>Joshua Van Tol wrote:
>
>> >Why not make your own fifth wheel? As you wrote, you can roll it 100
>> >rotations and
>> >get the accurate distance. Here is how I would do it: first, make a
>>frame that
>> >attaches to the car, then a fork with a pivot and a bicycle wheel, a hatch
>> >strut
>> >to give it an even pressure to the ground, and a bicycle speedometer. These
>> >speedos can be programmed to fit the circumference of the wheel, by the
>>exact
>> >millimeter. The only drawback is that you would have to mount it close
>>to the
>> >driver or passenger seat, because the bike speedos don't have too much
>>wire.
>>
>> If you wanna go to this much trouble, surely lengthening the cable wouldn't
>> be too much trouble? They're just two wires in a heavy duty sheath to
>> prevent abrasion.
>>
>> Joshua Van Tol -- jjvantol@lear.csp.ee.memphis.edu
>
>The only worry about lengthening the cable is that it might screw up the
>magnetic
>impulse from the sending unit

The bandwidth isn't nearly high enough to matter, even if they are hall
effect sensors, or some similar type of sensor. Use sheilded microphone
cable if it worries you.

Most (all that I've ever seen, but who knows?) of these are not hall effect
switches, as you might assume, but plain old reed switches, which work just
fine at bicycle speeds.

Joshua Van Tol -- jjvantol@lear.csp.ee.memphis.edu