Digital speedometer

Claim 1

A digital speedometer for use in an automotive vehicle having an electrical power system and a rotatable mechanical speedometer driver comprising: a transducer arranged for mounting on said vehicle and adapted for engagement with said speedometer driver that is located within a vehicle transmission line housing in an automotive vehicle, wherein said transducer includes: a transducer housing with an annular threaded fitting adapted to threadably engage with a threaded speedometer driver access port in an said automotive vehicle transmission line housing, a shaft mounted for rotation within said transducer housing and having a termination at one end adapted for mechanical coupling with said speedometer driver and arranged coaxially within said threaded fitting, a rotatable member carried upon said shaft, an optical encoder operatively associated with said rotatable member for sensing speed of rotation thereof and for emitting pulses at a pulse rate responsive thereto, an electrical signal lead extending from said transducer housing, an electrical power lead extending from said transducer housing and connected to said vehicle power system, counting means coupled to receive pulses from said optical encoder on said electrical signal lead, and having a reset, buffer storage means connected to said counting means and having latch enabling means which, when enabled, load an accumulated pulse count from said counting means into said buffer storage means, display means remotely located from said transducer and connected to said buffer storage means for displaying an image representation of the number of pulses loaded in said buffer storage means, a variable oscillator for emitting periodic electrical pulses at a predetermined frequency less than the frequency of pulse emission from said optical encoder and having a common output connected both to said reset of said counting means and to said latch enabling means of said buffer storage means, to both enable said buffer storage means and thereafter to reset said counting means with the same pulse, oscillator adjustment means for varying the frequency of oscillator output, and electrical connections for obtaining electrical energy for said counting means, said display means, said buffer storage means, and for said oscillator and adapted for connection to the electrical power system of said automotive vehicle.