# Circuit to detect reverse condition of an auto-reverse board



## wa2ise (Dec 1, 2013)

My club's layout uses a few of these boards:








And we have a computer we use for dispatching during operating sessions. And on that computer is a map of the layout with indications of block occupancy and block short circuit conditions. These reversing boards only have an output that tell if it's in normal (LED off), reverse (LED blinking) and short (LED steady on). At least I can't find anything more than this, even though I see optocouplers on the board. We inserted an optocoupler in the output line of this LED, and feed the output of the optocoupler to an ST board (sentry IIRC board with 16 TTL level (0V or 5V) inputs). Thing is, the computer SW we wrote can't really tell between "reversed" vs "short" indications. The blinking goes too fast for the polling rate of the computer. As far as I can figure out, the reverser board has no independent short or reverse output. 
So I rigged up this below circuit to detect a reversed condition. Connect one of the two input wires, and the corrosponding of the two output wires to this circuit, and if the board is in reverse mode, the circuit's LEDs light up. And sends a low signal to the ST board and computer. If there's a short, this circuit should go dark, and thus send a high signal to the ST board and computer, as the reverser board goes open circuit and not pass any current thru this circuit. We use Yellow wire for the "hot" side of the DCC supply system, and green wire for the "ground" side (the "hot" side we have all the circuit breaker boards disconnect in case of a short). 








Assuming this always works, the computer SW can use simple logic to tell shorts from reversed conditions. It might make a difference which wires I use above on the reverser board, so I might need to connect to the "hot" (our yellow) wires.


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## DonR (Oct 18, 2012)

Very interesting circuitry.

But, Why does one need to know the 'reverse condition' of an isolated section?
The reverse controller will do a phase match automatically when the first
metal wheels span the insulated joiners.

Don


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## wa2ise (Dec 1, 2013)

DonR said:


> Very interesting circuitry.
> 
> But, Why does one need to know the 'reverse condition' of an isolated section?
> ...


Our computer SW we wrote can't really tell between "reversed" vs "short" indications. So we needed another signal that says "reversed" so we can tell for sure when a short happens. And the reverse signal goes away when a short happens. "It's a short when (reverse or short) is on and the (reverse) is not on." If it is a short, we flash a warning on the appropriate track on the computer's map of the layout.
I found my circuit works fine on the DCC "ground" wires.


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