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Old 05-11-2007, 04:39 PM   #1
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Alright guys lets put our thinking caps on. I bought a new bike, but because of the new sprocket and tires I have put on the bike my speedo is off by 7.76%.

I want to be able to put something inline to correct this error. The speed sensor on the tranny output, sends a frequency to the speedo cluster and that displays the MPH. Based on two data points given in the service manual, 181 Hz = 60mph and 88Hz = 60kph, there is approximately ~ 2.35 Hz/mph.

How do I intercept the frequency and and change it?
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Old 05-11-2007, 04:46 PM   #2
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Did you get the 7.76% from comparing indicated speed to a GPS?

I wonder what the accepted error of the unmolested setup is? On my completely stock Tribute the speedo is out by nearly 5km/h @ 110km/h. What's that nearly 5%? I've heard +-5% is typical. My Miata is even worse.

Who knows, maybe the changes you are making will improve the accuracy Check with a GPS or a stop watch and mile markers.

As to your actual question, I don't have a clue since I'm just a uselss ******* Canadian.
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Old 05-11-2007, 04:46 PM   #3
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Go back to the old sprocket
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Old 05-11-2007, 04:58 PM   #4
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Did you get the 7.76% from comparing indicated speed to a GPS?
No i got it from calculating the new gear ratios, I will measure the real error when I get home and can steal romanKs gps system for a run.
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Old 05-11-2007, 04:59 PM   #5
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Go back to the old sprocket
Thats more work than figuring this out.

Put those electrical skills to work.
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Old 05-11-2007, 05:27 PM   #6
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You still have access to whatever equipment your engineering dept. has, right? Or are you gone for good now? If you had access to a decent scope, I'd hook it up to the signal line and look at the shape of the wave. That'll shed some light onto what you'd have to do to change the frequency. In general though, wave signals aren't the easiest to change, unless it's like a pulse-counting system, which might be easier.
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Old 05-11-2007, 05:29 PM   #7
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**** the speedo. Unplug the speed sensor or remove the speedo sprocket. You can figure out speed by RPM. That's what I did with my GSXR.
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Old 05-11-2007, 05:35 PM   #8
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**** the speedo. Unplug the speed sensor or remove the speedo sprocket. You can figure out speed by RPM. That's what I did with my GSXR.
**** that, I like knowing how fast I go$$$$ PLust the speedo and RPM are all on the same board it will display an error where the MPH is usually.... annoying!
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Old 05-11-2007, 05:43 PM   #9
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Originally Posted by Atlanta93LE View Post
You still have access to whatever equipment your engineering dept. has, right? Or are you gone for good now? If you had access to a decent scope, I'd hook it up to the signal line and look at the shape of the wave. That'll shed some light onto what you'd have to do to change the frequency. In general though, wave signals aren't the easiest to change, unless it's like a pulse-counting system, which might be easier.
That might be what I have to do. Theres systems out there for about 100 bucks that will correct the speedo (speedohealer....) but I dont want to pay for something I can/should be able to figure out. (Im in the middle of finals and finishing sr design, I will be insanely busy for the next few days, and then freee till work starts, so well see what i can get accomplished in between)

Im pretty sure its a counting pulses its a square wave. ... from the service manual
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Old 05-11-2007, 05:47 PM   #10
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**** that, I like knowing how fast I go$$$$ PLust the speedo and RPM are all on the same board it will display an error where the MPH is usually.... annoying!
Most bikes the tach will still work fine and the speedo will read 00.
In your miata, you can look at the tach and see 4k rpm, then know you're doing 80 w/o looking at the speedo right? You can do the same thing on a bike. You'll very quickly learn how fast you're going by feel anyway. I almost never look down at my speedo when riding; I don't have to. And if you're going so fast that you can't tell, you shouldn't be looking at the speedo anyway.

Anyway, if it's PWM based, you can build a comparator circuit inexpensively.

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Old 05-11-2007, 06:07 PM   #11
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buy a better bike like an aprilia that uses a sensor on the rear brake.
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Old 05-11-2007, 06:20 PM   #12
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buy a better bike like an aprilia that uses a sensor on the rear brake.
Haha thats so much simpler
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Old 05-11-2007, 06:28 PM   #13
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Originally Posted by Ben View Post

Anyway, if it's PWM based, you can build a comparator circuit inexpensively.

Ben
Thats what Im trying to figure out.
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Old 05-11-2007, 06:41 PM   #14
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One option would be a frequency-to-voltage converter, an op-amp, and then a VCO.

You didn't say whetehr it reads high or low. If it's reading high then maybe you could just build a simple divide-by-n circuit, something as simple as a shift register and a big multi-input AND gate to drop every nth pulse?
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Old 05-11-2007, 06:47 PM   #15
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Its reading high, ie it reads 42 mph when im really going 38.5 mph.

I like that drop every pulse.
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Old 05-11-2007, 07:00 PM   #16
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most people don't worry about it, i kept my sprockets stock, any more aggressive and it will stand up even easier
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Old 05-11-2007, 08:55 PM   #17
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So how do i drop a pulse?
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Old 05-11-2007, 09:46 PM   #18
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get a simple PIC microcontroller (16F series for example) and write a simple program to take counts in (on an interrupt) and use a variable to drop as many counts (or as little) as you want. Make sure you scope the signal beforehand and do some signal conditioning circuitry before the PIC input as it is a 0-5volt and current must also be watched.

The whole thing won't cost you more than a few dollars if you already have a PIC programmer and know some basic C (you need a compiler for that) or assembler.
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Old 05-11-2007, 11:58 PM   #19
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BTW most sport bikes are 10% fast from the factory, so you went what, + in the back and - in the front? It'll probably be more accurate now than before.
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Old 05-12-2007, 01:08 AM   #20
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Quote:
Originally Posted by Lex View Post
get a simple PIC microcontroller (16F series for example) and write a simple program to take counts in (on an interrupt) and use a variable to drop as many counts (or as little) as you want. Make sure you scope the signal beforehand and do some signal conditioning circuitry before the PIC input as it is a 0-5volt and current must also be watched.

The whole thing won't cost you more than a few dollars if you already have a PIC programmer and know some basic C (you need a compiler for that) or assembler.
I need way more info than that. Im a M.E. my knowledge of electrical stuff is based solely on resistors and ...well thats about it.
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