Hall Effect Gear Tooth Sensor

[A.DENNISON -EN320/TEL.8296]

On Wed, 4 Jan 1995, Jim Pieronek wrote:

> Can anyone give me a source for a Hall Effect Sensor for detecting 
> the teeth on a ring gear?  Any advice or experience on mounting and 
> using such a sensor would be appreciated also.

I would use an inductive pickup.  These are used on most EFI cars and are 
also available from other sources.  These sensors produce an AC signal 
which you could interface to a uP with an NPN and a few resistors:

               VCC
                |
                \
                / Rc
                \
                |---- To uP input 
       Rin      C
     -/\/\--- B     BC548, etc.
   |        |   E
   |        |   |
 Sensor Cb ---  |
   |       ---  |
   |________|___|
       GND

The RC time constant on the input filters out some sensor noise.  All 
values are arbitrary. Try:

Rc  = 4k7
Rin = 10k
Cin = 0.1uF

You could use a comparitor with hysteresis if you want but this should work 
OK.

You can interface RS232 in the same way if you want if you don't want to 
waste space on a MAX232 and associated caps.

I hope this helps....
Andrew
------------------------------------
Andrew Dennison - Research Associate
The CIM Centre
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