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

[Saxon, Howard (AFS-Warren)]

First off, I'd like to say thank you to Jim, Eric, Perry, Scott, Brian and
someone with the e-mail name "md4etal" for replying to the question.  I
should have thought about my original post a little more, but I was directed
to this forum and basically just copied my original post onto this forum.  I
am very much a beginner in the electronics field and I bought a "beginners
guide to electronics", from Radio Shack, just last weekend.  So what I'm
getting at is that, while I am willing to learn, a lot of what you guys are
talking about is Greek to me.  I did download and read the datasheet on the
LM2907 and it does sound like the part I need to do what I want to do, but I
haven't a clue of what some of the symbols mean or how to choose the
supporting components.  They even reference locking the doors of a car a
certain speed  - or turning on a switch at a speed.

Jim, you said that if I can build it, you'd help design it, I'd like to take
you up on that offer.  Even if it didn't work the first time, I'd get the
experience soldering and trying to figure out what you are doing and why.

3 things that I forgot to mention - 
1.	The speed sensor still has to be connected to the car's computer so
I'd have to somehow eavesdrop on the pulsed output signal without affecting
the signal going to the computer. 
2.	I was going to actually have 2 relays get tripped at 2 different
speeds.  At one speed, say 25 MPH (55.56 pulses per second) a relay would
turn on, then at a higher speed, say 60 MPH (133 p/s) the second relay would
turn on.  Then as speed slows down, the relays turn off as the speed goes
below the value.
3.	If I could somehow have the speed targets be variable, like a rotary
knob, to fine tune the combination.

I really appreciate the help you guys have given me so far, it seems I'm in
the right direction now.

Thanx,
Howard 


	-----Original Message-----
	From:	Brian Dessent [SMTP:brian at dessent.net]
	Sent:	Thursday, June 20, 2002 7:51 PM
	To:	diy_efi at diy-efi.org
	Subject:	Re: [Diy_efi] Looking for some help on a speed
sensor project

	Perry Harrington wrote:

	> 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.

	No need for the external parts.  The 2907 has a built in
	opamp/comparator and NPN switching transistor (up to 50mA load) for
this
	very purpose.  p7 of the datasheet.

	Brian

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