Editing Hall effect sensor (section)

==== Ignition timing ====
Commonly used in distributors for ignition timing (and in some types of crank- and camshaft-position sensors for injection pulse timing, speed sensing, etc.) the Hall Effect sensor is used as a direct replacement for the [[Contact breaker|mechanical breaker points]] used in earlier automotive applications. Its use as an ignition timing device in various distributor types is as follows: a stationary permanent magnet and semiconductor Hall Effect chip are mounted next to each other separated by an air gap, forming the Hall Effect sensor.

A metal rotor consisting of windows or tabs is mounted to a shaft and arranged so that during shaft rotation, the windows or tabs pass through the air gap between the permanent magnet and semiconductor Hall chip. This effectively shields and exposes the Hall chip to the permanent magnet's field respective of whether a tab or window is passing through the Hall sensor. For ignition timing purposes, the metal rotor will have several equal-sized windows or tabs matching the number of engine cylinders (the #1 cylinder tab will always be unique for discernment by the Engine Control Unit).

This produces a uniform output similar to a [[Square wave (waveform)|square wave]] since the shielding and exposure time are equal. This signal is used by the engine computer or ECU to control ignition timing.