【文章內(nèi)容簡(jiǎn)介】 introduced a multichannel taximeter that can deal with more than one passenger t should be pointed out that by the term passenger we mean a one person or a group of related t should also be pointed out that our proposed multichannel taximeter is not, simply, a multi display a matter of fact it contains logic circuits that automatically changes the fare per killometer of travelling distance or per minutes of 39。waiting time according to the number of passengers hiring the the following part and as an example, we will present a plete design for a threechannel diagrams as well as detailed circuit diagrams of the experimental threechannel taximeter are also prototype has been built under grant from the Egyptian Academy for Scientific and Technological 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 , 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 , our experimental taximeter is not simply a three display 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 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 second unit contains the main electronic circuit, the displayand control unit should be located somewhere in front of both the driver and the possible ponents locations is shown in Figure Sensor Unit The main function of this unit is to supply train of pulses whose frequency is proportional to the angular rotation of the possible form of a speed sensor is shown in Figure may consist of a 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 output voltage at terminal Q is then limited to the value of volts by using a Ik ohms resistor as well as a zener diode level of the voltage at terminal Q would be high whenever the taxicab is moving and will be zero voltage can be used for the automatic switching from distance fare to time Electronic and Display Unit A suggested shape for the main electronic and display unit is shown in Figure control and display panel contains all 39。 controls necessary for operating the taximeter as well as four readout 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, fourth readout will give the total ine of the contents of the last readout should be nonvolatile and be able to be retained even during parking the channel rotary selector switchs 1 , 2 and 3 have fully clockwise/anticlockwise the fully anticlockwise position, the counter of the corresponding readout is blancked and 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, the total sum pushbutton 4 unblanks the fourth readout enabling any person to retain the readout corresponding to the total the release of the pushbutton, the fourth readout will be blanked unit also contains the main electronic circuit which will be fully described in the following OF THE MAIN ELECTRONIC CIRCUIT The general block diagram of the main electronic circuit is shown in Figure 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 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 function of the circuit is to supply a high level voltage at terminals J, K or L if and only if one, two or three passengers are hiring the taxicab, term passenger, here, means one person or a group of related a passenger is getting into the cab, we simply turn on a free readout display by turning the corresponding rotary selector switch to a fully clockwise will automatically disconnect the corresponding terminal I, 2 or 3 from logical relation between various input terminals I, 2 and 3 and the output terminals J, K and L is shown in Table a binational circuit we start the design by deriving a set of boolean possible simplified boolean functions that gives minimum number of inputs to gates may be obtained from Table possible logical diagram that is based on the above derived expressions is shown in Figure consists of two inverters, four 2input AND, to3input AND two 3input OR gates Distance Scaling Circuit CT2 As shown from the block diagram of Figure 4, the circuit CT2 has four input J, K, L and E and one output 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 sensor(certain number of meters travelled by the taxicab), according to the number of passengers hiring the suggested fare per kilometer of travelling distance is shown in colomn two of Table circuit, in this case, should supply a single pulse at the output M for every 100, 125 or 143 pulses generated at the input terminal E according to the level of voltage at input terminale 3, K or L, circuit could be, as