How to get Tachometer with Alternator off?

[tinkrman69]

Originally Posted by mbartosch

I have been trying to get information about the nature of the Tachometer signal itself (in my case the one coming out of a Balmar MC 614) but was unable to find any details on this.

I would like to "extract" the tach signal for processing in DIY electronics (something like tachometer software on a micro controller). Can anybody tell me the nature of this signal?

I *assume* it's a 12 V square wave. From what I read I'd expect the frequency to either equal the actual RPMs (i. e. 1 kHz => 1000 RPM) or being a multiple of that (probably 6 or 12 times this value, e. g. 12 kHz => 1000 RPM).

I'd appreciate any information or pointers to documentation.

(Apologies for the slightly offtopic post for this thread, but didn't think starting a new one was necessary.)

It goes by pulses off one of the inlet side of the rectifier bridge. the amount of pulses is determined by the number of coils in the alt. How ever many coils will determine how many pulses per revolution.

It sounds like you are going to reinvent the wheel. everything you need to make a solid state circuit work is already in the system, unless you are wanting to redesign the tachometer. then go look at a digital tack there is the circuitry you'll be making.