Combining Lionel BCP2 with MTH DCS

Hopefully someone more knowledgeable about DCS systems will reply.  Here's what I think I understand regarding your question about controlling a Lionel BPC2 with the new MTH WTIU.  I've only recently purchased and read the DCS Companion 3rd Edition (suggested reading).  It says that the older TIU was at that time only capable of controlling TMCC engines with the correct setup, but not capable of controlling other Lionel LCS devices, including switch tracks and accessories.  Instead, Barry Broskowitz recommended using the MTH ASC to do this.

The correct set-up at that time for allowing DCS control of TMCC engines was essentially TIU Serial out to the serial port on either the Lionel TMCC Base), Base 1L, or Base 2.

Such a hypothetical connection for Base 3 would be TIU serial out to LCS Ser2 to Base 3.

However, with the WTIU, last I heard, MTH has not yet offered a compatible serial cable, and even if they have, the WTIU may or still may not be able to control a BPC2 like it's TIU predecessor.

As I understand it, your Command options for controlling power to blocks are either using the [ MTH AUI controlled by the WTIU via the DCS app ] or with the [ BPC2 connected to your Base 3 and controlled by either the Cab 3 app, Cab 2, or a Cab 1L ].

There are a couple of other possibilities being developed by a few individuals, but that's another subject.  Hopefully someone else will chime in here.

If you are using an iPad to throw the turnouts, why not use the same iPad to turn the track block power on and off with the BPC-2? That would be the simplest solution. Is there a reason the plan is to use the iPad for ASC-2's and not BPC-2's?

I assume you are aware that an STM-2 is required for turnout position reporting in addition to the ASC-2 when an iPad is used.

DCS fundamental rules- because that is what shapes your decisions.

The WTIU and the TIU before it- both ONLY generate a watchdog signal when a channel is first powered (as seen on input or output of the channel- then the channel sends the watchdog)

So- now knowing that key rule- if you intend to use any form of control- not just the BPC- to example switch on a siding- in order to ensure a watchdog signal is sent so the MTH locomotive parked on that siding doesn't self start up in conventional mode- we have to ensure we send a watchdog signal.

So options to ensure that happens:

#1 use a WTIU channel for each siding. Ensure the BPC is on the INPUT to the WTIU such that when the BPC turns on that siding, the WTIU channel so that it is sensed a power state change- and a DCS watchdog is sent to prevent an engine from just starting up in conventional EDIT- to better make this clearer, the point I'm trying to make is that the WTIU channel must see the OFF/ON power state change, in order to then send a watchdog signal. It can be on the input of the WTIU channel, or the output- hence passive mode below. I just saying again, the arrangement has to be that something first "triggers" a state change to powered event on a channel- to then send a watchdog- hence if using a BPC to control power in this manner- the BPC is before the WTIU or in parallel, but not after. As an example- the WTIU channel is powered, and then the BPC is directing the power ON/OFF to the siding- results in no watchdog being sent.

#2 A quirk known to exist with the new WTIU is there have been reports that power states and watchdog issues exist when sending power THROUGH the TIU from channel input to output and using the internal power control subsystem- there can be glitches. The current known workaround is to wire the TIU in PASSIVE mode. This means we ONLY wire the output of each channel to the track and separately put an inductor in each power source connected to the track. Passive mode no longer depends on power passing through the WTIU- and only uses the DCS signal generation capability- which thus far has proven to work better in passive mode.

#3 in combination with the above, some have used a break before make setup, and possibly in conjunction with the perpetually barking watchdog generator- a modified IR DCS commander with a reset circuit causing it to send watchdog signals for siding like this.

Just to be clear- the BPC is a very simple device and not really the cause of any of this, nor is LCS.

The question you are really asking (without knowing it) is that there are now a bunch of rules and best practices specific to DCS and the WTIU usage.- that further got complicated by the new WTIU and some limitations and problems people have seen with it (the whole passive mode workaround). This is further complicated again, by the typical want to have a bunch of siding that you could turn power on or off any number of ways- toggle switches, relays, BPCs, the AIU, but the complication is ensuring that all important watchdog signal is sent just after power is turned on to prevent an MTH engine from starting up and worse- with power blips taking off top speed in conventional. It's this topic that others have dealt with and the same solutions in the past with the TIU mostly apply to the WTIU.

Thank you both for the responses. I think I was unclear...I do plan to use an iPad running the LCS app to control both switches and blocks, and connect the BPC2 and ASC2 via PDI cables to the Base3.  My concern was where to wire the BPC2.  I am assuming from a power perspective, that I need to run track power from the WTIU to the BPC2, and then on to the tracks, for those blocks I wish to be able to control via the LCS app.   For the mainlines that will always be "on" I assume I can just wire directly to them from the WTIU?

Regarding the STM2, I thought for tortoise switch machines only the ASC2 was needed, but what's one more electrical component under the table!

Since I am only using legacy I forgot about the watchdog signal. Vernon outlined the issues and choices for the solution.

The STM-2 is what reports to the iPad LCS app the turnout position. This is needed when the layout is powered on, if the turnout is thrown from a handheld, or if more than one iPad is in use. I use almost all Tortoise machines, just four DZ-2500's on a viaduct. I used an 18VAC supply and steering diodes to operate the Tortoise motors as described in their instructions. Been working great for 8 years so far.

Well, the obvious solution to the missing watchdog signal is to round up some MTH DCS Remote Commander boxes and stick my little WD Generator board in them.  This is connected to any power district and generates continuous WD signals for as long as there is power on the track it's connected to.