Wonderful idea, possible enhancement

This is brilliant.  If it has been proposed before, I haven't seen it.

Here is a thought:

Build a more sophisticated version that can identify areas of dirty track in need of cleaning.

1.  Put an Arduinio on the flat car and equip it to read the voltage across the rails using its internal analog to digital converter.  Since dirty track will show up as increased resistance between the rail and a metal wheel, have the voltage monitoring circuit set up to draw something like 50 ma, to approximate the load presented by a DCC decoder.  If you measure the voltage with a typical very high impedance voltmeter arrangement, drawing very little current, it will be much harder to resolve the voltage drops that are due to dirty track.  Also, have the circuit measure the peak to peak voltage for DCC.

2, Push the car around the layout with a locomotive.  When the car detects DCC peak to peak voltage less than a threshold amount, have it sound an alarm- it has found a section of dirty track.

3. A more advanced version could count wheel rotations and use this to keep track of current position relative to some known starting point.  The Arduino could store a log of voltage readings as it traverses a route.  When done, you could export a table of data that could be displayed as a graph on a computer screen that shows the track voltage versus position.  You could apply thresholds to the data to classify regions of track as "very clean", "deteriorating" and "needs attention now."  A great task for a regularly scheduled MOW train.

If there is interest in this, and if no one points out reasons why this is a ridiculous approach (which it might be, I haven't finished my morning coffee yet), we could start a separate thread to flesh out the design.

Dennis

References

Dear Dennis,

FWIW, some "prior art" discussions which might be worth a look-over...

https://forum.mrhmag.com/post/sma24-%E2%80%93-working-scale-dynamometer-car-recording-drawbar-pull-track-voltage-speed-distance-more-12203477

https://forum.mrhmag.com/post/design-challenge-track-tester-for-dcc-12204330

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Seems to me any

Seems to me any sound-equipped loco without a keep-alive would do the job just as well... 

< < wicked grin

Seriously though,,    An LED will respond faster to short dropouts than an incandescent bulb. Use a 2 lead bicolor LED with a 1000 Ohm resistor and you get a DCC "polarity" indicator, too.

I have a lighted passenger

I have a lighted passenger train...  Including a few lighted Cabooses that do the same thing...

@ Prof Klyzir

As you have often said "the search box is your friend."  Case closed

Dennis

negative testing

As I said in one of the other threads (not sure it was one of the linked ones), what I think would be most desirable is a car that beeped or chirped when it lost power. 

You might not see a really fast flicker, in particular if you weren't looking right at the test car like a cat watching a mouse hole. And speaking of holes, a lighted car isn't much use for testing track in a tunnel (though if the track is already covered, how are you gonna fix it anyway?) 

With a circuit that used a battery or capacitor that would chirp when it lost power, you could sit back, relax, close your eyes, and wait while the car is pushed/pulled at a crawl around the entire layout. No chirps, no problems!

I'm not an EE so I can't design the circuit, and don't know how hard something like that would be. I'm sort of expecting it to be doable with a couple diodes or something. If it's a lot harder than I think, then forgetaboutit.

Of course....

... if the turnout had droppers in the first place and not relied on rail joiners the problem wouldn't have occurred.

I wire every piece of rail no matter how small. no voltage drops ever!

which rail?

i did the same, but have considered having 4 individual wheels and 4 leds to identify which specific rail/wheel is not making contact.     i've seen intermittent conductivity but the LED comes on when i press harder.   this assumes the contact to the wheel is reliable

if you have an LED between two front truck wheels and another between the right front truck and left rear truck you can identify which rail under the front truck has a problem.   if only the the led across the front truck wheels goes out, it must be the left front truck wheel.   if both leds go out, it's more likely the right front truck wheel/rails.

of course having contacts on the same wheel identifies the track segment under the wheel and not a segment the length of the two trucks

Another Approach To The Electrical Test Car

I used an old Stewart dummy chassis to provide the electrical pickup for my test car.  The green leds indicate power.  The red leds light if there is a phase error when crossing power districts.  Phase error detection is important when setting up large modular layouts.

Weight and schematic

Dear Jim F,

That looks like a great application, and the extra weight of the ex-loco frame certainly would help with "test pickup reliability"...

Any chance of a schematic for the unit?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS if there's enough power (Volts x Amps) to light LEDs,
there should also be enough to power a small simple piezo buzzer in parallel with each "LED indicator",
select audibly "tuned" buzzers, and Dennis's "audible feedback" suggestion could be do-able?