The good news is that a careful and conscious reading of the basis for the power and data modulation will definitively answer all these points for you without any more pedantry required. It’s common sense, and I think you have that sense.
There are a few thought-experiment ‘finger exercises’ you can do to make sure you have the peculiar genius of the idea captured – will it work if the rail-to-rail swings are sinusoidal instead of square wave; will it work if there is no digital modulation of the applied voltage; will it work if the square-wave voltage swing is less than ‘rail to rail’.
While we’re at it: calculate the required characteristics and state the likely characteristics of the keep-alive and device that detects a DC PWM signal from a power pack and generates a proportional DC output to a “DCC compatible” motor… just the thing that DCC doesn’t like… (There are likely multiple alternative ways; see which you think are best.)
What continues to surprise me is the lack of a quick link to one thread on this board that says everything in this thread, well everything understandable and relevant, but in one or two or even 100 posts.
I’ve searched for a simplified explanation of how DCC works without success.
I know just enough about computers and how they work to get by. What I don’t know or understand I can get. My brother holds a PhD in computing and is a professor of AI at Waikato University, and yes I’m even smarter than he is or so he says and he should know since he’s a teacher with a PhD and knows a genius or two. For myself, I’m not so sure. I don’t have a PhD nor a Masters. I have only a post graduate bachelors degree. I’m pretty smart but he seems smarter than that. And I’ve met even smarter people. You can tell if someone is smarter than you by the feeling you’re not fully understanding them. Mind you, there’s another much more common reason for that feeling and I get that frequently.
DCC isn’t analog so “scoping” gives you a misleading impression by displaying things that are just not there.
It is sometimes called a “square wave” which is an oxymoron. I’m a sailor and DCC is most definitely not a wave. An oscilloscope displays waves, or at least is intended for that purpose ( and yes I saw those tv shows also about scopes being used as computer displays and radar displays, etc etc, even read the books.)
As Locofi points out in their FAQ the DCC control signal is more like Morse Code but I say only if you consider that it also has variable length dots and dashes superimposed on the power flow. DCC isn’t AC because it isn’t analog. Polarity is also meaningless because it’s not analog.
I mean DC as used in model railroading is used as exceptionally low frequency AC in one sense. The current alternates with each application of the reversing switch. You may laugh but bli uses this
Me too. It is amazing how little the “Know-It-All-People” actually understand.
Steve-O already locked one thread today for pointless arguing, maybe this one will get locked too.
Going in circles…
That would mean the “Know-It-All-People” actually have gained real knowledge and understanding of a subject, and not just read about it on the internet and acted like experts. Not going to happen.
In Florida we like to say that a child that has dragged an alligator home by the tail understands a lot more about it than his friend who just read the story.
It is easy to pick out the people in here that have actually built layouts and done things from those that just read about it and act like experts.
One could be one of the most knowledgeable persons in the world or just come across that way but without a trace of humbleness that intelligence is hard to be admired
Why take one piece of cake and share the rest with others when you can take the whole thing is a few people’s logic I guess …[:|][%-)]
This reminds me of a guy who used to work at Lockheed - brilliant engineer, but he just didn’t get eddy currents. He actually filed for a patent on how to use the ‘new discovery’ and requested it receive secret access restriction…
Sine, sawtooth, square and other waves are called that because the mathematics to describe them is similar. You can think of a practical square wave as though it had the attack and decay ‘risetime’ equal to that of a much higher frequency sine wave but good clamping on peaks. So the effect is to switch quickly between two voltage levels.
In practice, not only can’t you switch potential ‘instantaneously’ but you can’t stop fast slew precisely at a clamped peak. There are fascinating little artifacts that ‘ring’ a little at the “finish” corners.
The point of using a square wave in DCC is to get around problems of spike and inductance noise on the power wires. The voltage transition is clean, and as large as the physical power supply is regulated to deliver, so it is easy to pick out (we call this high SNR, or more precisely CNR because DCC uses width modulation) and the transition stays ‘latched’ high at either extreme of swing for longer than the average of much random noise or transients.
Now this matter of bit coding needs a bit (I couldn’t resist) more thinking: you don’t want binary states ‘on’ and ‘off’ like computer explanations for kids, and you don’t want them ‘positive’ and ‘negative’ pulses or peaks on a zero-crossing waveform either. So you have two different clock-timed pulses, one twice as wide as the other, for the two states, which leaves many possibilities for recognizing things like guard intervals or signal multipath re
it seems that the AC-nish of a DCC signal is confusing the issue of polarity and a proper understanding. AC does not need to be sinusoidal.
i think the confusion is how can a current alternate (go in opposite directions) if the voltage simply goes from zero to some value and back to zero.
a current flows between two points, one of higher potential than the other. current doesn’t flow in an incomplete circuit, an unconnected wire (exception antenna at RF).
current flows between the two rails of a track when they are at different potentials. when rail A is positive and rail B is at ground, current flows from A to B. when rail A is at ground and rail B is positive, current flows from B to A.
in other words the current flows in one direction then the opposite direction, alternating, AC, and due to a polarity change.
Which is the product I started this thread about - the 8 pin compatible with DCC ready locos plug is wired backwards with regards to functions. It has the white and tyellow wires +, and the blue -. DCC specifications for the 8 pin connector have the blue wire as + and the white and yellow are -.
ANd the other huge goof so far - they do not have an app fo Apple IOS. Only Android phones.
Even better - the original wasn’t a question, it was merely my observation that the vendor got the wiring backwards for a product that is supposed to plug right in to a standard 8 pin DCC socket.
and they see no need to reverse standard NMRA wiring even though their decoders don’t come hardwired. They also provide a simple LED test that, in my opinion, shows up LocoFi’s supposed “FAQscuse” as, at best, lame.
CVP has been at this a LONG time - starting with CTC-16 in the 70’s. Railcommand was an expanded version that added headlight controls, right before DCC. They make DCC systems, and AirWire itself has been around a long time, one fo the first commercial direct radio control systems, very popular with garden railroads. The throttles are even compatible between their DCC system and AirWire.
Locofi claims their decision was deliberate with a sound engineering basis. After all, they are explicitly not building a DCC decoder and do not claim to be.
Agreed the iPhone version is needed but they know that and are working on it. iOS is way different to Android so you hsvevto do them separately. Way more Android out there than iOS and it is inherently easier to work with, thanks to Apple.
I know all the jokes about lawyers, only a couple are very clever. I have two favourites: one starts with a reformed drunk offering a lift to a clergyman … stop me if you’ve heard it…and the second involves a debate about the need of the Almighty to sue the devil … both of those are pretty clever imho. The one about the blond bombshell who gets handcuffed to one of those supposed rarities: a lawyer who made it to heaven is ok,I guess, as is the one about recorded billable hours and age attained at death…then the lab rat one…
The good start punchline is pretty lame, just btw. Reminds me of the lawyer joke my uncle shared with me (he was a statistician so you can imagine how inappropriate this joke was coming from him):
Name the similarity between a barrister and a rhinoceros …(I can think of several but only one is the punchline)
Because they are making a decoder and claim to be doing so.
Locofi runs a DC loco on a DC powered track. It does not decode a DCC signal to do so. It offers features that previously were DCC only. Rail pro seems to be going down that path also.
Good news is I seem to have figured out DCC. I now understand the painfully semantic point that the control signal delivers the power concurrently with the signal. Which of course is the Achilles Heel of DCC and what I was pointing out in the first place, or trying to. Kind of a duh moment in retrospect (as opposed to doh, so eloquently invented by Homer).
DCC seems like a combo of Morse Code and internet packet code.
Amusingly, trying to explain DCC can feel like trying to explain the Schrodinger’s Cat “thought experiment” and QM…when is a wave really a particle stuff. Very funny.