[Diy_efi] Looking for some help on a speed sensor project

[Perry Harrington]

Ahh, you got one of them Toyota sensors now don't ya? :)

Go to www.national.com and get the datasheets on the LM2907 and LM339.

The 2907 is a freq to voltage convertor and the 339 is a quad comparator.

Setup the 2907 for your frequency range and use a couple of the 339's
comparators to make a window comparator.  Add a drive transistor and you
got a speed switch.

I believe both circuit applications are even in the app notes section.

Since you know that it puts out 8000ppm, you simply need to determine the
hz for speed:

Say target speed is 48mph
8000 * 48 = 384000 pphour
384000 / 60 = 6400 ppminute
6400 / 60 = 106.67 ppsecond

Or simplified:

Hz	= PPM * (Speed / 3600)
106.67 	= 8000 * (48 / 3600)

Speed 	= (Hz * 3600) / PPM

So at 48mph the sensor outputs a 106 & 2/3rd Hz squarwave.

--Perry

On Wed, Jun 19, 2002 at 09:08:44AM -0400, Saxon, Howard (AFS-Warren) wrote:
> Hello all.  I'm not too good at this but I'll try to describe what I want
> and what a "semi-knowledgeable" friend told me I need.  What I'm trying to
> do is trip 1 or 2 relays based on car speed, not RPM.  The car's speed
> sensor operates like this.  There are 2 contacts.  One is grounded and the
> other has 5 volts going to it.  Contacts inside close 8 times per revolution
> and the sensor internally rotates 1000 times per mile, so it puts out
> approximately 8000 pulses per mile.  What I need is to somehow turn on a
> relay at a certain "pulse per time" or speed and have it turn off if the
> speed drops below that point again - and have it adjustable so I can fine
> tune the car.  My friend said that, for starters, I need a "frequency
> counter" and then a way to convert that to a switchable signal.  Any help
> would be greatly appreciated.
> Thanx a lot,
> 
> Howard Saxon	
> Senior Designer
> Advanced Products
> Borg Warner AFS
> 810-497-4026
> hsaxon at afs.bwauto.com <mailto:hsaxon at afs.bwauto.com> 
> 
> 
> 
> 
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-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/		 

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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