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Said another way, in a simplied example where there is only an AIU with a direct connection to tracks (that is, no intervening relay), the PBW would be connected to the inputs to the AIU and the signal is only received by the track that is connected when the AIU internal relay is energized.  In that example, and assuming no AIU relays are closed, and with the transformer having its handle engaged, the PBW would actively be generating a signal since it’s positive and negative is connected even though no tracks are powered.   

Correct.  If using just the AIU's ACC port relays, if none of the ACC ports are "ON", the PBW would be generating the blasting out the watchdog signal once per second...but no one would be listening!   Oh well.  There are bigger problems in the world!

Note that the AIU ACC port internal relays are capable of 3 or 4 Amps (something like that).  This should not be a problem for roundtable whiskers, sidings, etc. since you shouldn't be zooming engines with long loads like you might on a main-line section.  In which case you'd have the ACC port power an external $1 relay that can handle the "full" 10 Amps for a TIU channel.  

 

 

Just an update, I decided to go ahead with the 555 timer version as it has less parts and also requires no calibration.  So I built half a dozen and put one in my remaining spare DCS-RC box in case one of the ones on the layout ever craps out.

Of the half dozen I built, I only had a 3% variation in the time interval that they trigger, well within the tolerance needed to generate a reliable watchdog signal.  I didn't have one of the 1% resistors, they're trapped in COVID delays.  That being the case, I simply hand selected from a batch of 5% resistors using a 1% resistor as a standard to match them using a Fluke bench meter.  Most of the timing variation I see probably comes from the 5% capacitor, a .47uf 1% capacitor is price prohibitive, it cost more than all the other parts, including the PCB!

555 Timer Based Watchdog Generator Board

The three pin female socket mounts as illustrated in the three holes at the end of J2.

+

The WD board plugs into the female socket.

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I do a lot of SMD, this was laid out as a kit so I did it with thru-hole stuff as many people have difficulty with SMD.   For this application, there was no benefit to SMD, there's plenty of room for the board inside the DCS-RC where it installs.

I do have a size limit on hand assembled SMD, usually 0603 for resistors and caps.  They're still pretty easy to handle.  I once screwed up and specified some 0201 resistors on a board, I couldn't even see the little things!  It took me forever to build the prototype, and I immediately sent that sucker out for a rework with larger parts!

Most of my products that are sold through Hennings are SMD.  Also, most of the stuff I've build for local use here is SMD, only a handful of the projects end up being thru-hole.  If it might be offered as a kit, I look at thru-hole.  Also, if I'm going to hand assemble a bunch of them, I may consider thru-hole for at least some parts, it's usually quicker to do.

Chuff-Generator

Super-Chuffer II

LED Lighting Regulator

YLB - RailSounds Battery Replacement

Last edited by gunrunnerjohn

John, interesting comment on the 0603 smd size. With my limited (but growing) smd experience, thats pretty much the smallest size that seems practical. I accidentally ordered a few 0402 resistors a while back, and promptly tossed them out when they arrived.

I was happy to see that all parts for your smart motherboard project are at least 0603, and it went together quite nicely. I finally figured out an smd soldering technique that seems to get the job done with minimal muss and fuss. The only pesky part on that board is the tiny little indicator led, and being polarity sensitive, you need to get it right!

Anyway finally after all your prodding I took the smd plunge, and here we are. It seems to be working! Nice when an old dog can still pick up a new trick or two.

Rod

Nope, other than cycling power on the input of the TIU channels.  I obviously have the full TIU, but I also have three of the four channels being fed by my WD generator.  This allows me to switch individual sidings that are powered by these channels and not have to turn off the entire channel to insure a WD signal to keep the engines silent.

DCS-RC boxes at the top are all equipped with the WD board and service everything but the mainline TIU channel.

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You can buy just the DCS Remote Commander 50-1033.  The MTH site shows no dealer stock using "Find It Locally" though I'm not sure this availability info is up-to-date given MTH's evolving business situation.

There was a time a few years back when you could get the DCS-RC for next to nothing on eBay or from an OGR member.  Now I see they are selling for more than the $60 MSRP!

@mike g. posted:

Hi John, I am late to this game, but what if you don't have a DCS commander for your Watchdog timer board?

BTW, if searching be sure to use "DCS Remote Commander" and the 50-1033 part number.  MTH also made a "DCS Commander" which is a different animal.

mth dcs 50-1033 dcs remote commander on eBay buy it now

You only need the receiver shown on the left.  You don't need the remote.  Sometimes you will see an eBay listing for one or the other...though usually it's just the remote for sale.

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Last edited by stan2004

Nope, other than cycling power on the input of the TIU channels.  I obviously have the full TIU, but I also have three of the four channels being fed by my WD generator.

...

Seems I've read many threads over the years on guys with a TIU that only partially work, or too old to upgrade, or whatever...and are sitting in a box.  So if someone absolutely needs this power-on watchdog function, I wonder if the "next" gadget is some way to re-purpose an unused TIU (or even just an unused TIU channel) in passive mode for the sole purpose of generating the Watchdog?!

@stan2004 posted:

Seems I've read many threads over the years on guys with a TIU that only partially work, or too old to upgrade, or whatever...and are sitting in a box.  So if someone absolutely needs this power-on watchdog function, I wonder if the "next" gadget is some way to re-purpose an unused TIU (or even just an unused TIU channel) in passive mode for the sole purpose of generating the Watchdog?!

The problem with the TIU is connecting two channels together seems to create issues, I don't know how that would be resolved.

For some reason the DCS-RC in parallel with the output doesn't seem to cause a problem.   The only issue so far that's surfaced is the Apple version of the DCS WiFi app has issues adding engines with the WD generator active.  However, the Android version here has no issue at all with the WD generator running on the channel.

The problem with the TIU is connecting two channels together seems to create issues, I don't know how that would be resolved.

For some reason the DCS-RC in parallel with the output doesn't seem to cause a problem.   The only issue so far that's surfaced is the Apple version of the DCS WiFi app has issues adding engines with the WD generator active.  However, the Android version here has no issue at all with the WD generator running on the channel.

Of course this is all in the spirit of OGR being a discussion forum.  That said ...

I think the trick would be to power up an unused/available TIU channel for a just a few seconds and then remove power....just long enough for the TIU channel to generate its power-on Watchdog.

As briefly discussed early in this thread (which is almost 5 years old!) I'd still push for a "solution" that does not require the user to rotate the switch to the "home" position each time changing the active yard track.  So it would be some kind of change detector that then activates a timer that applies track power for just a few seconds to an available TIU channel in passive mode.

@mike g. posted:

Stan and John, thanks for the information. so with just 2 sidings that I power on and off can I do that with one DCS box?

Yes, I manage six sidings on one TIU channel, each siding has an individual power switch, all are powered from that single channel.   I also have sixteen turntable whisker tracks and my access loop for the turn table on one TIU channel, each whisker track is individually switched when I want to access the engine in that location.  The sky is the limit really.  Most of the channels will be off and not affecting the DCS signal as a rule.

@stan2004 posted:

Of course this is all in the spirit of OGR being a discussion forum.  That said ...

I think the trick would be to power up an unused/available TIU channel for a just a few seconds and then remove power....just long enough for the TIU channel to generate its power-on Watchdog.

As briefly discussed early in this thread (which is almost 5 years old!) I'd still push for a "solution" that does not require the user to rotate the switch to the "home" position each time changing the active yard track.  So it would be some kind of change detector that then activates a timer that applies track power for just a few seconds to an available TIU channel in passive mode.

You're right Stan, that was also part of that discussion.  Remember this diagram?  This was an effort to do exactly that, just connect the TIU channel in passive mode when one of the yard tracks was activated.  With a break before make rotary switch, the thinking was each track change would break power for long enough to force a reset of the channel and another WD instance.

You scuttled this whole scheme with the clever WD reset board for the DCS-RC, that ended up being such a much better alternative that I abandoned thinking about doing it with a TIU channel.



...With a break before make rotary switch, the thinking was each track change would break power for long enough to force a reset of the channel and another WD instance...

Wow, I can almost remember the discussion after 5 years...yet I had to think hard about what I had for breakfast.

I'd be surprised if the break-before-make interval is long enough to trigger a new power-on reset.  Additionally, the donor TIU channel would then be ON.  It is my understanding that later versions of TIU would "spray" Watchdog activity for tens of seconds when a channel is first turned on.  So during this time, and to your earlier point, having the passive channel spray watchdog activity for many seconds might interfere with the mainline's TIU channel performing normal DCS control.  Hence, I believe the prudent thing to do is to only turn on the Watchdog channel for a few seconds at most.

Putting the cart before the horse, but if we were in a parallel universe where there was no such thing as a DCS-RC...and we were pondering how to use an unused TIU channel...the tactical decision is whether to have a relay clicking On/Off once per second.  This would be the PBT or Perpetual Barking TIU.    OR, come up with some "change detector" and timer scheme to briefly passively power the spare TIU channel only when a new yard track, roundhouse spur, siding, or whatever is powered.

Last edited by stan2004

Paralleling the outputs of the TIU is bad news.  I'm not sure what would happen with that second channel camped on the output of the powered channel, but my spidey sense tells me that could be trouble.  You need to disconnect the second channel from the yard track, it couldn't be sitting in parallel as you'd simply be powering that  channel passively from the yard track.

I suppose you could see if you could capacitively couple the channel and then just hit the input with the brief power shot...

My vote is still for the $50 solution I found buying the DCS-RC set in the earlier post.

Paralleling the outputs of the TIU is bad news.  I'm not sure what would happen with that second channel camped on the output of the powered channel, but my spidey sense tells me that could be trouble.  You need to disconnect the second channel from the yard track, it couldn't be sitting in parallel as you'd simply be powering that  channel passively from the yard track.

I suppose you could see if you could capacitively couple the channel and then just hit the input with the brief power shot...

My vote is still for the $50 solution I found buying the DCS-RC set in the earlier post.

John what is the DCS-RC you are referring to?

No, TMCC/Legacy doesn't have the same design, thus that signal propagation is much different.  It's not to say you'll never have issues with TMCC/Legacy signals, but they are typically manifested with larger layouts, and especially multi-level layouts.  TMCC/Legacy also doesn't have the concept of a watchdog signal, the TMCC signal carrier is constant on the rails.

Last edited by gunrunnerjohn
@Dougklink posted:

Thanks John.  I need to understand tmcc/legacy better.  Wish there was something like the dcs book for it!  Have I missed that?

Not sure these are as detailed as Barry's DCS book, but here is something for TMCC/Legacy - Book & DVDs from TM Books.

Might be worth a look?

Direct link above didn't go directly to the items. From the above link search for  -  Modern O Gauge Remote Control at the TM Books site.

Last edited by rtr12

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