Help! Need rpm activated switch w/ hysteresis!!

[John Andrianakis]

You can build one yourself! Take a look at National Semiconductors web 
page. The datasheet for LM 2907/2917 has a couple of rpm activated switches 
with hysterisis. LM2917 is a frequency to voltage converter particularly 
suited to tachometer applications.Check it out.
Regards,
John Andrianakis.

On Wednesday, March 10, 1999 8:38 AM, Jason [SMTP:srgnt03 at earthlink.net] 
wrote:
> I need some help here, and soon. I have a variable geometry manifold
> (Schrick VGi) that uses vacuum to open up an interior flap that changes
> the runner geometry and thus the torque curve. It uses a controller,
> two-way vacuum switch, and a vacuum tank.
>
> The controller has a ground, switched 12V+, an rpm signal tap from the
> factory Bosch ECU, and a two pin connector that it uses to activate the
> two-way vacuum switch (that's connected to a little diaphram that opens
> the flap in the manifold). The controller has an adjustable rpm set
> point for the rpm opening point (adjustable from 2K-6.3K rpm), and it
> has an adjustable hysteresis setting from 0-200 rpm. The best torque is
> made when the settings are 4K for the flap to open (short runners, high
> hp up top), and a 50 rpm hysteresis (so it closes at 3950 rpm). Works
> VERY well when all is functional. Rpm set points are made by DIP
> switches (8 of them). Test mode will cycle the switch on/off (set all
> DIP switches ot OFF), and turn the LED from green(closed flap) to red
> (open flap, and back...
>
> The controller is done for. It will not even function in test mode. A
> new one is $300. That's insane, for such a simple PCB. I tested ALL my
> connections for continuity, and all check out. The wiring is sound, and
> everything checks out. The controller will activate the two-way vacuum
> switch as soon as it gets switched power. Regardless of rpm signal, or
> set point. I looked at the PCB (encased in epoxy, except for the DIP
> switches)and there appears to be a little discoloration or corrosion in
> there. I'm an ME, not an EE...so I need a replacement controller.
>
> I looked at my Summit Racing catalog (pg. 119 & 126)and found a couple
> rpm switches...but I don't think any of them have a hysteresis function.
> The MSD one has a "low" and a "high", but that's it. I need something
> that offers me adjustability from 3500-4500 rpm, with about a 50-100 rpm
> hysteresis. I don't want to fab a PCB, I don't want to spend over $100,
> and I need something soon. Without a controller, I have to choose
> between low end torque, or high end power (by having the flap closed, or
> open all the time). Drive-ability is less than perfect.
>
> So, does anybody know of an rpm switch that has an adjustable "on", but
> also has a hysteresis setting too? Maybe I could get the MSD unit, and
> set the "off" rpm set point lower than the "on" set point (an have a
> negative overlap, making my own hysteresis)???? Thoughts?
>
> Jason
> '93 VW Corrado VR6 w/ failing Schrick VGi controller!!