Hi, gang. For the train guys out here, I'm working on juicing a frog on a DCC layout.
For those who saw that as greek, sorry. I need to reverse the polarity of a piece of track.
My first thought was a pair of non-latching relays that the Arduino would flip as needed. Then I wondered can a relay work backwards. eg, NO and NC are the input, and the COM is the output?
Again thanks. I'm way more of a programmer than I am an electronics guy.
Whilst I freely admit that I know practically nothing about DCC train control, why do you need to reverse the polarity of a section of track ?
I thought that one of the features of DCC was that the track voltage was constant and that the locos were controlled digitally
I would think a DPDT relay would easily do the job. You can do it with semiconductors (Google H motor driver) but would be much more work / complex.
Excellent question.
In a turn out where the tracks all cross there is a small piece called a frog. when a train is crossing the turn out normally, the right wheels contact frog. When it's following the divergent route, the left wheels contact the frog.
So depending on which direction the points are set, that frog has to have the polarity flipped.
Thanks JohnRob. I would use a manual DPDT switch for this before, and didn't know a DPDT relay existed. I'll go look it up.
Yes, it is perfectly usual to use a relay common to select between two alternate supply lines.
Generally you will control the relay according to which way the points are switched.
But it may be more appropriate for you to describe the layout in general.
I didn't see this until I read @Paul_B's post.
See this link showing a typical DPDT device wired for reversal. reversal wiring.
How are you going to throw the turnout? if you are using a servo and arduino then you can connect a relay and when the turnout is thrown it will trigger the relay. which can then change the polarity on the frog.
john
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