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post #19 of (permalink) Old 04-17-2017, 08:30 PM Thread Starter
3rd Gear Poster
Kenz's Avatar
Join Date: Oct 2014
Location: SYR, NY
Posts: 146
Originally Posted by RalphP View Post
Here's a wild idea.

For under $10, if you have the time for ship-from-China, you can order a function generator kit.

Assemble it.

Then, doing the math ( 8,000 pulses per mile, 60 seconds in a minute, so 133.333 pulses/second = 60 MPH - use other frequencies and solve the other way for way points on the speedo! ) you can adjust the needle on the bench, no "Let me plug this in while doing 60MPH in traffic!"

Takes a 9V battery or so for the function generator; use a full 7805 instead of the small 78L05 the kit comes with, heat sink it, and you can drive it, and the speedo, off a 12V power supply or battery.

I find this a LOT easier.

Oh, and crank it to about 260Hz on the function generator, and you can get about 120MPH to bring the odometer up to the proper setting *grins* Just be aware that it takes about 8.5 hours to run 1,000 miles, so about 3,000 every day approx; if you're about 120,000 off that's an easy 45 days of it just sitting there running.

Thanks for the help with this. I never would have thought calibrate it this way, found out I had the needle set 2MPH too fast after putting it back together. I'm lucky and have a EE in the family to help me out with this as well.

This time I twisted the needle and it came off very easily. I just twisted it back and forth several times, then it popped right off with the use of a fork. Replacing the gears was actually pretty straight forward, so was adjusting the odometer. It is a very simple unit, you can tell it is evolved from a cable driven design.

Pardon the mess in the picture. Kind of threw everything together in a spare room...
Attached Images
File Type: jpg speedo (Small).jpg (85.2 KB, 2 views)

96 Cougar Sport
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