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Mr Stumpy

Joined: Sat Nov 2nd, 2013
Posts: 138
I ran across a way to automatically stop a train at the end of a point to point layout using diodes across rail gaps. You then throw the reverse switch on the power pack and the train runs the other direction until it comes to the diode at the other end.

Point to point without having to watch the train constantly, and it can run into a tunnel or building at the end of the line and stop safely without becoming wreckage on the floor.

Are there different diodes for different voltages? or could the same diode be used for both On30 and G scale?

Where would I find them? (The last operating Radio Shack in the region no longer deals in parts, but just sells cell phones and R/C toys.)

Since I'm not into electronics, DCC, or R/C on my micro layouts, this seems like a simple way to handle point to point operations while being distracted at train shows.

Stumpy in Ahia:old dude:


Joined: Tue Jan 24th, 2012
Location: Spring Branch [north Of San Antonio], Texas USA
Posts: 305
Bachmann makes what you are looking for in On30 and at one time there was one for G Gauge, I think Aristocraft.

If you want to build your own for On30 1n4005 diodes should work. For G Gauge what locomotive do you plan to use and what is it's current draw?

There are several online places you can get what you need. Are there any electronic supply places in your area?



Joined: Sun May 27th, 2012
Location: Missoula, Montana USA
Posts: 1000
Diodes operate like a one way valve, allowing electricity to flow in one direction, but not the other.

I believe most parts have a voltage rating. I'd go to a circuit store or an electronics store rather than radio shack anyways, they know cell phones, but they don't know electronics (at least that has been my experience). I'd check the labels on the diodes and pick up about 12 or so.

Also, Amps need to be considered. Amperes in G scale can reach 5 amps for one locomotive while in HO scale, you could run a 5 engine consist and barely touch 5 amps.

Since diodes are essentially a one way resistor, the diode will step down the current a certain amount, and thus will have a certain "maximum" voltage the diode can take. However, assuming the diode acts like a regular resistor, there is no minimum voltage.

So if it works for large scale, it should work for all smaller scales, but a small diode on an On30 display may not be big enough for large scale.

Here is a link to an article which explains the details well:


Last edited on Wed Jan 1st, 2014 03:50 pm by jtrain

W C Greene

Joined: Fri May 4th, 2007
Location: Royse City, Texas USA
Posts: 8254
CIRCUITRON also makes a great auto reverser module which has adjustable timing. I believe it is the AR-2 model and works on photo cells. I have used these on point to point display layouts for years without any problems.



Joined: Wed Jul 18th, 2012
Location: New York USA
Posts: 826
Don't be fooled by the amperage draw on HO scale. I have Athearn GP-39 that will draw 5 amps stalled.


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