Self-powered tachometer circuit

Claim 2

A self-powered tachometer circuit for indicating engine RPM including in combination, variable reluctance pickup means having first and second terminals, with said first terminal being connected to a reference potential, moving means operated by the engine for inducing in said pickup means an alternating current having a frequency proportional to the speed of engine revolutions, meter means for indicating the engine RPM having first and second terminals, with said second terminal connected to the reference potential, a voltage doubler circuit connected to said second terminal of said variable reluctance pickup means and to the reference potential and having an output terminal for providing a voltage with respect to the reference potential for energizing the circuit, pulsing circuit means connected in circuit with said variable reluctance pickup means, said pulsing circuit means including a first capacitor having first and second electrodes, with said first electrode connected to said output terminal of said voltage doubler and said second electrode coupled to said first terminal of said meter means, an electron switch connected between said first electrode of said first capacitor and the reference potential and having a control terminal, and a second capacitor connected between said second terminal of said variable reluctance pickup means and said control terminal of said electron switch, said first capacitor being charged by said voltage doubler circuit to apply potential to said meter means, said second capacitor being responsive to a signal of a predetermined polarity from said variable reluctance pickup means to apply a potential to said control terminal of said electron switch to actuate the same and discharge said first capacitor.

Claim 3

A self-powered tachometer circuit according to claim 1 wherein said electron switch is a transistor having collector, emitter and base electrodes, with said collector electrode connected to said first electrode of said capacitor, said emitter electrode connected to the reference potential, and said base electrode forming said control terminal.

Claim 4

A self-powered tachometer circuit in accordance with claim 1 further including a resistor connected between said control terminal and the reference potential, said resistor having a value to permit charging of said second capacitor in a short time to de-actuate said electron switch and allow said first capacitor to charge from said voltage doubler circuit.

Claim 5

A self-powered tachometer circuit in accordance with claim 1 including voltage reference means connected across said voltage doubler circuit for providing a substantially constant voltage thereacross.

Claim 6

In a self-powered tachometer circuit, the combination including, variable reluctance pickup means having first and second terminals with said first terminal connected to a reference potential, a rotating structure having ring gear means for cyclically inducing an alternating current in said pickup means having a frequency proportional to the revolution rate of said rotating sTructure, a voltage doubler circuit connected to said second terminal of said variable reluctance pickup means and to the reference potential and having an output terminal for providing a voltage with respect to the reference potential, a meter having first and second terminals with said second terminal connected to the reference potential, means including a first capacitor having a first electrode connected to said output terminal of said voltage doubler circuit and a second electrode coupled to said first terminal of said meter, discharge circuit means connected to said first capacitor including a transistor having a control electrode, and output electrodes connected between said first electrode of said first capacitor and the reference potential, a second capacitor connected between said second terminal of said variable reluctance pickup means and said control electrode, said first capacitor being charged from said voltage doubler circuit in response to a signal from said pickup means of one polarity followed by a signal of the opposite polarity to operate said meter, resistor means connected between said control electrode and the reference potential and in series with said second capacitor to form a time base circuit therewith having a relatively short time constant, said second capacitor being responsive to a signal from said pickup means of said opposite polarity to energize said transistor thereby discharging said first capacitor, said second capacitor charging in a relatively short time to turn off said transistor thereby stopping the discharge of said first capacitor to permit the same to be charged by said voltage doubler circuit.

Claim 7

In a self-powered tachometer circuit, the combination including, variable reluctance pickup means having first and second terminals with said first terminal connected to a reference potential, a rotating structure having ring gear means for cyclically inducing an alternating current in said pickup means having a frequency proportional to the revolution rate of said rotating sTructure, a voltage doubler circuit connected to said second terminal of said variable reluctance pickup means and to the reference potential and having an output terminal for providing a voltage with respect to the reference potential, a meter having first and second terminals with said second terminal connected to the reference potential, means including a first capacitor having a first electrode connected to said output terminal of said voltage doubler circuit and a second electrode coupled to said first terminal of said meter, discharge circuit means connected to said first capacitor including a transistor having a control electrode, and output electrodes connected between said first electrode of said first capacitor and the reference potential, a second capacitor connected between said second terminal of said variable reluctance pickup means and said control electrode, said first capacitor being charged from said voltage doubler circuit in response to a signal from said pickup means of one polarity followed by a signal of the opposite polarity to operate said meter, resistor means connected between said control electrode and the reference potential and in series with said second capacitor to form a time base circuit therewith having a relatively short time constant, said second capacitor being responsive to a signal from said pickup means of said opposite polarity to energize said transistor thereby discharging said first capacitor, said second capacitor charging in a relatively short time to turn off said transistor thereby stopping the discharge of said first capacitor to permit the same to be charged by said voltage doubler circuit.