Re: [Q] Shaft speed measurement (again, based on response)

[Doug Pratt <doug@REALGOODS.COM>]

On Tue, 30 Dec 1997, Paul T. Mobbs wrote:

> <snip> could someone please tell me how this is done in cars. If I
> could find out how to make a standard RPM gauge work then I might have
> some hope for this.
>
> Don't the RPMs feed into the electronic control of an ICE for cruise
> control and other electronically controlled functions? If so, how is this
> interface done?

Modern RPM gauges are triggered by the pulse signal from the low voltage
side of the coil. Either breaker points, or electronic ignition will
provide the pulse. The older British designs and some motorcycles use a
mechanical cable drive, like a speedometer. If the cruise control is
factory installed, they'll probably pick up the RPM signal from the coil,
but some factory rigs, and all aftermarket units use an optical or
electromagnetic pickup on the driveshaft or axle.

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Re: [Q] Shaft speed measurement (again, based on response)                   R