Browse Prior Art Database

SELF-POWERED TACHOMETER CIRCUIT

IP.com Disclosure Number: IPCOM000005500D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 60K

Publishing Venue

Motorola

Related People

Robert W. Deutsch: AUTHOR

Abstract

A tachometer circuit which derives its power from the signal it is monitoring is shown below. It is particularly suited for measuring engine velocity and acceleration, but may be used to monitor and filter noisy, repetitious waveforms so that the signal switching frequency may be determined accurate- ly. In normal use it may be connected to the primary side of an automobile ignition coil which is being controlled electronically or mechanically.

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rM'; MOTOROLA Technlcal Developments Volume 3 March 1983

SELF-POWERED TACHOMETER CIRCUIT

By Robert W. Deutsch

   A tachometer circuit which derives its power from the signal it is monitoring is shown below. It is particularly suited for measuring engine velocity and acceleration, but may be used to monitor and filter noisy, repetitious waveforms so that the signal switching frequency may be determined accurate- ly. In normal use it may be connected to the primary side of an automobile ignition coil which is being controlled electronically or mechanically.

   Since the power necessary to operate the circuit is obtained from the input, only two connections are necessary (signal and ground). The output is a fixed pulse width triggered by the first excursion of the input voltage above VTH + after being below VTH -.

   The circuit supply is clamped to ten volts by Rf and 21. Enough energy is stored in the capacitor CT to power the circuit for more than five seconds. Cl will charge up to a satisfactory operating voltage (from 0.0 volts) in one second through D1 and Rf. QT, Q2, R2, R , R and C2 form a higli voltage Schmitt triggerwith VTRf = 7V, VTR ?

Rd, RS, RS,

                       r = 2.5V with the va ues shown. C2 alters out most of the high frequency components of the input. I 2 1 and its timing components (R8 and C3) form a non- retriggerable one-shot which generates a fixed width pulse when triggered.

0 Motorola, Inc. 1983 55

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