Yet another "what were they thinking" from someone who wants to be a DCC alternative

[richhotrain]

York1

I wish I knew what you are talking about.

No you don't, and you don't want to. It is a whole lot more fun just "running trains", and not worrying about what makes them run. I just don't know why some guys just want to try to make model railroading tantamount to building a super computer.

Rich

[Bayfield Transfer Railway]

richhotrain

 York1

I wish I knew what you are talking about.

 

 

 

No you don't, and you don't want to. It is a whole lot more fun just "running trains", and not worrying about what makes them run. I just don't know why some guys just want to try to make model railroading tantamount to building a super computer.

 

Rich

 

 

I was on the Email list for the DCC standard before its adoption, with Stan Ames, Dick Lord, and others.

There were a large number of people who just seemed to want excess complication.

 

[Bayfield Transfer Railway]

A kitchen stove is extremely primitive technology if you spend under $500.

Yet nobody complains.

[rrinker]

Are you really that hung up on terms? No, you aren't "programming" the decoder in terms of writing a computer program. Neither is the DCC system, the decoder comes pre-programmed with firmware to respond to the DCC protocol, along with various user-controlled variables to adjust the behavior - hence why they are called Configuration Variables.

 As for your responses to the idea the DCC is just a protocol - I don;t undersstand what you are missing. DCC only specifies the packet format for the data transmission and the waveform used on the rail signal. When you get down to it, that's ALL it specifies. It does not specify how the user interface devices connect to the command station to tel lit what data to send, it does not specify anything about what the user interface devices look like. You've got everything from a handheld miniature lcomotive control stand (Proto Throttle) to touch screen smartphones to simple LCD display screen devices with knobs to very simple devices that just have a knob and some buttons, no screen whatsoever. Or even a full blown computer - running Windows, Mac OSX, or Linux. They connect via numerous wired formats, proprietary radio formats, and WiFi. 

 The NMRA controls and defines none of that. They only care about what comes out of the track connections, and how the decoder in the loco responds.  

 You still haven't explained 'primitive'. At the same time you praise truly primitive locos that didn't need instruction manuals (because they just basically had wires from the track pickups to the motor and no other features), you condem a modern loco as 'primitive' because it requires an instruction manual to exolain all those advanced features.

                              --Randy

 

[Bayfield Transfer Railway]

ULTRACREPIDARIANISM:  Expressing opinions outside of your knowledge.

 

[tstage]

[richhotrain]

tstage

 

An Internet troll is a member of an online social community who deliberately tries to disrupt, attack, offend or generally cause trouble within the community by posting certain comments, photos, videos, GIFs or some other form of online content.  

https://www.lifewire.com/types-of-internet-trolls-3485894#:~:text=An%20Internet%20troll%20is%20a%20member%20of%20an,all%20over%20the%20Internet%20%E2%80%94%20on%20message%20boards%2C

[Bayfield Transfer Railway]

"I don't understand what people are talking about, so I'm going to write a lot of words to cover up the fact."

[ATLANTIC CENTRAL]

Lastspikemike

Looks like there are a few innovators out there already. Railpro has the right idea. Backwards compatible. 

Once you separate the command signal from the track power DCC isn't very useful. Wifi or Bluetooth is the way to achieve that. Then the track power can go  back to just standard DC.

Make just a radio throttle control board to stick into DC only locomotives and a wifi or Bluetooth system can run anything on the same track.

Works for dead rail also.

As for recharging locomotive batteries in a dead rail system, that's protypical refuelling/servicing  time. For steam it would include re-watering time. Inductive charging is very feasible. You would not need to plug in any battery, just park the locomotive over a "refuelling" track.

Reading a bit more about DCC confirms my earlier posts to my satisfaction. I have no need to explain and certainly no need to justify my posts.

The original poster complained about having to reverse the polarity of led lighting. Most often you can do this simply by reversing the plug on the power feed to the bulb. I agree it is unfortunate that soldered wires would be inconvenient to change. But splicing in a reversible plug could be done at the same time and is s good feature to have anyway. Really this is a drawback to using led bulbs rather than a criticism of this new system.   

It would be interesting to know if this was just an error or required by some other factor.

Considering all this information I am glad I decided to build a double isolated multiple  block  DC only layout to begin with. I bought the MRC Tech 6 because for me it was an extra DC throttle with DCC capability added basically for free.  Once I added the hand held throttle it was no longer a free DCC but then I also acquired the ability to run up to 6 DCC locomotives at the same time. Since running three locomotives on my DC only layout taxes my current operating skills I see no need for more DCC capability as yet.

I don't see me investing in a more powerful DCC system making any sense for me, given my affection for all the used DC locomotives I have decided to acquire.

Change is in the wind and  Tech 6 ought to be enough for me for the foreseeable future.

 

 

I am a big believer that direct radio, like Railpro, would be a great system.

The problem with Railpro as it exists today, is the pictograph throttle.

I have over 130 locos, I'm not searching thru 130 pictures to assign a throttle to a loco.

It is easy to imagine the perfect throttle for your current needs in the hobby. it is yet another to imagine a throttle that will meet the needs of a large percentage of modelers who have different goals, different size loco fleets, different size layouts and desire different types of operation.

My Advanced Cab Control DC is tailored to my needs. It can be modified and adapted to a variety of needs. But it must be custom designed for each layout. And, it helps if the layout is designed with some of its basic parameters in mind.

Likewise, DCC is very suited to a wide range of different layout conditions and user goals.

Since you are so sure you know what would be better, let us know when you have this product ready for market........

Sheldon

[rrinker]

Lastspikemike

Reading a bit more about DCC confirms my earlier posts to my satisfaction. I have no need to explain and certainly no need to justify my posts.

 You certainly don't, but posting controversial statements with no explanation is classic internet troll behavior.

 Clearly you haven't read up that much on DCC, as your paragraphs after that explaining away my original post make perfectly clear. The product is a direct WiFi control system, not DCC, however they vendor made it with a standard NMRA 8 pin DCC decoder connector. Except they made the function wiring backwards. So while you can just plug it in, no soldering required - it won't work with LEDs. Drawback of LEDs? Well, if you want more primitive incandescent bulbs...  What's the point of having a plug and play install if you then have to solder and swap the wiring around? Might as well just make the receiver something that solders in.

 As for why - it has to be a mistake. Whether the output is active low or active high is a simple software issue for the microcontroller, and the drivers to get enough current, well, every DCC decoder uses one or another component that is commonly available. So there is no excuse. 

 As for fitting a reversible plug? Why woudl you make soemthing harder to use? In the case where there are a lot of lights in the shell, it's quite common when isntalling DCC to put a plug or plugs between the chassis and the lights, so you can remove the shell without leaving long excess length wires curled up inside the loco, just asking to get wrapped into the drive mechanism. You use polarized connectors, not reversible connectors, so you can plug things in and put the loco back together and be confident the lights will all work. Having a reversible connector just makes it more likely to make a mistake, and give zero benefit. DCC is always common positive. Ring RailPro receivers also use a common positive and come with an NMRA standard connector so they can just pluf in to a DCC ready loco. Only MTH and this WiFiTraxx module do it backwards, and MTH doesn't really matter because they don't sell their DCS decoders for separate installation. They are pre-wired into their locos, so it doesn't matter, unless you want to rip out their electronics and use standard DCC.

 As for the controllers, I'm with Sheldon, even though I use DCC and he doesn't. Scrolling through a list of pictures might seem 'cooler' to younger people, but it is far less practical than simply keying in the cab number of the loco you want to run usign numbers. It's technology for the sake of technology, so you can say "ok look, that 'primitive' DCC only has a 4x20 monochrome character LCD, outr system had a 4.7" full color high res display" Yes, and what exactly does it improve? It might be 'cool' and 'fun' some someone with a small layout and a small number of locos, but for anyone who has an actual fleet of locos and/or actually operates their layout, it just gets in the way. Is it really faster to scroll through 100 pictures of locos to get the one you want than to press a maximum of 6 buttons to select ANY loco directly? (the loco select button, up to 4 digits, and the enter key) Who does this make it easier for? Really little kids who can't read numbers yet, so they can scroll to a picture of Thomas and run it? We will occasiionally allow kids that small to run trains on the club layout, but they get handed a throttle that already has a train selected, and pretty much the only thing they do is blow the horn. Older kids may be instructed to watch the signals and may have to slow or stop the train, but those kids could also easily be taught how to select a different loco. 

 Change is always in the wind, DCC has not remained static for 25 years. Battery on board is still not really small enough for HO, except steam locos with tenders, and definitely not there for N scale. For HO diesles, it usually requires running a dummy permanently attached to hold the batteries. Not suitable for prototypical operation. At the opposite end of the spectrum, direct radio control and batteries has been used in G scale for many many years, it's nothing new. I'd almost think it foolish to build an outdoor layout and expect it to run on power conducted through the rails, DC or DCC. The biggest problem is that the systems that have electronics small enough to use in HO, even if they still draw power fromt he rails, is that there are multiple vendors entering this space, and none of the systems work with one another, they are all proprietary. This was the state of command control before DCC. You are at the mercy of one particular vendor. Without a standard, it's not going to take off in any sort of mass adoption. Command control was around 30 years before the NMRA DCC standards were established - some well-known layouts used one system or another, but it wasn't widely used. Companies came and went over those years, stranding people. 

 And one final thing. The whole idea of yours that combining the signal and drive power is 'primitive'. Combining them is what made DCC practical and successful, compared to all the others which superimposed a weak AC signal on a steady DC track powe, or something similar. Many of those older systems, the address of the loco was set by a hard wired jumper inside the loco. The receiver just counted pulses - if the jumpers were set to make one address 7, then it counted pulses and ignored the first 6 and responded to the 7th. After trying to pick those low amplitude pulses out from the noise and spikes placed on the rails by the brushed DC motors in the locos. DCC is fairly immune to that. 

                                    --Randy

 

[Bayfield Transfer Railway]

Lastspikemike

 

 

Bayfield Transfer Railway

A kitchen stove is extremely primitive technology if you spend under $500.

Yet nobody complains.

 

 

 

 

Not true. Even the simplest electric stove is not primitive. I mean you compare that to an open fire for cooking? Seriously? Can you even build a cooking fire ???

 

 

why yes, I can.  Eagle Scout and all.

 

and explain to me how a cheap electric stove is more sophisticated than DCC.

 

Please do.

[SeeYou190]

What is going on in here?

I don't use DCC, but I have operated layouts with DCC many times.

DCC seems wonderful for what it does. Simplified wiring, direct control of a locomotive, lights, sounds, and it was easy to learn.

It might be an old system now, but I don't hear too many people saying the system is not good enough. It seems to do everything that DCC users want it to do.

Promitive or not, that seems to say to me that it was designed right from the beginning.

My Samsung oven was about $500.00 when I bought it. I don't know if it is primitive or not, but it sure does a lot better than the 25 year old oven it replaced.

I can also build a fire good enough to cook hot dogs and s'mores. What else do you need?

I don't know what that has to do with anything.

-Kevin

[gregc]

Lastspikemike

I'm not advocating replacement of DCC. I point out that it is in fact a very primitive software system not readily accessible to current computer users with very little interest in "coding".

requests to clarify what a more modern improvement (not replacement) would be has been evasive

comparison of DCC to a TCS throttle compares the communication with the loco and the human interface

comparision of DCC to "dead rail" compares a wired approach to a wireless approach requires a "replacement" of the system.

it might be interesting to consider what the NMRA might propose today if DCC did not exist.

 

The NMRA baseline digital command control signal consists of a stream of transitions between two equal voltage levels that have opposite polarity

Lastspikemike

My understanding of DCC, limited as it is, is that the main power is not a true AC but it does differ from the control signal and that both sets of power are transmitted down the rails concurrently.

what does "both sets of power" mean?   there is no separate (e.g. high frequency) carrier for communication.

Lastspikemike

The decoder picks out the control signal and also converts the pseudo AC into DC (I guess "rectifies" is the term) with the variations in voltage required to control motor rpm.

"variations in voltage required to control motor rpm" suggests that the track voltage is varied to control the motor voltage.

Lastspikemike

The power is phased and the alternating aspect  is alternating the voltage in tiny amounts but not the polarity.

the polarity does change.   the polarity is modulated to communicate bits.    this approach is very clever because it requires a minimal of parts to modulate and demodulate.

 

i often find the best way to clarify my understanding is to state it and listen to the responses.    my goal is not to win the argument, such as a lawyer might in court, but to learn.   

 

 

[ATLANTIC CENTRAL]

Yawn..........

[gregc]

Lastspikemike

Direct wireless communication between the throttle unit and the decoder board is superior to DCC.

if that is what you suggest as less primitive, glad to hear it stated

Lastspikemike

I'm not able to understand the remark about the throttle (which actually generates the control signal) being the interface and somehow DCC being different.

glad to hear you say "not able to understand", suggesting a desire to understand

if by "throttle" you mean the device used by a user to control a loco, the DCC standard does not describe how it works or how it communciates.

multiple "throttles" ("cabs") communciate using a proprietary protocol to a single "command station"(which may control multiple boosters).  the command station controls the polarity of the track voltage and it is the timing between polarity changes (not frequency) that represents a bit (see below)

DCC is different from the control system.  NCE and Digitrax throttles are different but both support the same DCC protocol over the track

Lastspikemike

Dead rail locomotives can run on a DCC track

it certainly can since "dead rail" doesn't require track power

Lastspikemike

It seems direct wireless operation of a NMRA standard DCC decoder is already technically and economically feasible.

while you could transmitt DCC packets using other means of transmission, both wired and wireless, DCC specifically describes a wired transmission mechanism.   i don't doubt that some have built built wireless front-ends for DCC decoders albeit with additional hardware and demonstrated its feasibility.

i'll argue that wireless DCC is not DCC (e.g. DCC does not specify frequency or modulation method).

Lastspikemike

The control unit (throttle actually) adds a frequency modification transmitting the digital control instructions and, in some cases, communications back from the locomotive.

not frequency

one or more control units (throttles) communcate with a single "command station"  that sequentially generates DCC frames for each active loco decoder.   a booster receiving the frame data from the command station provides power to the track.

DCC communication represents bits by time between polarity changes.  each bit is represented by a pair of polarity changes completing a cycle where the polarity is both positive and negative for the same period of time.

 

most DCC systems do not support communciation from the decoder back the command station.  I do not know where the Bi-Directional Communciations Standards stands.

Lastspikemike

You clearly like to read into words meaning that isn't there and then construct an argument or discussion about something not said.

i am an EE and interpret words literally looking for a complete, correct and unambiguous statement and hope to do the same.

i am not looking to make a technical distinction to win an argument.  i do question an ambiguity when things are incomplete, incorrect or unclear.   i am trying to establish a clear understanding

Lastspikemike

The decoder varies the voltage and polarity of the power delivered down the rails in order to run and control that locomotive just like a standard DC controller does.

a "decoder" is in each and every locomotive.   it does not vary the power on the rails, it receives power from the rails and decodes DCC frames from it.    the decoder in the locomotive uses an h-bridge like circuit to provide power using pulse width modulation to the DC motor in the locomotive of either polarity.

Lastspikemike

All of this information is readily available over the internet,

yes indeed. i've provided references.

[rrinker]

 RailPro can't run a DCC loco, its receivers can use AC, DC, or DCC power in the tracks, it doesn't car which. That simply means their circuit has a rectifier on the track inputs.

 There actually is at least one dead rail system that uses the DCC protocol but over a wireless link. It's the one developed by Tam Valley and now sold by DRS. The transmitter side gets a standard DCC signal from an existing DCC system, and transmits it to a receiver in the loco with then drives a standard DCC decoder. Sound or not, you can use any decoder you like. The power source comes from an onboard battery pack. The obvious downside is that you need that much more hardware to fit inside the loco, and it's just not practical for many scales in common usage. Even with the best miniaturization available today, straight DCC is pretty tough in Z scale, let alone adding a radio receiver and batteries.

 DCC systems do have a common around which the track voltage does go positive and negative around. Relative to an external power supply, it may be generated as 2x the baseline, but there is a system common that references the center point, and most system include in their instructions the information that this common needs to be connected between all boosters. In fact, one way to measure track voltage recommended by Digitrax is to measure the DC voltage from Rail A to the common, and from Rail B and the common, and add them together. Still think the DCC signal is only a positive going waveform?

 One DCC booster can run your entire layout too, if the Tech 6 has enough power, so does one DCC booster. Not sure why you think otherwise. ANd common rail wiring stinks for DC too, I never used it even back when DC was the only way to control trains. I ALWAYS gapped both rails and ran TWO wires to power each block. But to say you can't use DCC with common rail is actually not true. It simply requires that each booster use optically isolated inputs so each booster is electrically isolated from every other one, yet still gets the same command signal.

 "Primitive software system not readily accessible to modern computer users not interested in programming"? If modern computer users are not interested in programming, then why would a system with an accessible programming API (hint, DCC has one, as do the major manufacturers' proprietary throttle interface systems. There are DIY DCC decoders, and even full systems. But the whole point is to NOT have to program anything - hence a wide variety of off the shelf devices for controlling, monitoring, and signalling) be any less primitive or more desireable?

 How is a simple electric stove not 'primitive'? It's a rheostat connected to a heating coil. That's a pretty primitive electrical circuit. The oven simply adds a thermostatic switch to the mix. My gas stove is even simpler, a gas valve and a burner. All the fancy electronics in the back, to give me a digital clock display - that's all for controlling the oven. All the electronics do is enable me to be lazy - I can walk away with something baking and the oven will shut off by itself at the proper time. 

 You've got more than one EE in this thread. Suffice to say I think we have a pretty good handle on just how a DCC booster and decoder actually work. If Greg's explanation doesn't clear up some of your misconceptions, I'm not sure what will.

 Instructions printed ont he back indicate complexity? MRC's claim to fame is that their system is so easy to use, the complete instructions are printed ont he back, instead of a multiple page user manual. It's a marketing white lie, as they leave out many things the system can do in those abbreviated instructions, but ANY system that allows control of multiple locos is by definiteion going to be more complex than a DC throttle with a speed knob and a direction switch. You aregue that DCC is primitive and then complex - which is it? - but then say a direct RF system is less primitive - but it will be just as if not more complex, because RF design is almost always more complex than a wired system. ANd you still have some of the same issues as with DCC, like addressing each loco so your handheld controls your loco and your buddy's handheld controls their loco. Therew will have to be a mechanism similar to DCC where you decide what address you are going to use, and the system sets that address in the receiver. ANd if the system instead uses an internal address it never exposes to the user, and instead uses pictures - we're back to that whole "what happens when I have dozens of locos" thing where it is completely impracticatl to scroll through pictures on a handheld LCD screen trying to find the one you want - compounded by having multiples of the same engien type. How do I tell which on my dozen RS3's I am selecting? By trying to read the road number (on a small handheld LCD screen, color and high resolution notwithstanding)? This is a horrible idea for a user interface.

                                   --Randy

 

[Track fiddler]

Wow!

You know, ... I don't find it hard at all to admit I don't understand some of the things in this thread.  Frankly that's why I shut up and listen.  I like to learn things whenever I can,  It keeps things interesting.  

My ex-wife was one of Those "No-It-All-People".  I tend to avoid Those like that anymore

I will say this though.  I do understand this has been one of the more entertaining and interesting threads I've read in the last 3 years

 

Thanks for posting

 

 

TF

[Overmod]

I think our self-characterized BS professional should look more carefully at why the DCC power is implemented as it is, and ought to be retained even if unmodulated.  It is NOT slightly higher voltage DC -- although it acts that way in the first step of 'decoder' operation -- and it is interesting to note that it provides a way to eliminate 'polarity' as an issue completely; no more fancy arrangements for reversing loops, frogs and the like.

 What is not as clear -- and this was a very significant concern in the 1990s, when things like V32.bis over POTS was important -- is that the structure of data communication explicitly zeroes out any direct-current charge transfer due to modulation concerns.  Some of the more complex constellations used for 'high speed' modems had to be very carefully laid out to avoid what was basically DC charge transfer over time in a way difficult to dissipate.  The inverted modulation scheme shows to me that key people were aware of the importance of this.  Brother Mornard, who was there during the standards process, may have some knowledge or recollection of this.

As a peripheral and not entirely pedantic point, sometimes solutions that did things that now appear 'primitive' in hindsight involved perhaps wildly more expensive and 'high-tech' approaches.  An example probably familiar to many is the evolution of high-speed dynamic random-access memory.  Some of the features in SAGE in the 1950s required enormous cost and complexity to do very simple things; the original patent for video-on-demand actually involved multiple cameras with little glass slides to render the 'on-screen prompts' as even ASCII character generation was not an evolved technology -- hard as that is to remember!

[rrinker]

 Indeed - on screen generated graphics even in the 80's in professional TV studios look so laughingly silly these days. Prettyy much any computer can do a far better job of superimposing text and other images on a video feed, but as late as the late 90's, the hardware to do this was not cheap. Now it's a device you can plug into a USB port. It was all the rage 15 or so years ago to make your own videos with the lightsaber effect from Star Wars - something that previously had required (originally) hand painting frame by frame and later a whole rank of computers to render (and not in real time), and now could be done in real time on any reasonably powerful home computer. Look at all the YouTube content creators using green screens these days - now in real time. With no fancy equipment, nothing at all like a full blown TV studio.

 Back to DCC - indeed, there are several reasons for making the DC average be 0 volts. Although in another (maybe not so brilliant, depending on your experience) option was to build in the concept of stretching one side of the 0 bit to introduce a deliberate DC offset to allow non-decoder locos to run. The usability varies depending on the type and quality of the motor involved, but it does work fairly well in at least some cases. Loosely built motors, like the old Athearn gold sided motors where even the magnets aren't glued in place buzz very badly which renders the utility of using zero stretching somewhat limited, but others can be fairly quiet with only a mild buzzing. Coreless motors of course are destroyed in short order due to no way to dissipate heat, but coreless motors were an issue with the earliest DCC decoders as well because they used low frequency PWM drives. With any 'modern' DCC decoder (which goes back quite a way - only the very earliest and then some super cheap brands used the low frequency drive), you can drive a coreless motor in perfect safety.

 I must confess to being around when the initial talks started to create a standard command control system, and as far as features go, it was CVP's Railcommand that did the most. The initial Lenz system was MUCH more limited than what became DCC - perhaps more proof that DCC is not 'primitive' - the original basic design allowed for much extension with little change, to get a wide variety of features, which has continued to be extended. I believe the original only had 2 functions, but by the time it was submitted for approval, there were 8. Then this was expanded to 12, and then 29. Originally there were only 14 speed steps, but this was expanded to 28 and 128. Railcomm has been added for 2 way communications - this was originally Lenz proproetary but is now been standardized by the NMRA. DCC is a growing standard that has evolved over the years, it is not the same today as it was in 1995.

                                          --Randy

[Bayfield Transfer Railway]

The NMRA DCC Standards are available online.

 

I recommend starting thete.

[Overmod]

Lastspikemike

Some say DCC is like AC and some say not. Some say polarity exists in DCC and even that polarity is significant while some say not. Some even suggest that the power and the control signal are "the same thing' and some say they are separate "things".

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.)

[richhotrain]

Lastspikemike

I've certainly learned a lot about DCC I'd looked for before and could not find.

Certainly clear to me now why there's not even agreement in the online information that is available.

Some say DCC is like AC and some say not.

Some say polarity exists in DCC and even that polarity is significant while some say not.

Some even suggest that the power and the control signal are "the same thing' and some say they are separate "things".

What for me at least is new information about DCC is very useful to know even though I am still processing a lot of the detail.

I certainly understand semantics and pedantics if anyone was still wondering,

 

Why not just buy a DCC command station and scope it? Find out for yourself what goes on with the DCC signal.

 

[SeeYou190]

ATLANTIC CENTRAL

Yawn..........

Yeah... me too.

Track fiddler

one of Those "No-It-All-People".  I tend to avoid Those like that anymore

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....

richhotrain

Why not just buy a DCC command station and scope it? Find out for yourself what goes on with the DCC signal.

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.

-Kevin

[Track fiddler]

  I hear you Kevin

yep yep yep

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 ...

 

 

TF

[Overmod]

Lastspikemike

It is sometimes called a "square wave" which is an oxymoron. I'm a sailor and DCC is most definitely  not a wave.

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 recovery.  
Remember the bakancing of charge?  This is why you send the 'inverse' of a control sequence: any tendency for electrons to drift where they are hard to cope with is inherently balanced in no more than a few cycles.

If you wanted to do this with a sine wave or modulated signal, you could do it by specifying a voltage transition well down from peak -- like clipping in an audio amplifier.  Some timing precision is compromised and of course the information in the clipped part of the wave is lost -- you will now recall that DCC uses the full rail-to-rail voltage difference to modulate its signal; it can in essence be no clearer.

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.)

And if your 'scope was not made by the company that built Chevy Chase's discount phones,  you will find a square-wave setting among its controls.  Note that logic probes do essentially the same signal and timing recognition but they resolve in ns. or other timing and not a continuous display of SHM.

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.

This is a reasonable analogy if you know both how the power modulation and Morse code groups work. Technically a bug could be used to send bistate binary in 'dashes' and 'dots' with the same meaning the convention in DCC uses.  But the purpose of dashes and dots in practical Morse as used for all but special communication is to form recognizable tone patterns to the ear, not convey 'letters' sequentially over the wire to a printing device as in Morse' original... and not very workable... patent.

DCC isn't AC because it isn't analog.

But of course the power part of DCC is analog, and the production of the digital waveform is also analog.  Only the supervised information is digital.

Polarity is also meaningless because it's not analog.

It is never anything but analog, an indication of potential differences measured by physical equipment.  Ordinary DC works (in great oversimplification) by shoving electrons in one direction, and because of how attached devices use that electron flow whether it is pulse-modulated or not, we consider the polarity of DC flow significant.  In this connection the 'double voltage' rail-to-rail in the DCC supply can be thought of as two counter-polarity interrupted DC flows, alternating across the zero crossings; either of these could be 'half-wave rectified' and smoothed into a DC current if desired polarity -- in fact, both can be.  A good decoder in fact will 'know' which of these half-flows to use on any given locomotive facing in any direction... which is a big reason 'polarity' issues are so little a concern in evolved DCC.

Note that a simplistic understanding of sinusoidal AC charge can be considered just this way with some of the circuits the EEs have been describing; one reason RMS measurement is used is that it gives average for a smoothed rectified waveform and not the actual high-voltage peak in sine-wave AC.  

[SeeYou190]

Going around in circles.

We are so far from the original question that we might need to engage the hyper-drive to get back on course.

-Kevin

[gregc]

Lastspikemike

DCC isn't AC because it isn't analog.

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.

Lastspikemike

The power is delivered by digital wave that alternates between zero and max voltage on each rail and each rail has to be out of phase with the other rail.

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.

The NMRA baseline digital command control signal consists of a stream of transitions between two equal voltage levels that have opposite polarity

Lastspikemike

The DCC control signal is not communicated by polarity changes.

the spec clearly says it is and I previously showed how the time between polarity changes encodes bits of information.   (see link)

 

Lastspikemike

Why use a picture when 10,000 words would do?

are you serious?  or a waste of time?

 

3318 101700

[tstage]

This song from the 70s might sum it up, as well:

[tstage]

Lastspikemike

??? I'm a litigation lawyer. Why use a picture when 10,000 words would do?

Well, you know what they call 500 lawyers at the bottom of the ocean?

A good start...

[richhotrain]

tstage

 

Lastspikemike

??? I'm a litigation lawyer. Why use a picture when 10,000 words would do? 

Well, you know what they call 500 lawyers at the bottom of the ocean?

Lastspikemike

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

With a post graduate bachelor's degree no less.