Messure the RPM through the bord-voltage

[Pedro Pinto]

Hello
I heard that is possible to determine the RPM rotations of a diesel motor through the Bord-voltage of the car through the messure of the ripple "spikes" of the voltage.
Does anyone know how or have idea and perhaps a schematic of a circuit to do this, with a pic controller?

Best regards
Pedro

[mister_e]

I wouldn't try it myself that way... I would probably hook-up a Hall-Effect sensor on the Alternator and read the signal from there.

[Acetronics2]

Hi, Steve

Not PBP ... but working !

http://www.vermontficks.org/pic.htm

look for "diesel Tachometer" ...

Alain

[mister_e]

Yup, and depending of the Alternator, some already have an output on... some ford and GM has it in the past when I installed Remote-Starter.... a bit why I also suggest the Hall-Effect sensor... I used a load of the following in the past
http://shopping.canoe.ca/shop/product--catId_1001602__locale_en__productId_1850446.html#S TIDetailedSpecs
I think they use Hall-Effect or a simple microphone...

Pedro, look at DEI, they do a module like you want... but still I wouldn't use it Myself.
http://carjamz.com/zen/index.php?main_page=product_info&cPath=450_459_461&products_id=3722

Sure enough it's easy to do, what i figure out is to use an Voltage comparator (and/or op-amp). You use a capacitor to remove the DC signal from the 12V line, then you should have only the remaining spikes, adjust your voltage reference to pick up the most interesting one, and play with it. A bit of experimenting should do the trick.... how accurate??? Can't tell... you know, there's some kind of people who have 1 Farad capacitor for their PowerAmp.. how does it affect the noise? I guess experimenting would reveal... on the other side... 1 Farad is no way a decoupling cap :D

And oh.. what happen to the noise when you play with your vehicle fan speed? How about when the Radiator fan start/stop?

Maybe why I wouldn't pick-up the noise from the DC line, but use Hall-Effect (or kind of) sensor instead, directly mounted on the alternator.