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DCC Basic Concept And Understanding - Electrics - DCC - Getting You Started. - Your Model Railway Club
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 Posted: Sun Dec 9th, 2007 08:48 pm
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henryparrot
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I am writing this post for any members that are considering DCC or perhaps already have it and do not understand how it really works.
I will try to put things in terms which most people should understand using analogies where appropriate.
Now this is going to be basic concepts so at this stage I intend to keep things very simple and not go into complex layouts to confuse anybody.
I will probably add to this post over a period of time so if you are interested you will have to pop back for the next instalment.

DCC means Digital Command Control it has nothing to with direct current which we call our dc controllers.
OK, with our DC controllers we run 2 wires to the track and we put a loco on it, we select the polarity + or - with a switch which chooses the direction the loco travels in. We then turn a knob which increases the voltage up to roughly 12 volts this controls our speed, variable between 0 and 12 volts.

With DCC you can still have 2 wires running to the track from the controller/base-station the first difference is that full voltage is on the track all of the time so its as if your controller was left full on all the time.
Now with DCC you have decoders in each loco. Each decoder is really like having a controller in each loco which controls direction of travel speed of travel and any other functions that may be on the decoder.
So really think of a decoder as a Gaugemaster controller stuck inside each loco.
So if on our imaginary layout we have 2 locos 1 is Thomas the tank and 1 is Gordon the big engine.
Both locos have a decoder fitted in them.
With your DCC controller you give them a unique address so Thomas is 4 Gordon is 6.
Now what you do is put both locos on the track then with your DCC controller you select one of the addresses lets say number 4 =Thomas
You then press the accelerate button and your hand controller this tells the controller (Decoder) in Thomas to move forward to speed set on your DCC hand controller. Thomas then does as he told by the decoder and moves forward at the speed he has been told.
Thomas is now going around merrily on the Track.
Now we put Gordon on the same track ( I know they would crash but bear with me). On our DCC handset we select number 6 which is Gordon, we then press the accelerate button and of goes Gordon on the same track as Thomas.
Now remember that each loco has its own controller (decoder) so we are able to run Thomas and Gordon at completely different speeds if we want to, because the controller (decoder) controls how much power and what direction the motor turns and we humans send messages with our handsets to the decoders telling them what we want them to do.
If we want a deliberate crash we select 4 Thomas and with our hand controller select Thomas to travel in the opposite direction (imminent crash)
With most DCC systems the only limit to how many locos you can run on a layout at the same time is governed by your Base-station / Transformer so if you had a 3 amp transformer you could probably run at least 8 locos at once.

That is a very basic explanation I intend to explain next how the information gets from your DCC handset to the decoder in the locomotive.


How the information gets from your handset to the decoder.

DCC works in a very similar way a computer network or the Internet works, all information is contained within things called packets - millions of them that are sent between one computer to another. I now intend to try and de-tech this so anybody can understand. I should point out that to operate any DCC system you do not have to understand this next section at all, but I thought I would write it so if interested you would know roughly what is happening when you press the buttons.

OK, the way a DCC system communicates is very similar to the way you send a standard letter through the Royal Mail system.
The first thing you do is pick up an envelope, on the front of the envelope your write the address where to send it to.
You then get a piece of paper and write whatever note or instructions you want to include in the letter.
You then put the letter in the postbox and the Royal Mail take it to the sorting office and it is then given to a postman who runs around to find the address on the letter when he finds it he pushes it through the letterbox.

Now on your DCC system think of your handset as a pen and paper you first write the decoder address 4 (Thomas) on the envelope. You then write your letter telling Thomas to move forward at 10 mph.
The letter then goes to the DCC base-station (sorting office).
At the sorting office the letter is then given to a postman who then runs around your entire layout with the letter looking for number 4 (Thomas)
When He finds number 4 (Thomas) He hands the letter to the decoder inside Thomas, which opens the letter and carries out the instructions in the letter by making Thomas do exactly what the letter says, move forward at 10mph.

Now in very basic terms that is what happens, if you have understood that bit above I will try and put the above in DCC terms.
So when you use your handset you are actually writing directly into the base-station. What I have called the envelope is really called a packet. These packets (envelopes) are created inside the base-station.
A packet in reality is a pulse of electrical signals but just think of it as an envelope . So on the front of the packet the address is written (4 Thomas)
Inside the envelope the instructions are put move forward 10 mph.
Also in the envelope there is a checklist that makes sure when the packet (letter) reaches its destination its contents read correctly (error checking).
Now all of these packets (letters) which are really electrical pulses actually travel at lightning speed and the entire postal system occurs in millionths of a second. For now this will give you a basic understanding as there are more things to packets and the tech minded would probably pick flaws in my overall description but in essence it is correct.
But as I have said you do not have to understand the above but if you do you can understand what is happening when you press the buttons.

Next instalment what are these CV things they keep talking about.
 
OK  next instalment.
Reality check - some people know their decoders have cv`s but never actually try to adjust them, in theory and also 99% of the time in practise, once you have fitted a decoder in a loco your loco will run fine and do exactly what you tell it to do with your controller and never have cv`s adjusted.

Cv`s or Configuration Variables - big technical word isn't it.
Well what does it mean? Basically it's things you can switch on and off or you can adjust - that's it. Tecno blurb really
All DCC decoders have cv`s and there can be quite a lot of them dependant on the decoder manufacturer.
Also some decoders allow you to adjust more cv`s than others
When you buy a decoder there is an information sheet that tells you what cv`s are adjustable.
Generally there roughly 3 types of them.
There are ones that you can just read information from i.e manufacture info or ID that will tell you who makes it and what model it is.
Another type are ones that you can set to switch things on and off
i.e. have shunting top speed on a function button or not
Another type is adjustable between 1 figure and another say 1-255
i.e. Adjust acceleration 1 -255
All decoders have factory set defaults which are set to a generic figure that should work fine with most locos.
Now, when people feel confident they will start to have a little play. Don't worry though, there is a reset cv that restores it to factory defaults if things don't work as expected.
Somebody may try and adjust the acceleration rate to what they feel the particular loco would do in reality for example.
There are many adjustments and can be quite absorbing finding your best settings for each particular loco.
This is just a rough explanation so I am not going to go into depth with this .
As an example, although you unfortunately do not find many of these tables on the net below is a link to Johns Bromsgrove site where he has put cv adjustments for certain decoders in certain locos which either himself or somebody else found best for it, but bear in mind sometimes some of these settings can be personal preference.
Remember this is an example, please don't think you have to adjust cvs because you do not have to and you can just adjust a few if you want to
http://www.bromsgrovemodels.co.uk/Decoderscvsettings4mm.htm


10/12/10

Other things that are different with DCC are that the decoders in the locos allow other things to be used in the loco.
On a standard DC system anything fitted with lights is not that convincing as the light brightness is tied to whatever the setting the controller is so if you loco is crawling its extremely dim and is only bright when you have the loco running faster and the brightness goes up and down with the controller setting.
With a DCC system the lighting is set at a permanent voltage so the light brightness is constant all the time and with the cv things you can actually adjust the brightness of the lights yourself.
Your are also able to turn lights on and off with the controller plus when the loco is say a diesel the lights are automatically reversed when the direction of the loco changes.
There are also other lighting things you can do like have flickering smoke boxes on steam locos if the Decoder supports that function.
Other decoders have sound capability which gives you another avenue of the hobby to pursue.
Of course there is the ability to use other things as the decoders have function outputs which means that its capable of switching and adjusting other things so you could have things like smoke units fitted which you could switch on and off and some people have made DCC uncoupling arrangements.
Modellers imagination is the limit here, as you could add whatever you wanted to be switched or adjusted on the loco as long as its within the actual decoders power handling capability.

DCC things other than locos
As well as the engines your DCC system can be used for other things.
For example your points/switches can be switched using your DCC system.
The most common way is you have a unit called an accessory decoder usually has a number of outputs which go to point motors a common one would have probably 6 outputs, so that means it will drive up to 6 solenoid type motors.
The unit is connected to the DCC system in various ways and each point is connected to the accessory decoder. Then on your controller you can assign each point a number or name and all you do then is press the appropriate button to operate the points.
How this is done on different DCC systems varies, some are just press a button and it switches, some are more informative and actually allow you to set routes etc.
You will note the word accessory decoder, that means as well as points other items like signals etc can be switched with these units.
Plus there are different types of accessory decoders that can be used for different things.
cheers Brian

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 Posted: Mon Dec 10th, 2007 12:37 pm
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Wayne Williams
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Very interesting Brian, I will await your next lesson!

Wayne



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 Posted: Mon Dec 10th, 2007 04:17 pm
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phill
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What a kind man u are, very interesting, look forward to next lesson mate.
Phill

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 Posted: Mon Dec 10th, 2007 07:19 pm
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Matt
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henryparrot
when i started i needed someone like you to explain the simple way of doing things :D

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 Posted: Mon Dec 10th, 2007 08:09 pm
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Gosh Brian

Even I can understand it now :D

Keep up the good work

Bryan

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 Posted: Mon Dec 10th, 2007 10:38 pm
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MikeC
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DCC Parrot Fashion aka DCC For Dummies :D

Extremely helpful, Brian, and easy to read. Please keep this going.

Mike

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 Posted: Mon Dec 10th, 2007 10:41 pm
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Wayne Williams
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I'm still with you Brian. Keep em coming.

Wayne :D :D



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 Posted: Mon Dec 10th, 2007 10:47 pm
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Gwent Rail
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The easiest way to tell us about an update, Brian, is just to post a reply in the original thread. That way everything stays together.
To avoid confusion, I've deleted your advisory thread and announced it here.
Hope that's OK

Note. Updated Information Has Been added to the First Post in this thread.

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 Posted: Sun Dec 16th, 2007 10:10 am
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BromsMods
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There is a table at http://www.bromsgrovemodels.co.uk/TCSDecoderscvsettings.htm#CVSettings which shows CVs and their usage on TCS decoders - the table is geared towards TCS decoders but also shows CVs that are common across all decoders (or should be!!). Do remember that certain CVs have different applications on different makes of decoder.



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John Russell
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 Posted: Sun Dec 16th, 2007 12:43 pm
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Robert
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First Post updated again.



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 Posted: Wed Dec 8th, 2010 11:48 pm
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xdford
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Hi Brian,

I don't know that much about DCC either but this explanation I have forwarded to a returning hobbyist ... he may as well be a "newbie" ... and it seems as good as any I have seen. Well Done

I also found this site  http://www.members.optusnet.com.au/nswmn2/DCC.htm which may be also of some assistance to all of us... eventually!

Cheers

Trevor

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 Posted: Thu Dec 9th, 2010 02:37 am
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John Dew
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Great thread Brian ........nicely done



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 Posted: Thu Dec 9th, 2010 07:50 am
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owen69
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xdford wrote: Hi Brian,

I don't know that much about DCC either but this explanation I have forwarded to a returning hobbyist ... he may as well be a "newbie" ... and it seems as good as any I have seen. Well Done

I also found this site  http://www.members.optusnet.com.au/nswmn2/DCC.htm which may be also of some assistance to all of us... eventually!

Cheers

Trevor
Trevor, nice find , but it is already in the index !!
:cool wink:lol::cool:

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 Posted: Thu Dec 9th, 2010 09:22 am
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henryparrot
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Gosh 3 years ago when i wrote that

Actually i may add to that now i had totally forgot about it

Brian

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 Posted: Fri Dec 10th, 2010 10:46 am
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henryparrot
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Just added a bit more to the original

Brian

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 Posted: Sat Dec 11th, 2010 06:43 pm
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Diesel
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Very good Brian it,s good to have it explained in plain english , i,m using DCC for N gauge and it,s working great :thumbs but havn,t attempted to alter cv,s yet .



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