Hi folks,

Got a question for those of you who are familiar with the lightbulb trick as it relates to the DCS signal and consistency of track power in general. I'm planning a new layout with a number of sidings. Barry's DCS Companion Guide strongly recommends placing each siding in a block with a lighted bumper and SPST toggle switch. The toggle switch is there to reduce power consumption when there is lighted rolling stock on the track, and to also prevent needless power-on time on command-control engines. The lighted bumper is there to help keep consistent track power and hopefully maintain a DCS signal strength as close to 10 as possible.

I'm wondering... if I went with a lighted SPST toggle switch (maybe like this: click here), would that kill two birds with one stone such that I may not need a lighted bumper? I can't think of why not, but I figured I'd ask the braintrust first.

Thanks guys!

Rafi

Original Post

You probably won't need any bulb with a newer version L TIU. If you use the older model without the USB jack, then you may need the bulb or filter.

I have found that the bulb should draw a decent amount of power ( >.1x amps ?) to clean the signal. If the bulb doesn't draw enough, it won't do much for the signal. If it draws too much, it's a waste of power. That's why some of us were excited to use Susan's filters before the release of the version L TIU. They don't draw much of anything. They do a great job on the signal.

" on Sour mash and cheap wine " ??

Why go back to DCC when I have DCS!

Hi Joe, thanks for the quick reply.

My two TIU's are older models (no USB port, not rev L).

That's a great point about burning out the lighted switch. This is an area where I'm a novice, but in the case of the switch that I linked above, it says it's rated for 125 VAC, and that the bulb pulls 12VDC. Would the bulb or the bulb's wiring in the switch burn out in that scenario? I'd be pushing 18V from the transformer in this scenario. 

If lighted switches won't pull enough power, or if they'll just burn out, I think I may have to hunker down and build a bunch of filters per Susan's schematics. Hopefully it's not too complicated!

Thanks again!

Rafi

I missed that point!

You can supply the bulb with it's own lower voltage power source. 

Susan's filters are pretty easy to build. I made a half dozen before I went to newer TIUs. Otherwise, I would have made more.

" on Sour mash and cheap wine " ??

Why go back to DCC when I have DCS!

Here's the details on the filters from the source.  These are a much better alternative to light bulbs, and they never burn out.

Filter for MTH-Controlled (DCS) Model Train Layouts

BTW, there's nothing "magic" about the "magic light bulbs", it's simply providing a signal termination to what is essentially an RF transmission line.  Think back to the old days of coax providing video signals, every run was terminated with a terminating resistor to minimize reflected energy that results in standing waves on the wire and corrupts the signal.  The filters described in the link above do the same job.  FWIW, they actually do use some energy, just not nearly as much as a light bulb.  If they truly used no energy, they also wouldn't do the intended job.

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