I do understand the OPs desire to educate, but as others have said, that does not permit misleading statements. Problems measuring the DCC supply comes up regularly as it is and saying it is DC will lead to people grabbing a multimeter, setting it to DC and then getting completely confused. Setting it to AC will at least get a reading, even if it isn't accurate. By all means make it clear that it is nothing like the mains AC, but please don't call it DC. Incidentally, in the UK we tend to call what comes out of the wall 'the mains'. Referring to it as [the] AC seems to be an American trait.
OK guys, lotsa points made here. While I was composing my overly detailed engineering response y'all blew right by me! Let me just make a few points: 1) The DCC waveform at the track periodically reverses polarity at a rate dependent on the applied data. As such it is a modulated AC waveform. To claim otherwise only creates confusion (and this includes the "alternating DC" (huh?) and bi-polar descriptions). 2) From a standpoint of how power and data are simultaneously carried via DCC, it is more instructive to think of it as a form of AC rather than a form of DC, as DC cannot be modulated or rectified, both necessary for the decoder to operate. 3) Rather than describing DCC as data applied to a power feed (which would describe a carrier current system such as X-10), it is better to describe the DCC track signal as power applied to a data signal, or data on steroids. 4) A decoder is not a "DC transformer" (no such thing), but can be thought of as a miniature power pack in the loco (with pulse power, even). And finally: 5) The Morse code and SOS example is like trying to fit the glass slipper on the sisty ugler. DCC modulation (essentially pulse width modulation or FSK of a periodic waveform) is not at all like Morse code, which is definately not periodic. Morse is a code (it is not a waveform) with four symbols: a “dit” which is on for one unit of time, a “dah” (not a dash) which is on for 3 units of time, a one unit space separating elements, and a 3 unit space separating letters. A top Morse operator (not me) can send and receive at 150 characters per minute. DCC sends at over 46,000 characters (bytes) per minute. Speedy, huh (Di-di-dah-dah-di-dit). DCC can be intimidating to newbies, and "DCC Simplified" is a great idea, but as posted (and based on the number of pages in this thread) it doesn't come anywhere close to achieving that lofty objective. When I get questions on the basics of DCC, I do my best to give an overview, but often turn to existing tutorials that provide excellent descriptions. There have been a number published over the years, but two of the best (IMO) are the following: http://www.loystoys.com/info/how-dcc-works.html http://www.siliconvalleylines.com/dcc/2009/Basics.pdf Sometimes it's hard to improve on a good wheel. Doug Stuard BSEE Amateur Extra (KM4FI) - 47 years MRR (AC, DC and DCC) - 57 years (on and off)
The following is from the Digitrax web site http://www.digitrax.com/appnote_basic%20troubleshooting.php Track voltage (output from the booster to the rail)is measured as follows: With the system on and with Track Status on, select the analog address,00, and set to speed 00. With a multimeter set to the 20 volt DC scale measure from Rail A to ground (the toggle switches on the booster are grounded), then from Rail B to ground. With the Scale switch set to N scale the readings should be about 6.2 volts DC, for each rail. Total track voltage is the sum of the two, or about 12.4 volts DC. At the HO setting the rail voltage should be 7.5 volts DC each. At the G/O setting it should be 10 volts DC each. The difference between the rail voltages should not exceed 0.2 volts. Satisfactory operation will still occur if the difference is as much as 0.5 volts I would think that the values mentioned for Digitrax would be very much the same for other brands. The ground (earth) location may be different between the brands. Gary
I feel your pain, Rick. We really took this discussion down a rabbit hole it didn't need to go down. And that's part of the problem with DCC. As you so clearly bring up, there's TOO MUCH of the wrong kind of information, and NOT ENOUGH of the stuff the user really needs. I wish I were in a better position to fix that, but I'm not, yet. As for DCC, it is not, nor will it ever be SIMPLE. But it really can and should be EASY. A lot easier than it is. In the other thread I used the example of computer tech in the 80's versus now. Things were a lot SIMPLER back then, but they were much, much harder to use. Unfortunately, making it EASIER while retaining the features we want means making it more COMPLEX. Sorry about the emphasis... just intentionally trying to highlight some opposites. I really think if we could just "nuke" the last four pages of this thread, and start over with inobu's original post (with a slight tweak to his otherwise excellent explanation of the track signal), we could have a great and very helpful thread. I hope it's not to late to re-rail it and get this train running. I've been thinking about the problem with CV's, but unfortunately haven't had any time to work out a solution. What we need is for somebody to tackle the rather tedious task of compiling and "humanizing" the CV descriptions, categorizing them in ways that make sense to USERS and not the designers who built the darn things.
The Digitrax procedure described is a good one for determining the DCC voltage by measuring each side of the waveform with respect to system common. Note that the signal on each rail never actually goes negative with respect to system common, but alternates between 0 and +V, with the other rail a mirror image. Looking at it from the point of view of either of the rails, the other rail is either at a higher voltage (+), or at a lower voltage (-), so a loco would see a +/- AC waveform. For determining proper voltages out on the layout (where system common is not usually available), the workable (although not entirely accurate) procedure would be a multimeter set to measure AC volts. The percentage error between the square wave DCC signal and the sine wave based calibration of the meter is pretty much constant.
It is funny how no one took the time to do what I did yet every one has made it a point to comment in a manner that detracts from the intent. It is a pity as I stated before this hobby in this country is falling behind and it has a lot to do with the mentality. Look at what Viessman and ECos is doing Europe while we are content with status quo. http://www.youtube.com/v/E011TNviyaQ&hl=en_US&fs=1& It takes broader thinking and reasoning to garner innovation and growth and I don't see it and can understand why. I started this hobby a few years ago and brought a few things to the table I was surprised at the things I saw but much of what I see is expected, now I will remove this video soon in that things have come to a disappointment but the time seems fitting. Spent some time and effort but I enjoy what I have. No, stop action its all one video stream. http://www.youtube.com/v/E-FESXZhmbo&hl=en_US&fs=1& Inobu
Look, I'm an Electrical engineer as well. And I appreciate the need to keep things simple, but there is a difference between keeping things simple and being wrong and/or Ignorant. The power on the track with DCC is absolutely, positively without question AC. It fits the definition of a periodic alternating signal. When you call it DC, you aren't keeping it simple, you are being ignorant and/or Lying. In point of fact, an inverter is only 1 way to create an AC signal (and there are Square and step wave inverters just to make life more difficult). Electronics have other methods. A DCC decoder, after processing the signal message takes the AC current being applied to the line, rectifies it and sets Voltage such that the DC motor will turn. It is in fact very much like a modern DC diesel electric which uses an inverter to create AC which is then passed through a rectifier to produce DC for the traction motor. The problem here is that you think of the DCC signal as a power signal, same as in a Block DC system. But power isn't what defines the signal. the decoder generates the power and that power is DC, but it rectifies it from AC. Below is a bunch of rambling: read at your own risk. I think a better way to think of DCC is that it is like a Compact Disc player. Both of them utilize Pulse code modulation. A compact disc is like a record. it has pits and groves that are read out. Those pits and grooves are turned into an AC signal on the line That AC signal then goes to a decoder which turns it into Analog power to drive speakers (and go through amplifiers and so forth.) Well, on the other hand, that's not so simple, because most people don't actually have Digital out CD players. Perhaps you have a Dolby Digital sound system. Your DVD player has a DD out which is a single cable yes? It plugs into your receiver which then turns that 1 signal into your 5.1+ speakers? DCC is the same. the track is like that cable. the Cab/controller is the DVD and player and the DCC decoder is like your receiver.
You need to know that you guys are all good with me. I realize each of you electronic's wizzards are tripping over each other in an attempt to communicate the right information and definitions. Perhaps, I shouldn't make fun of such efforts but you left the door wide open. This was supposed to be a thread about Simple DCC, not the complexities. Inobu, got us off on the right foot but Wow! What are we thinking? I don't need to pester you guys. I've got a thread where I posed a question that is now in run away mode...got to get back to it. cute:
He got us off on the right foot, but then immediately tripped over a stone on the path. If you deleted his comment that it is not AC, his post would not loose any meaning and would have the advantage of being correct. Now, if you want to call it PDC or pulse DC, then I might agree, but that's not keeping it simple.
Only problem is in an attempt to make things simple, he was fundamentally wrong on a number of counts (and at odds with most every other tutorial out there, which can only perpetuate confusion). What may seem correct on the surface and thus easier for a newbie to grasp, will only cause more confusion down the road as the newbie gains experience and finds out that his initial impressions don't match up to his new found understanding. Initial impressions should not be rendered obsolete by new knowledge. Get it right from the outset (and K.I.S.S.), add complexity later.
Quote from YoHo ".....you aren't keeping it simple, you are being ignorant and/or Lying." Based on the knowledge you profess, give us the reason that you did not offer your knowledge to those who need it, yet you are able to take time out to profess my ignorance so eloquently. Even you ramble from a CD player to Dolby sound.... having problems describing it? LOL This is the future.... LOL Inobu Go look on NMRA web site and you will see that they call it an alternating DC waveform. shhhh, we don't want the rocket scientist attacking them. shhhhh!!
Send a Private Message This is just a suggestion. When we see something that is an obvious error can't we send a Private Message to alert the OP and allow him to correct it? Just a thought!rolleyes: We all learn from the pain of being wrong once in awhile. The University, of hard knocks and lessons learned.
I just saw this thread and I don't actually run DCC. I understand it, because 1: I want to run it and I've done the research and 2: I am an Electrical Engineer and i'd be a pretty bad one if I didn't. I have no problems describing it. Others have also described it clearly. I rambled, because I like to hear myself post and as an opportunity to give others a chance to see a different metaphor. In reality, I don't think the type of power on the tracks matters AT ALL in a simplified explanation of DCC. Here, I'll give you a simple explanation. DC uses basic electrical concepts of voltage, resistance and current to both provide power and instructions to a locomotive. DCC uses basic computer and digital concepts to provide a larger number of instructions. The electricity on the track is both power to make the locomotives go and signals to tell the locomotive what to do with itself. This signal is complex like that in a computer or CD player or other digital device. The DCC decoder's job is to take this complex signal and extract the instructions (aka, tell the loco what to go do with itself) and then convert the electricity into that more basic DC concepts. How was that. Given a little time I could shorten that up to be more concise. No discussion of AC versus DC, because, at a basic level it is a waste of time. I describe it in terms people understand. Ohms law and "the magic smoke in my computer."
I did not intend to detract from the thread, I was merely trying to correct an incorrect statement. I don't see where this fits in this thread but since you brought it up, I don't see where we are "falling behind" in this hobby. For one thing, those systems are not well suited for the way most Americans operate. It seems to be more common for Europeans to sit at a central control station and operate their trains from there. Americans tend to operate by walking around following their train and carrying a walk around throttle. Another thing is most US DCC systems have been able to do most of what those systems can do for years by hooking them up to a PC. If you want to be able to draw a speed table on screen or have an on-screen representation of your track diagram, why do it on 7 or 8 inch screen when you can use whatever size PC monitor you want. One other thing is cost, for the cost of one of those fancy DCC systems shown(just the basic DCC command station with no accessories) I can have a US DCC command station with several walk around controllers
And in point of fact, given the market penetration of PCs, it's rather silly and wasteful to do it any other way. A PC will always be more powerful and have more options for GUI customization. I'm actually rather surprised there isn't a more robust use of PCs. I can only assume that the Venn Diagram of Model Railroaders and Open Source software users has a very very small convergence.
It won't match the AC voltage or frequency from a wall outlet because you can't throw the switch 60 times a second and the voltage will only be 24 volts peak to peak. However, the output would be AC. Changing the polarity at the track repeatedly would cause the current to flow in alternating directions hence it is alternating current (AC). I understand that you're trying to explain that the DCC signal is not the same as what comes from a power outlet but your definition of what is AC is too narrow. Both are AC but the not the same. The 12v DC from your Kato power pack is not the same as the 30,000v DC on the anode of a TV picture tube, but they're both DC.
I'd be more inclined to bet that the DCC manufacturers were reluctant to add the cost of a USB interface to their controllers, fearing that an even higher cost than the already stiff price would drive off too many customers. I also think they severely misunderestimated the utility of a connection to a PC...
The cost of a USB connector should be under $10 both for them and for the consumer. Any cost greater than that is pure greed.
Yeah, I know. I was trying to give them the benefit of the doubt. But I can totally see one of the managers saying "Hey, if we make USB an option we can charge $200 for it!" For the life of me I can't figure out why those interfaces cost more than $50, and that includes the low volumes and extra parts required by making them optional. And I'm still being charitable. Anywhoo... I'd better get back down off my soapbox.
At a bare minimum, I would have expected there to be a serial interface and that serial interface is one USB to DB9 dongle ($10 at Frys) from working on every computer. And yes, DCC is a racket. I have to hold my nose every time I think about it. But, whatchagonnado.
