Turntable Polarity Indicator

[Flangehead]

I would like to build a polarity indicator for my scratchbuilt turntable. I use a DPDT switch to make the polarity conform to the exit track as usual, but I would like to know whether the polarity needs to be switched before the engine crosses the gap to or from the table rails. The indicator preferably would be a set of lights in the control panel

Any suggestions?
Thanks in advance y'all.

 

[Clerk]

I see where you are comming from Flangehead. Nothing like trying to run an engine onto the turntable and have it buck back because the current is the wrong way.
I would be interested to if somebody could come up with something. I do have a vauge idea but my memory won't come through

 

[Arlaghan]

Hmmmmm...

Now... I'm no electronics guru... in fact, I get all my information from my brother, but here's my idea and maybe someone who knows more can step in and fill in the blanks:

According to big bro' a diode is like a one-way thingy for currents to flow. Why don't you do something like put two light bulbs, say a red one and a green one. Then on one side of the red one, put a diode, and do the exact opposite to the green one. This, in theory would only have one light on depending on the polarity.

Then... one side of your turntable is "enterable" if the green light is on, the other side is "enterable" if the red one is on.

Gosh I hope this is true! LOL

 

[Clerk]

HEY! That would work. Also put the diodes on the track leading to the turntable and that would tell you which way to turn the current.

 

[jon-monon]

A standard red and green LED with a 1K resistor should work, adjusting resistor size for brightness. They can share the same resistor or use two seperate ones, either way is OK

 

[jon-monon]

 

[Clerk]

Thanks Jon. That will do it just fine.