DCC Block Detection

Puckdropper · 2009-04-15T22:59:39+00:00

Our club layout has a few block detectors scattered around. They're made by Integrated Signal Systems. Does any one have a instruction booklet for these? I want to know how they're supposed to be installed. It looks like the fellow who installed them put them in one feeder to the block, but left the bus alone.I've observed an interesting behavior where the signal in front of an approaching train changes before the train crosses in to the next block. There's a good 15-18 inches before the signal when it changes.The parts of the signal system I'm referring to are here:

Apr 15, 2009 25 Replies

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Puckdropper 17 years ago

"Bob May" wrote in news:WoSdnUgyCMasxXfUnZ2dnUVZ snipped-for-privacy@o1.com:

I wish I could tell you more about what the detector is doing itself. All I've bothered to look at is there's a couple diodes and a LM324 IC (I'm fairly certain it's a LM324). Sure sounds like the Twin-T style as described here.

I've found a schematic for a detector that uses a coil and wire loop as PV described above. It doesn't look like it'd be more than about $10 each to build (probably around $5 in quantity), and senses down to a few mA.

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Puckdropper

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Puckdropper 17 years ago

pv+ snipped-for-privacy@pobox.com (PV) wrote in news:youdnQMIXuUCuHfUnZ2dnUVZ snipped-for-privacy@supernews.com:

Well, from the looks of it their website has been neglected since 2007. IMO, it would be worth half a day's work to update it and finish the electronics page descriptions. Uploading manuals would be great too.

Puckdropper

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Bob May 17 years ago

Yep, you've got the standard Twin-D (d for diode version of the Twin-T detector) design. Two of the op-amps in the chip (the LM324 which is a quad op-amp - 4 amps in one package) are used to detect in either direction the voltage across the diodes, one to combine the signal and the 4th to output the signal. When the current thhourgh the diodes gets high enough to produce some voltage, the circuit sees it and puts out a signal. I'd have to actually play with the particular design to find out exactly what is going on but the first thing is to verify exactly where the module will trip on the track. The thing that is really strange is that the engine approaching the end of the block trips the next signal and I can't really think of anything that would cause that unless the engine rolls onto a last part of the track which is electrically isolated from the rest and is fed power directly from the module and the DCC HF signal is feeding across the wires going up to the track.

-- Bob May

rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net

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Puckdropper 17 years ago

"Bob May" wrote in news:Z-Kdnd4APNGHVHbUnZ2dnUVZ snipped-for-privacy@o1.com:

It's time to do some snooping under the layout. I'm supposed to be documenting the layout electrical system anyway...

The two detectors are wired in parallel with other feeders (which now I know not to do), so perhaps when the locomotive gets close enough to draw most of its current through the detected circuit there's enough of a draw that the other detector sees it. Without actually measuring it, though, this is just a guess.

Thanks for all the help,

Puckdropper

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PV 17 years ago

I may have to give that a try someday. It's a nice circuit that I could easily think of other uses for. Thanks for the link.

The team digital ones go for $17-18 each depending on where you buy them. If sensitivity is an issue, there's a spot on the board where you can wire in a resistor to lower it. I haven't had to do that though. *

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