pulse frequency limiter. (newb)

[denaldo]

Hi, I would like to start by saying my knowledge of electronics is limited.

I have a jetski that has a speed limiter. The limiter works off a paddle wheel speed sensor. The water travelling past the paddle wheel sends two 4.9V pulses per revolution to the speedo and engine control unit(ECU). When the ski reaches a certain speed, the electronic throttle valve pulls back limiting rpm and speed.

I tried disconnecting the speed sensor and unfortunately, the ECU sees this as a fault and scary red light comes on on the dash.

Ideally, I would like to put a module between speed sensor and ECU that limits the pulse frequency so the ECU dosen't know how fast the ski is going. As long as the ECU sees a pulse, it won't go into fault mode.

How do I go about this?

Thanks in advance from electronic toddler.

 

[hexreader]

I assume the speed limiter is there for safety reasons.

Are you asking forum members to help you to kill yourself?
Or worse still, someone else in the water with you.

 

[crutschow]

The Darwin Award is looking for applicants. Are you interested?

 

[denaldo]

Just for your info, the ski is limited to 67mph. This is to comply with USA coast guard exemptions.

The Euro units are not limited and do 69mph, 2 mph is hardly creating a death machine as the hull is good hor 90+mph with modified engine.

Also, im on the Gold Coast, Eastern Australia and are out of US coast guard juristriction.

I guess I should have explained this before...

 

[MikeMl]

So, would it work to just divide the pulse rate by two (halve the pulse rate)? You could just double the speedo indication. Is the pulse rate used for anything else that engine rpm would normally be used for (like spark advance)?

 

[denaldo]

So, would it work to just divide the pulse rate by two (halve the pulse rate)? You could just double the speedo indication. Is the pulse rate used for anything else that engine rpm would normally be used for (like spark advance)?

Funny you asked that. I thought of an issue 5 mins ago. The speed sensor has no effect on engine tune, ie. spark and fuel tables. However, the cruise control and no wake zone functions will be affected. Halving the pulse rate would be fine for racers as no wake and CC dosen't excite them much, but for a recreational rider this may be an issue. I guess I have to back probe the connector and measure the pulse rate whilst spinning the paddle wheel with compressed air. (much safer than riding ski)

Is it possible to make a module the basically puts a limit on pulse rate? That would retain full functionality below say, 64mph. And above that, who cares about CC?

Thanks for the reply, MikeMl.

 

[MikeMl]

Yes, but you would have to know the actual pulse rate vs actual speed in water. The paddle wheel has some "slippage", so you cannot assume what that is. Spinning it up with an air hose is likely to get much higher rates than in water. (think about spinning a bearing with an air hose).

How about dividing by two only for pulse rates greater than "X", where you have to determine what X is? Ideally, X would correspond to about 50mph.

 

[denaldo]

I agree mate, I know there is some slip, you know there is some slip, but the ecu dosen't.

I can hold dmm next to dash and get missus to blow speedo wheel until dash reads around 65mph and read dmm. (that should be good for an argument!)

If anyone is interested, the craft is a kawasaki 300X

thanks again.

 

[dougy83]

Is it possible to make a module the basically puts a limit on pulse rate? That would retain full functionality below say, 64mph. And above that, who cares about CC?

Yes, very possible & not difficult. If you can find out the pulse width and rate for the top speed I can duplicate it in a microcontroller - any pulse arriving slower than the max speed will be passed through; otherwise the microcontroller will create its own pulse train at whatever frequency you deem is the max allowable rate.

As an aside, you said 4.9V pulses - what voltage is the battery? It could well be the case, but if you're measuring the pulses with a DMM, it may be that the pulses are too narrow to measure the voltage correctly.

 

[denaldo]

The battery is 12V, but most, if not all the sensors operate off lower voltage. the service manual says 4.5-4.9V pulse and 0.05-0.09V off.

 

[MikeMl]

...
I can hold dmm next to dash and get missus to blow speedo wheel until dash reads around 65mph and read dmm. (that should be good for an argument!)...

Does your DMM have a freq counter in it?

 

[denaldo]

Yes it does, will measure tomorrow

 

[dougy83]

Could you measure the DC voltage also for a couple of frequencies too, so that we can guess at the pulse width (unless that's in the manual too)?