What’s the best (well, easy and cheap) way to test DCC at the rails, besides a loco? I know DCC basically square-wave DC, but can I use something as simple as a multimeter to see if rails are live?
It depends on what you want to accomplish.
If this is a dcc system, and you just want to know power is on, any voltmeter on AC will be fine.
If you want to know what the track voltage is exactly, then you need a “true rms” voltmeter
If you are trying to see if you have a good signal, then a cheap accessory decoder with a light and you command the light on and off would be a quick and dirty way to know that you have a reasonable DCC signal.
Greg
There are other tools that I use, but of course they cost more.
I’m looking for a packet analyzer that is inexpensive that uses a pc for the “brains” and minimal external hardware.
I’m spoiled because I have a portable packet analyzer, and that has really helped in situations where there appeared to be signal, but nothing worked (I had a messed up piece of equipment putting garbage on the rails)
If you find one of these used, buy it:
captures dcc commands, show issues with the signal, bad bits, errors in packets, shows packet timing.
Even with the very tolerant DCC spec, there’s still stuff out there that is marginal in sending and receiving commands.
https://elmassian.com/index.php?option=com_content&view=article&id=546&Itemid=663
ahhh… I remember now, NCE makes one too… (haha I guess I forgot I bought one)
https://sites.google.com/site/markgurries/home/technical-discussions/tools/dcc-packet-analysers
By the way, Mark Gurries is pretty much the top DCC guru around.
Greg
Thanks Dan, looks like a nice way to go, since the components are inexpensive, and most people have a laptop, although in the sunlight I’d prefer to have a mono LCD for readability.
Greg
Thanks guys, good stuff to ponder. I might even have enough parts in my parts box to build the circuit for the 'duino. Im not sure I have the 6n137, but I may have something close.
Right now I’m at the “Is this section really connected all the way back to the power?” stage. Simple continuity testing shows I’m good, but, well, I know how that goes. If that goes well, then Ill see about actually analyzing the signal itself.
Thanks again.
You could build a little tester with a bridge rectifier and a lightbulb.
Eric, that would at least tell you if there is power, but it won’t say much about signal clarity.
I have the parts to build a shorted track detector for when the clubs set up, I just haven’t assembled the parts yet. I really need to, so I can set the thing, clearly labeled “STD”, on the track and see what kind of responses I get.
If you have a wireless remote, then a simple FL4 from TCS with a LED or 2 and you can clip it to the tracks with a couple alligator clips and blink the LED.
Ahh, there is a FL2 for $23 list…
Of course if you email me your address I’ll send you an MRC AD322 decoder with a speaker for the cost of the USPS flat rate box.
Then you can check the horn command, which is one of the trickiest to get right.
https://elmassian.com/index.php?option=com_content&view=article&id=303&Itemid=336
Greg
You only need a diode bridge to test using an LED. I have a light bulb attached to my track outdoors and it lights up on DC and DCC to show me at least power is there. And it acts as a drain on the old Aristo 27mhz remote units I still use…
Yeah, the $5 voltmeter from harbor freight was one option. But a really cheap old decoder would prove the “DCC connectivity”, one way to interpret the topic.
If you had a dcc / dc layout, you could use 2 diodes with dropping resistors across the track, in different directions. One LED lit, DC, and a polarity indication. Both LEDs lit (possibly somewhat dimmer), AC / DCC
Or use CL2s, then the LEDs would light up the same brightness.
One if by DC, 2 if by DCC.
The electrons are coming, the electrons are coming!!
Following up with this. Greg sent me a couple MRC decoders, and today I set up my DCC command station through the node to the four blocks around Williamsport. Using some alligator clips I tested each block and got response on all four blocks. The detectors also triggered when I out a resistor across the rails. So, all good.
Just a reminder to those reading the forum, the horn on and off is one of the best tests, the nature of the command makes it the most “sensitive”…
Hey Bob, what did you think of the “engine sound”? Pretty pathetic huh? The first time I lit one of those off, I thought the gearbox on the loco had grenaded!
Regards, Greg
The sound is…interesting. The quality is weird, and it’s not QUITE monophonic. I can get then occasiona sound to overlap, but it’s not consistent. At least I can hear the horn from 20 feet away.
Yep, I knew there was a reason I had them… I knew they would be useful somehow.
If anyone else wants to do what Bob is using them for, email me (not private messaging)… Greg
Greg Elmassian said:
Just a reminder to those reading the forum, the horn on and off is one of the best tests, the nature of the command makes it the most “sensitive”…
That explains a lot. I have trouble sounding the horn/whistle on the club set ups sometimes.