Taximeters

#This invention relates to taximeters.

#In the past taximeters have been provided incorporating mechanical linkages and gear trains to provide a visual representation of a fare for a taxi hireage proportional to some predetermined combination of the distance travelled and the time taken. Such taximeters are subject to the normal limitations of wear and servicing requirements of mechanical appliances, and also involve considerable difficulty and expense to change the apparatus when changes are made in taxi hireage tariffs, which changes are at present frequently required.

#It is therefore an object of the present invention to provide a taximeter which will obviate or minimise the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.

#To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

#The invention consists in the foregoing and also envisages constructions of which the following gives examples only.

#One preferred form of the invention will now be described with reference to the accompanying drawings in which:

#In the preferred form of the invention a sensor unit 1 is provided consisting of a sensitive pickup coil 2, a very high gain amplifier 3 and a trigger circuit 4. When the pickup coil is in a varying magnetic field, a minute current flows. This current is amplified and integrated over the complete cycle of variation thus reducing the sensitivity to noise and short sharp changes. The amplifier signal is then applied to the trigger circuit where it is converted to clean sharp pulses. These pulses are then applied to the meter. When the sensor unit is located close to a vehicles speedmoter it picks up the rotating magnetic field which is actually generated within the speedo. This produces a distance pulse train having one pulse per revolution of the speedo cable at sensor output 6.

#Alternatively the sensor could consist of a transducer (not shown) consisting of a permanent magnet, a reed switch and a slotted vane connected to the drive train of the taxi so that the slotted vane rotates within the magnetic field to open and close the reed switch to create a similar distance pulse train.

#The pulse train, having a frequency proportional to the speed of the taxi, is fed into a monostable 7 which triggers on both edges of the input signal thus giving two pulses per revolution and the resulting output fed into a calibration rate divider 8. As the number of pulses per kilometer is dependent on the car type and model this must be normalised to the meter standard and this is done by the calibration divider. A fixed pulse rate, for example 1200 pulses per kilometer is chosen and as the input is arranged to always be greater than 1200 pulses per kilometer the calibration divider will be set per installation to inhibit one pulse in every one of a predetermined number of pulses to give the standard rate of 1200 pulses per kilometer. To this end the calibration circuit is arranged so that one pulse in every X pulses (where X is presetable) is prevented from being applied to the clock generator. This calibration circuit utilises a divide by 64 counter which counts distance pulses from the monostable 7 these pulses are also applied to a J.K. flip flop 9. When the predetermined number of pulses has been accumulated the counter 8 disables the J.K. flip flop for one pulse and resets itself to its initial state. Thus, one pulse will be omitted in every X pulses, where X can be any number from two to 64 settable by way of calibration switches 10. The output from the calibration divider 8 at the rate of e.g. 1200 pulses per kilometer is then fed as a distance trigger pulse into a master oscillator circuit 11 as will be described further later. From the calibration divider the distance pulses are applied to the J.K. flip flop 9 and nand gate 12. The output of gate 12 is used as a trigger input to an oscillator in the form of an astable multivibrator 13, the operation of which will now be discussed. The astable multivibrator 5 has a free running frequency proportional to the waiting time, typically six pulses per second, each of these pulses ensuring that the J.K.F.F. 9 is in the reset state. In this state nand gate 12 will prevent the distance pulses from triggering the astable 13. If however the distance pulses are faster then six pulses per second, then more than one pulse will appear. between two astable pulses. The first will set the J.K.F.F. 9, preparing the gate 12 to pass the next pulse which will trigger the astable, terminating its relaxation period causing a pulse from the astable to conform with the distance pulse. Provided the distance pulse rate does not fall below the astables free running rate, the astables output will continue to conform to the distance pulses. Mode determination and annuciation is provided by monostable 40. The continuing presence of the trigger holds the monostable in the set state representing the distance mode, the absence of trigger pulses allows the monostable to reset, displaying the waiting time mode.