[sdiy] OT: TTL logic, trains and interference

[nss at hevanet.com]

Sorry for the ot post, but I think this is my best bet for advice! And
it is DIY! And I know there are train freaks on the list...

anyway, I have an old railway motorcar
(pictures: http://www.hevanet.com/eths/railcar/railtext.htm) 
which I made a speedometer and odometer for. The odometer is made from
ttl ls chips and runs off a hall effect sensor which picks up the
gearteeth on the drive axle. The car has an automobile style electrical
system.

The problem is, the wire to the sensor pick up stray signals from the
ignition system. They are not nessisarily false triggers, it just kinda
drives some of the chips nuts. It is not from the power supply, as it
still does it when plugged into a bench supply. Picks it right out of
the air(as far as I can tell). Resistor plug wire and a cap on the coil
helped loads, but it needs a little more.

Any ideas???

Would a ferrite bead/ring be somthing that would help out here? I
suspect it is very high freq stuff...

Thanks for reading and any suggestions!

you never know, might want to use that synth in your car someday...

-Al Fisher