【正文】 ated. 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 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 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 10 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 position 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 ine 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 clockwise direction will supply 5 volts to the corresponding display, provides a high level voltage at terminals 1, 2 or 3 indicating that one passenger have entered the taxicab. A high level voltage should be applied to terminals A, C or G in order to ensure that the corresponding display is still blanked. Other terminals B, D, H and S are kept unchanged. Step 2: Rotating the rotary selector switch one step further, will change the state of voltages at terminal A, C or G to be at low level and unblanks the corresponding display. States of voltages a