Speedometer pulses per mile - SuperHawk Forum


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Old 04-23-2008, 03:38 PM   #1
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Speedometer pulses per mile

Hi All,

I'm installing an aftermarket speedo and need to find out how many pulses per mile the speedometer sensor in the transmission puts out.

Thanx
Chris
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Old 04-27-2008, 02:43 PM   #2
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The speedo sensor takes pulses from 5th gear driven sprocket. It has 27 teeth. You can easily calculate pulses for mile knowing final gear ratio and rear tire rolling diameter.

Do you know waht kind of sensor is this speedo sensor?
Is it an Hall effect sensor or what else?
Bye.

Last edited by Riccardo; 04-28-2008 at 02:34 PM. Reason: Bad english!
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Old 04-28-2008, 02:26 PM   #3
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I assumed it's a hall effect sensor. I'm getting pulses, but much past 10 mph and my speedo can't keep up with them. Help me out with the math

tire circumference = 79.5"
1 mile = 63360" = 797.16 tire revolutions per mile (trpm)

assuming 16/41 sprockets, 2.56 ratio

797.16 trpm = 2042.72 front sprocket revolutions per mile (fsrpm)


That's as far as I can get with my limited knowledge of transmissions and ratios.

Thanx
Chris
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Old 04-28-2008, 02:55 PM   #4
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Originally Posted by flyingeyepro View Post
I assumed it's a hall effect sensor.
Someone else can confirm that?

Quote:
I'm getting pulses, but much past 10 mph and my speedo can't keep up with them.
I can't understand what you mean!
You havent any pulse above 10 mph, or your speedo do not display any higher speed than 10 mph?
Waht kind of aftermarket speedo are you using? I'm messing with a Veypor VR2.

Quote:
Help me out with the math

tire circumference = 79.5"
1 mile = 63360" = 797.16 tire revolutions per mile (trpm)

assuming 16/41 sprockets, 2.56 ratio

797.16 trpm = 2042.72 front sprocket revolutions per mile (fsrpm)
I'm not so skilled with imperial units, but your calculations seems quite right.
The only correction I have to do is that 63360/79.5 gives 796.98 not 797.16 trpm. According to this, fsrpm are 2040.27. To obtain pulses for mile you need , you have to multiply it for 27, the number of teeth that generates pulses. The requested value should be 55087.29.
I guess that you can approximate it to 55000 without any influence in accuracy.

Bye.
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Old 04-28-2008, 04:11 PM   #5
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That explains it. My speedometer is a Nordskog M9222.

http://www.streetperformance.com/par...546-m9222.html

It's only good for up to 32000 pulses per mile. So when I was trying to calibrate it, I was able to monitor the input pulses, while accelerating from a stop. When I reached 15mph or so, the display started flashing, meaning that the pulses were out of range. I believe the problem is that pulse frequency is too fast for the speedometer. I suspected that was the problem. My next project is to build a pulse divider using a LM4017 decade counter. I can use that to divide the pulses by a factor of 10. So 55000 pulses per mile would translate to 5500 pulses per mile. I'll let you know how it works.

Thanx
Chris
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Old 04-28-2008, 04:59 PM   #6
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Can't you make, or doesn't it come with, a device that you attach to your fork which picks up a signal from a magnet attached to the front wheel? I know the bicycle computers use these commonly, as does the Acewell cluster I bought for another project.
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Old 04-29-2008, 03:57 PM   #7
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Quote:
Originally Posted by flyingeyepro View Post
I believe the problem is that pulse frequency is too fast for the speedometer. I suspected that was the problem.
I've the same suspect for my Veypor VR2.

Quote:
My next project is to build a pulse divider using a LM4017 decade counter. I can use that to divide the pulses by a factor of 10. So 55000 pulses per mile would translate to 5500 pulses per mile.
That's a good idea!
At the moment I'll solve my problem not using the stock VTR speed sensor but the one that comes with the Veypor.
But I'll not give up!

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I'll let you know how it works.
I rely on you!!!

Bye
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Old 04-29-2008, 05:46 PM   #8
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I did that when I had the speedometer mounted on a previous 88 CBR1000f Hurricane. It worked, but I would rather use the stock sensor. I can get the IC for about $2 and a blank circuit board for another $1. A decent pickup is $20+.

Thanx
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Old 05-16-2008, 04:01 PM   #9
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Didn't work. Too much RF from the spark plugs. I scoped it and it looked like white noise. Worked fine while the engine wasn't running. Not very useful though. I'm going with the reed switch and a magnet.

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Old 05-31-2008, 03:46 PM   #10
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Originally Posted by flyingeyepro View Post
Didn't work. Too much RF from the spark plugs. I scoped it and it looked like white noise. Worked fine while the engine wasn't running. Not very useful though. I'm going with the reed switch and a magnet.

Chris

That's not a good news!
Anyway, thank you. I'll not lose more time trying to use this signal.

Bye
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