Does TIU backfeed watchdog thru fixed 1 input?

 Yes.

 The watchdog signal goes out on both the red and black output posts.

As an alternative you could use a variable output for voltage control and toggle on/off the DCS signal (including watchdog output) when you want to run conventional.  You can turn off the DCS signal under...

MENU / SYSTEM / DCS SETUP

So,

If I used a DPDT switch and used the other pole to switch the black between the Z4000 output and the TIU output to feed the track, the watchdog shouldn't get thru, right?

My problem with the watchdog on black concept is that if I power TIU fixed 1 with a different source, the watchdog doesn't trigger the conventional track.

This is what I set up on a friend's layout with power to TIU from Z4000.  DCS locos get watchdog even when track 1 is switched to conventional. It appeared to me that the watchdog was leaking out the F1 RED INPUT to the track via the common red connection to the Z4000

But this works on my layout, where I don't power the TIU from Z4000

I want a physical switch to select DCS/Conventional for each track, and I'm using the two variable track outputs (on/off-able DCS via remote) on the TIU for other things.

Ed

I'm confused why the WD on the conventional track is an issue.  It wouldn't be recognized by any conventional locomotive, right?

John,

I'm confused why the WD on the conventional track is an issue.

I expect because it would preclude running DCS engines conventionally with other conventional engines.

Yep, I guess I don't see the utility of having multiple conventional engines on a single power district in any case.  Besides, if I have a command engine, I tend to run it in command. 

WAIT, other than repairs, I'm pretty exclusively command, probably why I don't understand the utility.

Sometimes when kids are visiting, I run DCS loco in conventional.  Why?

I have wired pushbuttons around the layout for horn/whistle (DC offset) operation.  With the DCS locos in conventional, the kids can blow the whistles.  Seems kind of basic, but the kid love it!

DC offset remote whistle buttons don't work under DCS control.

Guys, do you think the watchdog could be backfeeding thru the INPUT to the TIU?

Ed

That explains it Ed.

Eddie, years ago I tried an experiment, and found it could get a usable DCS signal on the tracks by feeding the tracks from the input side.  So I would say yes, it can backfeed.  I'll leave it to the electronics experts to discuss whether it is possible to impose the DCS signal onto the FIXED circuit and not have it go in both directions.

The signal should not back feed to the "input" side of the TIU.  There are inductors on the TIU board that prevent this.  It's possible, of course, for an inductor to be out of spec and get some signal leakage, but I have never seen it in person on a TIU.  I suspect Ed is getting the watchdog signal looping around his toggle switch on the black output.  Using a DPDT toggle should isolate the watchdog signal.  If it doesn't there may very well be an inductor that is out of spec on the TIU. 

Dave,

I get what you're saying but this is the same situation on 3 different TIUS I've tried it on.

If a circuit needs 2 wires to pass a signal, and the red wire is broken by the switch, how could the DCS signal get by on only the black?  You use the work "looping", but that's hard to do without a loop,no?

Ed

"If I used a DPDT switch and used the other pole to switch the black between the Z4000 output and the TIU output to feed the track, the watchdog shouldn't get thru, right?"

The difference in your 2 diagrams is when using the Power House, the outer rail feed from the Z4000 is not going through the TIU. Wiring a DPDT switch would do the same thing as long as the outer rail feed is switched before the TIU input.

I work in the automotive field. Our early version of CAN B bus for communicating with other interior modules is a 2 wire system that is capable of running on one wire. Cut one of the wires and the modules still communicate and you never know it until you hooked up a scan tool.