looking for an rpm switch

With all the knowledge on this board, maybe there's somebody who knows how to make an RPM switch ?
I'm looking for something that activate a relay at a preset RPM (say 5500 rpm).

I'd like the same thing, except have it be at a preset speed rather than a preset RPM.

Well both your requirements will be met by obtaining the output from a analogue sensor attached to whatever device it is you want to "control", this can usually be done by converting "pulses" from a sensor device attached to the crankshaft or rear wheels etc into either RPM or into "speed" - and form there into a settable control "signal"/pulse or whatever you required when the set RPM or speed is reached.

The conversion and control part will have to be done in a computer - either the Empeg itself, or in a small microprocessor.

The first (engine RPM) can be obtained from the RPM of the engine - this is probably available (digitally) from the OBD II inputs from your engine if the car is new, or from the engine by analogue/mechanical method.

Tony's request for "speed" can be obtained from the RPM of the wheels - either as read from the drive shaft between the gear box output and the (rear) wheels [assuming rear wheel drive car], or from the RPM of the wheels. [or with a OBD II input if you car has one].

I recall Jim Hogan made a post last year about a mechanical device he was going to fit to his car for rallying purposes to measure the wheel RPM (it used a small magnet and a Hall sensor from memory) - and from what I read it sounded pretty rugged (well it would have to be to last on a Rally car).
so, for speed that would be one way to go.

You could use the same idea for engine RPM by attaching the small magnet to an external part of the engine that rotates [e.g. the pulley wheel that drives the alternator by belt which usually comes off one end of the crankshaft (the other goes to the gear box) - or even the alternator pulley wheel itself as thats driven in a fixed relationship between engine RPM and alternator RPM - you would need a conversion factor to convert from alternator RPM to engine RPM, and assuming no belt slippage, it will work ok.

In Either case some conversion factor between "RPM" of the part being measured and the actual engine or vehicle RPM or speed would be needed - but that would be handled in the software as would the end result of some kind of "limiting" output.

I'm hoping to find something pre-made. I'd think one could get that data from the OBD-2 connector pretty easily...

Well depends what you want to do i could give you a design for an mechanical speed switch but it would be damn heavy.

but what are you trying to do as that kind of speed sounds like you might be looking at a change light as lots of those avaliable comercially.

Heavy? This going to be the design of speed switch for a ship?

- Trevor

Yes, but it's max reading would be, what, 500RPM?

Okay last diesel i sailed on max rpm was 72 rpm not 720 but a mere 72 You can count the pistons firing


but the t/a would spin up to about 10000 rpm or there abouts so we have an overspeed trip on those to stop them bursting if they go to fast. An hydraulic system that dumps oil pressure from the hydraulics that keep the steam valves open

I don't know if this is what you're looking for, it's a RPM Activated Switch made by MSD Igintion.

http://www.msdignition.com/1rpmacc.htm#anchor63270

The RPM is selected by using a RPM Pill. They also make RPM Window switches that active in a certain 'Window' aka RPM range.

We use them all the time on fast 'street' cars and race cars.

-Chuck

Yes, that's what I'm looking for. The only problem is that these things cost $60 + $25 for a rpm 'kit.
By the time these things get to Belgium, it's easily $130-150
Also, they have 100 rpm modules only. It would like to have a bit more precision (like switching at 5550 rpm instead of 5500 or 5600).

What I'm actually trying to do is having a solenoid close a valve in my intake manifold. The stock computer of the car (miata) has an output that powers the solenoid at 5250 rpm.
I have an aftermarket ecu without free outputs, hence the need for such a switch...

Frank

about a mechanical device he was going to fit to his car for rallying purposes

Well, I did install that (a 3-wire hall-effect sensor epoxied inside a threaded brass tube) and it works great, but it has no intelligence of its own -- you'd have to program something to interpret pulses. We epoxied 2 magnets to the axle shaft, so that if 1 broke off, we could still reprogram the rally computer to 1/2 the number of pulses.

So, I now understand why Frank wants the RPM sensor, but am trying to figure why Tony wants a fixed speed sensor. Mute audio output when speed > 140?

You could probably do a lot of these things with a kernel driver and lights-on detect/mute lines into the empeg; they can be programmed to generate interrupts on an edge and should easily be able to handle a lightweight IRQ several thousand times a second

Hugo

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but am trying to figure why Tony wants a fixed speed sensor. Mute audio output when speed > 140?

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From memory:
either:

Something to do with muting his Radar detector below a certain speed?

Something to do with speed controlled volume?

Tony did a post about his wish around this a while back...
[I'll leave it to Tony to provide the link :-)]

Something to do with muting his Radar detector below a certain speed?

Yup, that was it.

See, the only irritating thing about radar detectors is how frequently they give false alarms in grocery store parking lots. But if I muted the thing at speeds less than 30mph, then 90 percent of the false alarms would be eliminated.

Another fun thing would be to have it be selectable to either 30 or 65. When on the highway, I could flip it to 65 and then I wouldn't care about it beeping at me unless I was really speeding. But I'd be happy with just 30.

Regarding speed-sensitive volume control-- I still believe that an ambient noise sensor is a better way to handle that, because different road surfaces make different amounts of noise at a given speed. I could be going 100 on a nice road, and not need the music nearly as loud as going 50 on a rough road.

Seems, this could be what we're looking for.
Gonna try to mock up something with the LM2917 ...

Oops, forgot to add the link:
http://www.national.com/ds/LM/LM2907.pdf

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Another fun thing would be to have it be selectable to either 30 or 65. When on the highway, I could flip it to 65 and then I wouldn't care about it beeping at me unless I was really speeding. But I'd be happy with just 30

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Just talking outta my a$$ here... but I thought one of the coolest feature of GPSapp was that it shows your MPH... maybe something simple could be written to grab the mph info from the gps to throw a flag when you go below 30? I'm wondering if you could rig it on the telephone mute line (that I've never had a use for). I realize that this might not be possible (but it'd be cool)

I thought that telephone mute was an input to the empeg...

As I said... I'm talking outta my a$$ it probably (and most likely) is an input. I'm just curious as to if the there would be anyway to do whats being talked about with gps data. Hugo's earlier post got me thinking when he said You could probably do a lot of these things with a kernel driver and lights-on detect/mute lines into the empeg

but I thought one of the coolest feature of GPSapp was that it shows your MPH... maybe something simple could be written to grab the mph info from the gps to throw a flag when you go below 30?

Although something like this would be theoretically possible, I'd prefer to have this be separate from the empeg. There are times when I drive without the empeg, or when I've got it turned off, and I don't want to depend upon it in order to have my radar detector work properly.

Besides, there's still some bugs in GPSapp (or maybe they're hijack bugs) that cause the I/O to lock up after you've left it running a while. I'd rather have something more reliable than that controlling my radar detector.