Is there such a thing as a Pressure Sensor?

[Anonymous]

I bought a rail crossing for my 3 rail O-scale Lionel track.  I thought there was something that sensed when the train went by that would trigger the crossing - but the only thing I see for sale is an expensive infared system.  I'm looking for the old-style (cheaper) pressure track.  Does anyone know where I can find this??

Thanks in advance. 

[Curmudgeon]

Oh, man, you made me think back longer than I wanted.

 

152 contactor, I think.

These are long, older ones all metal, screw tension adjustment.

They should be quite plentiful I may even have some still. I'll check.

 

TOC

[Curmudgeon]

153C.

 

EDIT:  George Tebolt lists them at $8.50.

 

Here's the linque:

http://georgetebolt.com/postlist.html

[Puckdropper]

You can make a simple one with a few parts.  The basic idea is a contact gets moved by the train and connects with another contact.  When the train passes, the connection is released.  How you do it is up to you, a spring or counterweight should be easy enough.  (The counterweight would work like a teeter-totter.)

[Curmudgeon]

Actually, it's even easier.

Pre-war, they insulated one outer rail from the metal ties (same center rail insulators), insulated pins at the ends.

The ground was made by the wheels shorting the outer rails together.

[ndbprr]

How sophisticated do you want it to be?  Transducers can be had to measure anything from micrograms to thousands of pounds.  Easist of all is the old Walthers track switch (I think that is what they called it)  Basically a piece of brass (I would use nickel silver today) adjusted so it did not contact the inside of the rail but close enough it would contact the backside of a wheel which completed the circuit to the rail.

[Anonymous]

I would just like to buy something that will switch the crossing on and turn it off after the train passes through.  Not really adept at making my own parts - that never has worked for me.

What do they use for a standard crossing today?  The infrared sensor?

 

[ndbprr]

I would use a pair of infrared transistors (they come in a package at Radio Shack as an emitter and receiver).  Mount them diagonally accross the track and hide them in a pile of ties so they can't be seen.  Mount them high enough so the body of the car blocks the beam and at an angle so the gap between cars doesn;t turn it off.  Hook the output to the flasher circuit and you are done.  This is a pretty simple application electronically and could start you into more difficult projects.  If mounting them outdoors make sure they are well into the pile of ties so sunlight doesn;t trigger the receiver.

 

[ndbprr]

There is another easy way to do this also.  Use a Cadmium Sulfide cell also available at Radio Shack to signal the flashing circuit.  As the train passes over it it blocks the light and can act as a switch also. 

[Curmudgeon]

If you want simple, buy a 153C contactor set.

What kind of track are you using?

 

In my day, we had no money for such things, we pulled one outer rail off, however many sections we thought we'd need for the crossing (like 5 before and 5 after), make insulator pads or rip apart old curved sections for their pads, install pads and rail, and an insulator pin at the ends, or a wooden matchstick.

 

Fixed power (or center rail power) to one side of the crossing, the other terminal to the insulated section.

 

As the train entered the section, power crossed through all the uninsulated wheels and axles across, and it worked.

The problem with an infrared sensor (unless you build in a delay) is when the caboose passes, the crossing stops, but you still have 1-5 cars to go.

 

Even a contactor does that.

This way you can have anything you want for length.

If using plastic tied track, just insulate the ends of one outer rail.

 

This is three-rail.

It is NOT rocket science.

 

TOC