Love it...

Dear PQ,

That's a brilliant little unit, I love it.
(of course, the techie side of me says "you should be able to confirm the polarity and switching function of any dumb track-based wiring with a simple DMM, long before the DCC booster is even connected, let alone fired-up..." ).

Another jobby-box which would be a worthy addition to the "travelling troubleshooting toolkit"...
(if the LEDs had paired back-to-back elements, the same box could be used for analog DC wiring too... ).

Happy Modelling,
Aim to Improve,
Prof Klyzlr

with a simple DMM

Blinkenlights?

Dear PQ,

What, a model RRer's version of "Blinkenlights"?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Polarity Tester

Hi There.  I am having a tough time, changing wired connections, and I cannot get the points polarity correct.

Would you tell me the size of LED's  etc etc that I need to make my own polarity tester.

It would really help me with my layout.    Passed Driver

New version

I've revised this circuit since this post went up-- here's a better version:

I simplified the circuit by removing one resistor, then discovered* that some LEDs can bleed enough back current to light up a bit, so I added a pair of 1N415 diodes to prevent that. With these diodes, I have yet to meet an LED that won't work. I mostly use the Generic Jameco grab bag offerings. The only trick is figuring out which ends of the LEDs to hook together. The cathode (bar) is marked by a flat spot at the base of the housing. I've covered this in more depth in my basic circuit building series.

*Well, had it pointed out to me. I tend to use high end components in my projects.

pqe

I have a similar...

...unit I built for when I was working with DC (you know back in the Dark Ages!) See DIagram Below:-

I mounted it all in the case from an old ballpoint pen. The probe is the metal part from a lead for a multimeter screwed into the tip after the ink tube was removed and the LED is glued into the top of the pen. It was very useful for trouble shooting under layouts as it did not require 3 hands light a multimeter. I usually used it by clipping the lead to the common return and then probing. WHen you probe the LED is pointed towards you so you don't need to look away to read a multimeter.  I set it up so that if the probe was +ve with respect to the alligator clip the red Led would light if it was -ve the green would light, if it was yellow (sort of) you had AC. You can guesstimate the voltage by how bright the LED is.

You could mount the Pelsea's DCC version in a pen too just use a three leg Bicolour LED and 2 wandering leads. 

turnout position indicator

i use this circuit to indicate the turnout position based on the polarity of the frog.

i use 30g wirewrap wired soldered to the track and embedded in a slot in the foam and the LEDs embedded in the foam near the edge of the layout.

This is the one I made

This is the one I made for testing N-Trak setups. The only thing specific to N scale is the spacing of the brass strips on the bottom of the box. I added the Digitrax Loconet cable tester on top with some double-stick foam take, so everything is together in one neat package.

N-trak has since transitioned form Cinch-Jones plugs to PowerPoles for electrical connections between modules. I've got a converter cable for that purpose now. If I were starting over from scratch, I'd use those instead of the CJ plug

Here's mine

Mine is made for HO, it has four contacts on the back for placing across booster boundaries. If correct the top and bottom LEDs will be off and left and right on. If address 0 is selected and set to speed the LEDs should be the same colour, also useful to see if address 0 is on. Any bad contact missing power on one side etc. will cause the LEDs to light incorrectly. Putting contacts at one end across a frog and stock rail will indicate frog polarity by lighting the LED on that end if there is voltage between frog and stock rail. 

Basically it just has Bicolour LEDs (and resistors) between each contact.

Mike

Mike - article please!

I'll see what I can do.

I'll see what I can do.

test light

I just use a plain test light, like you use on cars. I have one I bought at Walmart that has a bicolor LED instead of a bulb.

Richard

Mike, it looks great! I like

Mike, it looks great! I like your idea and I drew something, which maybe is very close to yours. I used two Pelseas' circuits "crossed" and two indicators (led 3,4)  for the power in rails. I would like to build it on a bogie.
4 GREEN ALL OK
  

 

Tagged

Tagged for future reference.

Multi-Meter

Digial Multi-Meters are available very reasonable ($10?) at your local auto parts store. Set on 1-20v DC it will read polarity. Plus, you get all the other functions for your initial investment. (Continuity, ohms, etc, etc.) A Multi-Meter is what I used to determine my NCE's default polarity on track. Simple, simple, simple.

Andre

Andre the DCC is not DC, so

Andre the DCC is not DC, so no polarity in the sense of +/-

DCC has phase, not polarity

Vasilis..

I must have misunderstood the question/issue.

Andre

DCC phase/polarity

Joe, nice to see the more correct explanation that the DCC signal can be out of phase between blocks if the feeders are swapped.

I guess the polarity word usage is a holdover from DC as if the polarity in DC is reversed at a block gap you will get the engine stopping with a short, which is the same appearance when the DCC polarity is reversed.

So maybe more correctly we should be calling these circuits DCC phase detector, not polarity.

phase vs polarity

if the two wires are always out of phase, they have opposite polarity

Multimeter

The cheap multimeter comment is spot on though, with one minor tweak - use an AC scale, not a DC scale.  You should be able to measure voltage to the opposite rail on either side of the gap, but not to the same rail on the other side of the gap.

The DCC polarity checkers are just a slightly more convenient way to do that quickly.

Phase vs Polarity

The terms “phase” and “polarity” refer to two different things and should not be used interchangeably. Phase implies a shift in time relative to some reference while polarity is simply a reversal of positive and negative terminals, which DCC does not have a + and - terminal. Just because the signal is 180 degrees out of phase, which would be the case of swapping feeders does not make them opposite polarity.

.

while DCC may describe the terminals as A and B instead of + and -,  connecting the A side to the B side would be a polarity issue.   the A terminal always goes positive and the B terminal goes negative and visa versus.  The signal is not shifted.    The voltage at the B terminal is not a shifted version of the A terminal, it is the opposite (polarity).

if the output of two boosters were out of phase, you would measure a voltage between the A or B terminal of one booster and either the A or B terminal of the other booster because the signals on both booster are not 180 degree out of phase, maybe 160. 

Reasonable man interpretation...

I think it's reasonable, if not perhaps 100% technically correct, to use the word "polarity" in the context that if you connect two things of opposite polarity, something goes bzzt-pop, whereas if you connect things of the same polarity nothing bad happens.