How does the speedometer communicate with ECU? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 8 Old 07-13-2011, 09:02 AM Thread Starter
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How does the speedometer communicate with ECU?

I'm interested to understand how the speedometer works with the ECU.
Does it send a signal with varying voltage? i.e. Analog signal?
Or is it a digital signal?

The speedohealer does its magic somehow, it would be nice to know how that magic trick works.
[Not to worry: I have Zero commercial ambitions, just like to know 'How Things Work?', love that TV show]

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post #2 of 8 Old 07-13-2011, 04:48 PM Thread Starter
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Anybody?

The best I found so far is that a generic speedsensor sends pulses, one pulse for every time the magnet in the sensor makes a whole circle and meets the other magnet on the wheel.
So in that case a healer would probably detect the pulses, and need to regenerate slower pulses (typically by 5-10%, depending on the predefined error margin and/or mapping if such exists) to the ECU/speedometer.
There is some lag introduced in this solution, since at least a few pulses (I guess at least 3) need to be detected to get the current speed by analyzing their frequency - i.e. time gaps between each peak/pulse. So in low speed there would be more lag, but in high speed it would be much smaller (denser pulses).
A micro controller can easily perform such a task in real-time.

I just don't know if a v-strom speed sensor uses pulses..

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post #3 of 8 Old 07-13-2011, 04:58 PM
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The speedo sensor is a Hall effect device. It sends pulses.

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post #4 of 8 Old 07-13-2011, 05:40 PM Thread Starter
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Quote:
Originally Posted by greywolf View Post
The speedo sensor is a Hall effect device. It sends pulses.
Thank you for clarifying this.

In ABS models (like ours) there is a ring with small notches in each wheel, which doesn't exist in the non-ABS V-Stroms.
It is logical to assume that these are part of the ABS detection mechanism.

Does the ABS system detect a wheel lock by getting a zero speed reading that is very quick drop from a 'movement' speed reading (e.g. above 3MPH)?
Are these notches there to simply provide the hall effect device a better resolution? So instead of getting a pulse once per cycle (non ABS speed reading), it would read 50X (not sure it is the right number..doesn't matter) times more and provide 50X pulses per second?
Or is there a parallel mechanism for speed and for wheel lock detection?

If I'm correct and the speed mechanism for ABS is used for speed and wheel lock, an alarming thought came to my mind:
Assume one rides in 65MPH and has a speedhealer and suddenly the speedhealer dies (for what ever reason) - as a result it supplies an output of no pulses - Wouldn't this could cause the ECU to think that there is a wheel lock up? Or does ABS get invoked only if there is already some breaking detected?

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Last edited by BigMan73; 07-13-2011 at 05:41 PM. Reason: typos..
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post #5 of 8 Old 07-13-2011, 05:43 PM
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Is the speedhealer at the wheel/sensor end of the system, or after all that and intercepting the signal right before it gets to the actual speedo? I would think the thing does not change the sensor input to the ECU, but rather changes the ECO output going to the speedo.....? Just thinking out loud, I do not know how it is all configed.

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post #6 of 8 Old 07-13-2011, 05:55 PM
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The speedo sensor is in the left front and the ABS sensors are on the right. They function independently. I believe the ABS starts cycling on a locked wheel when the bike speed is over 3mph but I have zero information to verify that so it's really a guess. The speedo sensor has four pieces of steel passing the magnet but the ABS has very many.

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Last edited by greywolf; 07-13-2011 at 05:57 PM.
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post #7 of 8 Old 07-13-2011, 05:57 PM Thread Starter
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Quote:
Originally Posted by larry0071 View Post
Is the speedhealer at the wheel/sensor end of the system, or after all that and intercepting the signal right before it gets to the actual speedo? I would think the thing does not change the sensor input to the ECU, but rather changes the ECO output going to the speedo.....? Just thinking out loud, I do not know how it is all configed.
I do not know for sure, but here is the installation instructions:
SpeedoHealer.com

It seems that the speedohealer comes between the sensor/wheel and the ECU. If I'm wrong, my apologies in advance.

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post #8 of 8 Old 07-13-2011, 06:08 PM Thread Starter
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Quote:
Originally Posted by greywolf View Post
The speedo sensor is in the left front and the ABS sensors are on the right. They function independently. I believe the ABS starts cycling on a locked wheel when the bike speed is over 3mph but I have zero information to verify that so it's really a guess. The speedo sensor has four pieces of steel passing the magnet but the ABS has very many.
Thanks - I will look at the bike again following your description, which BTW makes a lot of sense, as it introduces a needed redundancy which adds safety.
I was toying in my head of building a speed healer ($115 for a small microcontroller, some cables and 3 connectos?!? it costs maybe $15 to manufacture and there is not much software code involved there - IMO ripoff), but the thought of having a software/hardware bug crash me on the highway due to a fake ABS lock is scary. If indeed the sensors are separate, I have no concerns over coding bugs..

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Last edited by BigMan73; 07-13-2011 at 07:08 PM.
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