Here are some pictures of the
device I built:
You can see the small button magnet in the
top block and the electronics that go into the small hole in
the bottom block. When I am happy that all is working
correctly - I pot the magnet and the electronics with epoxy
resin, so they stay in place and are water proof.
Here you can see the sandwich arrangement -
with the slot for the carbon steel vane to pass through.
Here is a proto type that I had assembled -
showing galvanized steel vane and hall effect sensor. This
vane has only 4 blades but a 5 blade vane gives the most
accurate mph value from the ECU (closest to Subaru VSS pulse
This is a finished VSS sensor with mounting
for an automatic tranny. wires to 3 pin connector are:
- Ign On.
- VSS signal
It generates a nice clean 0 to 5 volt
square wave when the vehicle is moving and there is no worry
that the Hall Effect sender is going to wear out.
The circuit is very basic - 1K resistor
connected to Ign On and the other end connected to the anode
of a 5 volt zener diode. The cathode of the zener is
connected to ground.
The Allegro A3245EUA
is connected as follows:
- Pin 1 - VCC goes to Ign On
- Pin 2 - goes to ground
- Pin 3 - is your VSS signal
and it connects to the junction of the resistor and the
This is the final arrangement that has been
running in my 86 Vanagon for the past few months. It has
worked very reliably and my Check Engine Light only comes On
when you first turn the Ignition Switch to the Run position -
it never comes on with the engine running.
Please let me know what you think of this arrangement -
comments good or bad are welcome
NOTE: Use these ideas at you own risk - no warranty or
guarantee implied or included. Tom