DCC - Alternating current?

TazzyTazzy

Gregc The debate if it’s AC/DC is long-standing. In short, some say it’s DC due to a lack of sinusoidal wave. Which is what my thinking was. However, the current is alternating thus, making it AC. NMRA has said that “The DCC signal is an alternating DC waveform”.

NMRA documentation muddies everything up and has referenced it in different ways. LENS has also called the signal Pulse Width Modulation (PWM), but it’s not, it’s Frequency Shift Keying (FSK). The signal doesn’t modulate as the duty cycle never varies. I think they called it PWM to increase their patent scope.

Additionally, there’s the entire ‘zero stretching’. Would this be DC then when it’s in use? Short answer: no - you still have the commands perhaps it’s just considered a DC offset? This is above my pay grade. Perhaps I need correcting here too.

Could you start with a new article that debates both sides of the argument? At the end of the article, you can link to the DCC Power article to learn more about encoding/decoding, etc. From the DCC Power article, you could link to your new article.

Now that I’m thinking, this might be a great place to start and it would help us (mostly me) provide direction throughout the rest of the DCCWiki. Additionally, there are little blurbs of this argument spread throughout the wiki. This would be a great time to consolidate and point to a new article that explains just this point. Not saying to go through the entire DCCWiki to look for these blurbs, just then whenever one is found, we can start pointing to this.

Perhaps you can take components from this article: https://dccwiki.com/DCC_Tutorial_(Power)
and start a new one? Would this be something you would be interested in? This will help you learn the wiki formatting, and get your feet wet (soaked?).

As a quick search, i found this thread interesting: https://ogrforum.ogaugerr.com/topic/is-dcc-high-frequency-ac-or-alternating-dc-based - specifically, a post by Chuck K.

Gregc

TazzyTazzy Feel free to tackle the DCC Bus Signals page and re-write it. It’s a wiki, go for it.

ok, thanks. sounds like a good place to start.

TazzyTazzy NMRA has said that “The DCC signal is an alternating DC waveform”.

as an EE, i’ve never heard the term “alternating DC waveform”, I think confusion is perpetuated by attempts to use “techy” terms. the vast majority of digital communication methods are AC (or should i say not DC).

the Bell Labs Writers Course emphasised explaining things rather that using technical terms that require further explanation, much less acronyms. I think avoiding the use of technical terms, especially the mis-use or inappropriate invention of new terms (e.g. “alternating DC”) would be a good policy in describing model RR electronics in particular because most model RRers are not technical, much less electronics savvy.

i hope my thoughts are consistent with what you have in mind

TazzyTazzy

Hey @Gregc . Was wondering if you’d be up for tackling creating a new article. For example, there’s a blurb on Voltage Drop article that touches on DCC being neither DC or AC. Would be great to point to an article that discusses why it’s neither DC or AC in the way we typically think AC is (sine wave).

Give it a go. It doesn’t have to be perfect, it doesn’t have to be complete, just put down your thoughts. Save it. Maybe in a few days, you’ll think of something else to add or maybe we will.

Gregc

thank you for suggesting how i could contribute.

DCC is clearly AC because the current changes direction. there is no in between. It’s irrelevant that it’s not sinusoidal. Almost all digital transmission between devices is AC (e.g. RS-232, ethernet, RS-485). this could be added to the DCC Signal page.

as for the Voltage Drop page i think it would be better if it concisely summarized the rather comprehensive TN-9.

TazzyTazzy

I’ve been on a writing streak the last couple of days. I made a first pass at it. It’s probably wrong, just go ahead and edit it to make it correct. Or expand on the discussion, provide references, add terms, etc etc.
https://dccwiki.com/DCC_Waveform

TazzyTazzy

Hrrm. Maybe this is a bad page title? It might be confused for DCC Signals. Whats a better name?

Gregc

i’m sorry, but i don’t believe many of the statements on that page are factual, i don’t understand the need to address the issue and don’t understand how it helps a modeler reading the page. all DCCWiki pages will have little credibility if they provide provide inaccurate information

there is no such term as “alternating DC” nor “bipolar DC”. DCC is a bipolar signal because it has 2 states and each is opposite in polarity

DCC does not use FSK modulation. it does not transmit a bit of information as a “symbol” represented by a frequency for some symbol period (the baud rate), many cycles at that frequency

it’s not really PWM because in PWM the bit value is represented by the duty-cycle of the pulse, the period it is on versus off. but in DCC the duty-cycle would always be 50% because both the period it is on and off are the same

zero stretching doesn’t provide a “DC offset to the signal” it makes the average DC level of the waveform non-zero so that a DC motor will be driven in one direction more of the time than not

i think i can help you by providing a technical review of DCCWiki page content, such as above. but if after some discussion you disagree with that assessment, i doubt i can contribute

TazzyTazzy

Gregc I wanted to get started. I’m not an electrical engineer. I even mentioned in my save notes from that page that it was probably all wrong.

Edit the page, and delete all the content if you think it’s wrong. Feel free to re-write it entirely. I mostly wanted to help you get started with wiki syntax & structure.

The same goes for other articles you find. Just edit the page. There’s no need for discussion, you are free to edit anything you see wrong. I appreciate you going through any pages and editing them.

To answer the nagging question people have: “What is my information is wrong?” Thats may or not be true, but someone else can come along and fix it. It’s even better if your can provide references to where information came from. See: https://dccwiki.com/Help:Reftags In the reference tags <ref>…</ref>, just put the URL where the information came from. Or a book & page number.

To answer your question of how articles like this help a model railroader:
Many people like to understand the electronics behind things, even if they cannot do anything to fix it or change it. This is the entire reason I get into railroads. I’ve zero interest in reailistic trains, to scale, weathering, signaling, etc. I got into trains purely because I thought DCC was awesome how it works.

Second, in this case, it can help explain why people need reverse sections.

I’m curious to read on the wiki what you put for FSK vs PWM and what the DCC signal is considered. 🤓

Cheers.

Gregc

what is the difference between waveform and signal? why have a DCC Waveform page and a DCC Signal page and a DCC Power page?

i think the only reason a model needs to understand if DCC is AC/DC is to set a multimeter correctly (to AC) to measure DCC track voltage. So simply saying
DCC is AC.
is complete, possibly on a page under wiring where measuring track voltage is discussed

  _I’m curious to read on the wiki what you put for FSK vs PWM and what the DCC signal is considered_

this is the problem for me, i don’t want to “correct” this, it should be removed. i don’t want to mention/correct invalid terms like “alternating DC” or “bipolar DC”. there are no such things

Gregc

so now there is a new page mentioning how DCC is not exactly AC among other pages (see [search](Under ABS or ABP, authorization is by written warrant - less efficient and time consuming and less safe.))

i had hoped to prevent inaccurate information from being posted to begin with, rather than rely on it subsequently being edited/corrected. information should be complete, correct and unambiguous. discussing it before hand rather than simple editing it provides a way to better understand perhaps what is intended to be said and to help describe it better