出租車計(jì)價(jià)器畢業(yè)設(shè)計(jì)中英文翻譯(文件)
【正文】 ith different diving ratios. A Possible circuit diagram is shown in figure 7. It consists, in this case, of three decade counter type 7490, two 3input AND, one 5input AND, one 2input AND one 3input OR gates. D. Circuit CT4 Which Generates Clock Pulses for Display Circuit The function of this circuit is to supply one, two or three pulses at the output terminal R for each pulse generated at any 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 counter type 7493, one half of a dual JK masterslave flipflops circuit type 7476, three inverters, three 2input AND, one 3input AND, one 2input OR and one 3input 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 flipflop. 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 to reset the counter and change the state of the flipflopsuch that Q bees , 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 flipflop should be cleared whenever a new channel is operated. This has been achieved by the input 5 and will be explained later when describing the function of the channels rotary selector switchs. E. Display Circuit As shown in Figure 2, the display panel would contain three 4digit displays that give the sum of money required from each passenger separately as well as a one sixdigit display that gives the total ine 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 and 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 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 sum display will be enabled whenever any of the three displays is enabled (this is done by a 3input 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 Fares In the following part, two different methods for changing over between time andistance fares are 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 (Table 2) can show that time fare should be used whenever the taxicab moves with speed less than 50 m/min. A possible circuit 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 2input 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 second 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 should be supplied by the terminals of the rotary selector switches in order to ensure proper operation by the electronic circuit are given
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