fuel flow sensing

[Dave J. Andruczyk]

> Do you know how the Vehicle Speed Sensor works? I am currently working on

Some cars use the toothed wheel that the ABS system uses.  Some cars ( the
ones with ABS) use a toothed wheel mounted on  the axle stubs right behind
the brakes.  A hall sensor picks up the pulses.  

> a system that uses magnets fixed onto the drive shaft, and a hall effect
> transistor. The problem i have found is that the shaft tends to move
> around quite a bit (in relation to the rest of the vehicle). As i have
> mounted the hall effect device onto the underside of the car, it
> sometimese cannot sense the magnet becaues the drive shaft is too far
> away. I haven't had a second attempt yet (with longer magnets/stronger and
> moving the hall effect device closer) but i was wondering if there is
> some other way that i should maybe try.

I tried a similar approach when trying to make a a digital speedo.  I
ended up epoxying the magnets really close to the transmission on the
halfshaft. That way when thee suspension moves,  the moevement by the
tranny is rather minimal, and thus I could get a reasonably reliable
signal.

Dave