Circuit for producing pulses indicative of speed from a rotary generator

Abstract

The Schmitt trigger threshold switch which produces rectangular waves in response to the output of a rotary ignition timing generator has a variable bias applied to its switch-in threshold which is proportional to the amplitude of the generator output, while the switch-out threshold remains fixed at or near zero voltage. The bias, which may be developed by a peak detector, prevents inherent ignition timing shift as the generator turns faster. The Schmitt trigger utilizes an inverting comparator so that a 'lowest-wins' circuit can be used for applying stabilizing negative feedback or bias to the comparator. The bias provides immunity to disturbing voltages which increase with signal amplitude.