Dave Zucal posted:Adrian, in your video, the excursion voltage dropped quite a bit. From 15v to 4v. Would a second subway car totally knock it out? It would make one think that running a subway set or a string of passenger cars, on a small layout, that you would totally loose command control. But you don't. Also, many layout are built with MTH's RealTrax that have lighted Lock-On's and lighted switch tracks. It would be interesting to see a test connecting a few MTH track together with a few switch track and powered through a Lock-On. Then, take a measurement with the bulbs pulled out and see if the excursion voltage drops when the bulbs are put back in. If it does, it would be nice to see MTH get someone to start manufacturing (that style) replacement bulbs that are LED.
Generally I would say measuring the real DCS packets on a scope on the layout is definitely the best and gives you a detailed understanding of what's going on... not only amplitude, but overshoots, and general wave shape, all of which can be important. The telemetry train was like the middle tier and just gives amplitude readings of the DCS packet. The DCS packets are super short, like a few ms, and the line can stay idle for minutes if no one is pushing buttons. If you're alone and have to push buttons to generate signals on top of running the measurement it adds more complication to debugging. Sometimes the telemetry train's ADC, or even my scope will miss a packet if it's timed just wrong. That infrequency of DCS signal makes debugging hard, compared to the continuous waveform of the circuit here.
The idea of this is it continuously has the square wave on the track that's DCS-ish enough to be representative, but is continuously present so you can just tweak and tune with instant gratification on a display and not worry about how to send what command, and figuring out which one is train-bound and which one is TIU-bound. The scale is different, but you can quickly tell which passenger cars are, and are not, the major offenders.
One thing you could do is connect this circuit to a layout and see what happens to the voltage swing in order to detect non-helpful shunt impedances. You'd have to disconnect the TIUs first so their output impedance doesn't load the measurements.
