What voltage / amperage / frequencies can I expect from the tach line of a 2001 eclipse v6?

The question is all in the title, but any way.  What numbers can I expect to see from the tachometer signal line of my 2001 mitsubishi eclipse v6?  I've read that some times it can be like 3 cycles for every 1 RPM.  I would assume it was running at 12 volts, but is this false?  What kind of amperage could I expect to be pulled on that line as well?  I plan on connecting an arduino to this to get the frequency as an input (new new new newbie to arduinos!).  Can I expect to need to step down the voltage, if so, how?  Is there some basic principle or standard for the tach line that I am unaware of?  Any help with the tach line info or how I should connect it to the atmega chip would be AWESOMELY helpful!!!
-James

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sephiroth67 (author) 7 years ago
Confirmed to run at 12-14 volts. My cheap radioshack multimeter blew its fuse once I checked amperage. The Frequency was a bit crazy, but it did rise as I pushed the throttle. It would need to be calmed down for this application I guess (hysteresis?). Looked like it was just floating in a 300hz range that would go up as I open the throttle and down as I let off.
You don't measure current the same way as voltage - you'll just short it out.
Of course the fuse blows.
NachoMahma7 years ago
.  If you are getting 3 pulses per revolution and you have a six cylinder engine, then it sounds a lot like the "old school" tachs that used the spikes from the ignition coil. I doubt that same method is used today (the spikes can be quite large), so I'd investigate the TDC (AKA crankshaft position) sensor that steveastrouk mentioned.
.  To get the right answer, your best bet may be to call a Mitsubishi dealer/service center. Or maybe Googling "2001 Mitsubishi Eclipse tachometer specs"
sephiroth67 (author)  NachoMahma7 years ago
Turns out it was sitting in front of me the whole time, I just needed to set my multimeter to AC...should've thought about that >.<

Anyway, now all I need to know is, how to get an AC line that can range from 5.5V - I'm gonna say maybe up to 70 volts even, into an arduino!?!?
. BTW... your meter is probably assuming a sine wave when measuring RMS AC and I think your signal is a pulse. You may not be getting accurate readings.
.  My first thought is to use a voltage divider, but you may find a better solution in the "Related" box to the right.
frollard7 years ago
What lots of people do is run signals like that through a Zener diode to block it down to a safe voltage, then run THAT through an opto-isolator to ensure there is no direct connection from a potentially high voltage source and your tasty Arduino.
As for the specifics of what frequency to expect, you'd need to look in your car's repair manual.
Or is it picked off the TDC sensor, which is usually inductive ?
Right, if it's an inductive signal, at high rpms you might see pretty high voltages...
Depends where you're picking it up - the ones I've got condition it in the sensor.

Or its a Hall effect sensor ?

Steve