The counting pulses for these three displays are supplied through terminal P. The total sumdisplay will be enabled whenever any of the three displays is en
43、abled (this is done by a 3-input OR gate as shown in Figure 8). Retaining the contents of the last display will be done by unblanking it by supplying a low level of voltage to terminal I as shown in Figure 10 b.F. Changing Over Between Time and Distance FaresIn the following part, two different meth
44、ods for changing over between time andistance faresare suggested:The first is to switch to time fare whenever the distance fare is less than the time fare. Hence,a simple look to fares table can show that time fare should be used whenever the taxicab moves with speed less than 50 m/min. A possible c
45、ircuit that can perform this switching action is shown in Figure IO c. It contains one rpm limit switch and a one inverter as well as two 2-input AND gates.The contacts of the limit switch are normally closed and will be opened whenever the angular speed of the speedometer cablexceeds 50 rmp. The se
46、cond alternation is to connect the input of the inverter in Figure 10 c. to the output terminal Q of the speedometer circuit, Figure 2.In this case, the switching into time fare will be done whenever the taxicab is at stand still.G. Function of the Rotary Selector Switches The voltage levels that sh
47、ould be supplied by the terminals of the rotary selector switches in order to ensure proper operation by the electronic circuit are given in Table 3. Connection of three rotary selector switches each witb four decks of five poles each, that satisfy the logic function of Table 3, is shown in Figure 1
48、0 a. Rotating any of the three switches into fully clockwise direction will pass through five positions. The function of the rotary selector switches can be described starting from the first position passing through variousteps until reaching the final position as follows:Initial position: In this p
49、osition a low voltage level is applied to terminals I, 2 and 3, this will disconnect the 5 volts supply from the three first displays, set the three inputs of the number of passenger detection circuit CTI to low level. A low voltage level is applied to terminals 8, D and H, this is to ensure that the total income display is disabled.Voltage levels at terminals A, C, G and S are at no care condition.Step I: Rotating any of the rotary selector switches one step toward