how to measure speed of toothed wheel with vr sensor

diesel62

Hello
Can someone please point me in the right direction ,I would like to know how to interface a vr sensor to the propellor to measure shaft speed from a toothed wheel.
I have looked through the forums but cant find anything.could someone please help.
thanks·

Phil Pilgrim (PhiPi)

If you're using an unconditioned VR output (i.e. sinewave), I'd start with something like this to interface to the Prop. You may need to adjust some values for the most reliable operation.



The first cap and diodes will clip the incoming waveform to 1.2V P-P. That is further coupled to a divider network set to just above the Prop's input threshold. This feeds the input to a counter operating in mode $01011, which is a positive edge counter with negative feedback. The feedback pin drives an NPN inverter, which alters the input bias in such a way as to provide about a 3.4% hysteresis.

-Phil

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Post Edited (Phil Pilgrim (PhiPi)) : 11/1/2009 12:48:26 AM GMT

diesel62

Thanks for that much appreciated.

kwinn

You may as well leave out the 100K resistor in this circuit since it is in parallel with the 2.2K. The resulting resistance is 2.15K, which is well within the range of a 5% resistor.

pmrobert

Another option is www.national.com/mpf/LM/LM1815.html. Nice chip, $1.50US, works well. It does require a couple of discrete components.

-Mike

Velocit

Yet another option is the VR conditioning circuit from the MegaSquirt project:

www.megamanual.com/ms2/v3pcb_3.gif

You shouldn't need the U7B portion of the circuit, unless you want an inverted signal.

The LM1815 is also a good option, though. Many MegaSquirt users use that chip to add a second VR input to their ECU's.

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-Paul

Phil Pilgrim (PhiPi)

After seeing the LM1815's specs, it's probably safe to say that my circuit is way underspecified. I'd go with the National part.

-Phil