Software Dyno...

[Rich Vandervoort]

Here's how we used to get wheels speeds from competitors ABS systems.  Tap 
into the wheel speed signal at the ABS controller.  Note use twisted pair 
wiring with a grounded shield, do not route near spark plug wires or similar 
noise sources.  The consequence of noise on wheel speeds can be no brakes.   
Just use an off the shelf F to V converter (frequency to voltage) and feed 
the resulting analog signal into something that can use to record the signal 
versus time.  Calibrate a voltage to speed conversion using steady speed and 
some reliable speed measurement device(speedo?).  Note use an undriven wheel 
and the signal will be extremely accurate as there are usually something 
like 50 teeth on a speed ring.  Note your wheel speed tap may put noise on 
the speed signal if you do not match the polarity of the F to V and the ABS 
controller.  Also the newer ABS systems have quite sophisticated wheel speed 
diagnostic circuits and may disable ABS once the F to V is hooked up.  We 
used to buffer the signal, but I am unsure of the circuitry.


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