[sdiy] OT: TTL logic, trains and interference

[John L Marshall]

Wow!

What a cool hobby. I have always been facinated by trains. Where I grew up
(Walnut Creek, CA) the Sacramento Northern Line ran past my back yard. The
train was electric as the Milwaukee was.

I have a great collection of photos of 700 which lives in Portland, OR.

I was a member of the Sumpter Valley Railroad for a while. I have great
photos from there too.

I will build a web site and post the photos.

How do you get permission to use the right of way?

Where are the motorcars available?

Is this a club?

Fill me in.

Have you ever seen the three wheel cars? They look alot like a motocycle
with a side car.

It is bad news to run sensors directly into TTL without some signal
conditioning. There are TTL ICs that have Schmitt-trigger inputs such as
74??14. The schmitt-trigger will help with false triggering. You might want
to add a little low pass filtering, a resistor and capacitor, to the input
as well. The ultimate would be to use a differential input. This is probably
more than necessary for you.

Can you believe that several Super Ferries were built and put into service
in Puget Sound (Seattle) that had microprocessor controllers (6809 in one of
them) with no input conditioning or buffering. There were long lines
(hundres of feet) directly into the TTL. The system failed was immediately
ripped out.


----- Original Message -----
From: <nss at hevanet.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, August 16, 2001 4:21 AM
Subject: [sdiy] OT: TTL logic, trains and interference


> 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
>