# Tachometer Signal Spoofing?



## Tesseract (Sep 27, 2008)

Don't you have a Soliton? If so, you can set one of the outputs to create a signal that will drive most (not all!) analog tachometers. You can even set the output to a different pulse per turn than the input.

And 4cyl. usually require 2 ppt for the tach signal.

As for measuring your motor's speed, get the controller working with a tach sensor and you'll know it soon enough and can then compare what logger says to the dash tach to make sure they are in agreement.


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## TigerNut (Dec 18, 2009)

PeterH said:


> Hi there,
> 
> I have two questions related to running my factory installed tachometer in my Geo Tracker.
> 
> ...


If you had a four cylinder engine then you would have had two ignition pulses per revolution. Most likely, your tach will also be calibrated for two pulses per revolution. You should review the wiring diagram for the ICE installation; if you had a tach sense wire running from the ignition coil (-) terminal to the tach, then try driving that line with a 12V square wave of about 50% duty cycle. If the tach signal was provided by the engine management system, then still, you could try a 12V square wave, or be safe and start with 5V and go up until you get a reading... it might be prudent to put 100 ohms (or so) in series with your test signal output and the tach input on the instrument cluster, just to prevent any Real Bad Stuff from occurring.

Tachs that are designed to run off the coil negative connection, have to be tolerant of input voltages of over 100V because of the flyback pulse when the coil current is cut off and it triggers a spark across the plug. So driving 12V to the tach input of older tachs is unlikely to cause any damage; in fact you may find that the tach will not respond unless you create a substantially higher voltage.

I don't think that any current manufacturer uses the Smiths style of inductively coupled current sensing... that went out in the 60's.


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## PeterH (Mar 20, 2009)

That is all good info.... thanks guys.

Main reason for wanting to spoof the tach is because I'm having trouble identifying the line from the engine to the tach so i was hoping to come up with a way to test what I think is the right wire before I put the dash back together.

At least I now have a good way to ensure the tach is reading correctly once the controller is powered and the motor is running!

Thanks,
Pete


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## Yukon_Shane (Jul 15, 2010)

PeterH said:


> That is all good info.... thanks guys.
> 
> Main reason for wanting to spoof the tach is because I'm having trouble identifying the line from the engine to the tach so i was hoping to come up with a way to test what I think is the right wire before I put the dash back together.
> 
> ...


Hey Pete,

In the tracker it'll be the brown wire on the right side of the instrument cluster that runs the tach.

With the soliton it's as easy as connecting that brown line to one of the solitons outputs and using the web interface to set it to 2 ppt and you're golden.

Easiest part of my build so far


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## PeterH (Mar 20, 2009)

Thanks Shane!

That is the wire I thought it was... just didn't have any way to confirm it.


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