Subject: Digital Speedometer

[Gerald Pelnar]

Joe Wrote:

> Lest, I digress. The original question was about a
digital speedo. If it is
> on a car, 4 small magnets can be epoxied onto the
driveshaft 90 degrees
> apart. Then use a Hall effect sensor mounted on a bracket
in line with the
> magnets. This is your speed pickup. It's easy to
calculate the pulses/second
> for a given speed knowing your tire diameter and gear
ratio. Then you just
> need to count pulses for a set time period and then do a
little math to give
> the speed directly. If you use some high brightness seven
segment LED
> displays, you can get a pretty good reflection on the
inside of the
> windshield. You have to mirror the display once before it
is reflected off
> of the windshield so it reads unmirrored.

You could wire the 7 segment displays to read upside down.
They would read properly reflected once.

Gerald Pelnar
wd0fyf at mpks.net
McPherson, KS
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