Shutoff Circuit

All you really need is a micro switch which trips open when the gate is ajar.,perhaps hooked to a relay that shuts off track power or power blocks on the approach when the walk through is open. If you make outside insulated rails on the approach you could have a warning light or block signal as to when it is safe to open the gate. The relay could be powered by any unused tap of a track transformer 10 volt or 18 volt.

Really not that complicated. There is nothing pre built I know of. looking at maybe $10 for parts.

Dale H

OK, for a mostly mechanical cutoff:

Make isolated sections in the tracks approaching the bridge.

Run the power to them to a contact under the bridge which touches a mating contact on the bridge itself.

Make a small loop of wire on the bridge and connect to a second contact. The second contact mates to the track on that end of the bridge.

Do this for both ends.

When the bridge is out no power can get to the tracks approaching the bridge and the trains stop.

Search eBay for "lever micro switch".  All kinds of styles - lever lengths.  Here's an example that goes for $1 shipped.  15 Amp contacts.  Used for appliance (oven, dishwasher, etc.) electrical power cut-off when the door opens so essentially same application as your bridge out.  The lever itself has "flex" which relaxes mechanical tolerances in mounting. Uses standard slide-on (e.g., Faston) connectors used everywhere.  Switch cuts power to track section before bridge ; at $1 each, a switch on each approach shouldn't break the bank.

This lift bridge video will give you an idea of the mechanical and structural set up. It also shows the microswitches connected to the relays to cut power. The bridge sits on the switch when in place to power the relay which then powers the isolated track section. The lift out harness is connected using Anderson Power pole connectors. Info on the locking pins is in another post. Let me know if you want more info on those.

Thank you for all the comments. Seems straight forward...but I'm likely to have some more questions once my micro switches come in.

Thanks again everyone!  Terry

Be aware that if you are running DCS or TMCC, when power is re-applied, the engines will come up in conventional mode not command mode. There is a work around for the DCS (not sure about TMCC) where the power is removed going into the TIU channel and its output goes to your isolated track sections.  When power is restored, the TIU sends out its watchdog wakeup message again to the engine(s) putting them into DCS command mode.

In reality it's best to kill the power to the loop (if it is a loop) of track that has the bridge in it.

I only say this because, while there is only a small chance of this, a train that has passed through the bridge will likely have the engine positioned beyond the isolated track sections which are near the bridge. With the loop still hot outside of the isolated track sections nothing will prevent an accidental backing up of the train pushing the caboose and other cars into the chasm.

This is purely worst case scenario but it could happen. De-powering the entire loop would prevent this.

Mark

You could use an outside insulated rail of each loop in the section where it goes through the gate. This could power a red light as a warning not to open the gate. You could even use a relay and a solenoid to lock the gate down to prevent it form being lifted when the blocks are occupied. This would work in either train direction. I would also put a delay on timer which would delay power restoration so the operator could inspect gate latching and alignment before the train resume.

Dale H