Abstract: A tachometer signal conditioning circuit (20) includes a timer circuit (48) responsive to ignition pulses from the primary lead (28) of an internal combustion engine ignition coil (26), and outputting a timing pulse terminating after a given time delay interval during which RFI, EMI and other transients on the primary lead (28) are ignored. A one shot monostable multivibrator circuit (56) responds to the trailing edge of the timing pulse and outputs a trigger pulse of given duration. A switch circuit (66) is connected to the battery circuit (22) and is turned on by the leading edge of the trigger pulse and turned off by the trailing edge of the trigger pulse, all before the next ignition pulse. The switch circuit (66) has a node (80) providing an input for a standard low voltage tachometer (82). Conductive and nonconductive states of the switch circuit (66) change the battery circuit voltage at the node (80) at a frequency corresponding to the frequency of the ignition pulses.

Abstract: A digital tachometer (2) is provided for two and four cycle internal combustion engines. A transformer (14) senses ignition pulses on the primary lead (6) of the ignition coil (4) of the two cycle engine, and an electrical connector (64) senses ignition pulses at the primary lead post terminal (66) of the ignition coil (54) of the four cycle engine. First and second signal conditioning circuits (50 and 96) are provided for each ignition pulse sensor for polarity immunity, RFI suppression, and transient and overvoltage protection. A precision timer (166) responds to pulses from the signal conditioning circuitry and outputs an output pulse of given delay, and ignores other pulses from the signal conditioning circuitry during the given delay, to protect against transient false triggering, especially in breaker point ignition systems. A phase-locked loop (186) responds to the delay pulses and outputs a pulse train having a frequency which is a function of frequency of the delay pulses.

Abstract: A temperature compensated flow sensor (10) for monitoring oil flow to a two-cycle engine includes a magnetic flow sensing body (26) mounted in a flow sensing bore (21). The position of the flow sensing body is detected by a Hall switch (42) to provide an electrical output indicating a flow or a no flow condition. The flow sensing body (26) is biased toward the Hall switch (42) by a spring (27) and a spring follower (31) controls the spring rate as a function of temperature. A thermal power element (35) moves the spring follower as a function of temperature to compensate for the change of oil viscosity with temperature.

Abstract: In an internal combustion engine an automatic fuel pump switch connects a fuel pump motor to the battery. An electronic sensing circuit is connected to the output winding of an engine-driven alternator which is also connected to charge the battery. The sensing circuit includes a sensing transistor connected to continuously sense the two instantaneous voltages relating to ground that appear as alternating current (A.C.) voltages at the opposite ends of the alternator output winding and produces an output only when one voltage is above a selected positive level while the other voltage is lower than the first voltage by a minimum amount. A control transistor circuit is connected to the output of the sensing transistor and is turned on to operate the fuel pump only when the engine is turning over at a sufficient rate to start and run.