DCC Misinformation Debunking

This page is under construction and needs updating as the DCC Wiki has been seriously improved.

Typical misinformation:

DCC is not AC but DC
DCC is not bipolar
DCC track voltage never goes to zero
my $5 voltmeter reads DCC track voltage just fine.

DCC Wiki

My overall advice is that this is just like the Wikipedia, but worse. You have too many people putting information forth as facts, when they are often opinons.

Worse, while the Wikipedia almost always has lots of references, the DCC Wiki has none.

The intro is good, and a good page to read on basic concepts:https://dccwiki.com/Introduction_to_DCC

Note: previous incarnations of this Wiki were awful, it's been a lot improved.

Twisting track power wires

The DCC Wiki starts off well enough:

"This topic is fiercely debated on internet forums and DCC-related mailing lists, endlessly and without any real conclusions. This article tries to provide concise reasoning for either. "

https://dccwiki.com/Twisting_Power_Bus_Wires

But before getting to the reasoning, the BS starts:

This hell right away, stating:

"There is always a large debate on the twisting of track power bus wires. Keep in mind that DCC power buses are an 'Unbalanced Pair' - one wire (A) is held to ground while the other (B) is energized, then they flip when A carries a signal and B is held to ground. This is happening constantly and at a high rate. "

Complete crap. Spent several days arguing this with a person recently.

Yes, if you are INSIDE a DCC booster circuit board, you can typically measure from the internal ground to one of the 2 output connections, and you will see it go positive and negative, BUT THERE IS NO GROUND OUT ON THE LAYOUT, THE TWO RAILS ARE CONSTANT ALTERNATING IN POLARITY PLUS TO MINUS AND BACK AGAIN THIS IS THE VERY DEFINITION OF AC (ALTERNATING CURRENT).

Complete insanity. Not only is this a balanced pair, but this is WHY twisting wires helps reduce interference from outside sources and why twisted pair has been used from telephones to Ethernet wires for data.

I have only been able to determine that this idiocy has come as a necessary support for some other misinformation.

Look at the many examples of DCC waveforms on an oscilloscope, it's clearly a bipolar square wave.

Other than this BS, the DCC wiki does an OK job of identifying pro's and cons of twisting. They should have stopped there.

Back to twisting the wires:

Inductance

So a benefit given for twisting wires is that it reduces inductance.

(aside, having inductance in a DCC power circuit "rounds off" the sharp corners of the square wave, which is not the desired effect. Additional inductance would normally reduce high frequency noise, if the right inductive value. In general you want to minimize inductance)

So, it is known that to minimize inductance is to place 2 wires of a balanced pair (we have established this is a balanced pair) closer together. So the basic "common wisdom" is that twisting together will keep the wires closer, and thus minimize inductance.

That is indeed true... but in general, twisted wires will increase inductance since twisting significantly uses more wire, so often the inductance INCREASES.

But, the "experts" then recommend just a few twists per foot, like 2 or 3. So, that is reasonable for HO trains. It probably does little harm at worst case, and MIGHT help installations where the 2 main DCC wires can get far apart.

Noise reduction:

An external magnetic field can induce voltage in a wire. Basic law of physics. How magnetism is generated in a motor. So a wire or other device close enough to your DCC wires can induce an unwanted voltage, and this is generally called "noise".

You see telephone wire, and more recently Ethernet cables made of twisted pairs. Any magnetic field that hits a twisted pair will induce a voltage in the wires, but since each wire is twisted in a different direction (one clockwise one counterclockwise) the voltage in each wire is equal in magnitude but OPPOSITE in polarity, and effectively cancel each other out. This is called common mode rejection.

All is well here, except that the number of twists needed is way more than the "common wisdom" Look at an Ethernet cable, open it and convince yourself.... don't listen to "experts". The people making these cables know what they are doing, since Ethernet works.

Bottom line:

I think the best way to approach this, is keep your wires close to each other and away from other stuff. If you have issues, you can try moderate twists, but I would reposition wires and look elsewhere first. At these frequencies, a cheap oscilloscope can be had for very little money. LOOK at the waveform yourself and you can stop guessing. You can see directly what the issue is from looking at the ACTUAL waveform.

For garden railroads, most people use twin lead landscaping wire, where the 2 wires are nice and close (and consistent) and will do perfectly fine. My wires are separate 10 gauge wire used for wiring 220v circuits in a house, but in conduit. Runs up to 60 feet. No issues!

Back to the DCC Wiki on twisting wires:

Well they should have stopped there, with the pro's and con's.

But it continues with this:

DCC Issues... most make sense, but some seem nuts.

"Excessive track bus impedance can cause a multifunction decoder's PWM pulses to be superimposed onto the DCC signal, distorting the DCC waveform."

I'm going to research this.. seems nuts... how can the PWM get BACK from the H bridge, through the full wave bridge, back into the rails? Seems completely nuts, driving voltage backwards through a full wave bridge into the rails? How can that be?

They rest are fine, but I'm going to find the person who wrote this and ask him where he got his data.

Noise:

I think this is by far the bigger problem over the inductance in your wiring. Noise get in by a magnetic field. This can come from a nearby wire carrying heavy current (making a strong magnetic field) or possibly motors, or something putting high frequency noise IN THE DCC CIRCUIT. There are some possible outliers, like having an RF transmitter nearby and one of your wires is a "tuned length" for that frequency, but this is rare.

Titan advanced function mapping

Note: page numbers quoted are from the latest QSI manual, version 5.2.0

So, in several documents, the Titan is supposed to support function buttons higher than the NMRA standard mapping of F0 through F12.

But the only documented mapping tool is the NMRA mapping table, CV33 through 46. (page 66)

NMRA Function key mapping

The NMRA mapping allows mapping QSI "features" to a function key for F0 through F12. This table also allows mapping more than one item to a Function Key. Usually you can map up to 8 different items to that Function Key. This allowed a person to map for example the horn and ditch lights to a function key.

These are CVs 33 through 46 (page 66)

A reasonable idea when you basically had only maybe 6 outputs on the decoder.

When sound came around, manufacturers extended the use of the table to include sounds as well as the physical "function outputs" on the decoder.

Since you can (usually) map up to 8 "things" to a Function Key, that suffices for many situations.

Titan extensions to mapping

QSI added an extension on how things work in a Titan (and some other Quantum decoders)

There is a list of "Features" in a Titan, which includes sounds and other things, and these are indeed called "Features" but unfortunately are often abbreviated like: F12, where people think it is Function Key 12, when it is actually Feature 12.

There is a list of Features (but not complete) on page 121. The Features have a "Feature ID" number.

There are some more Features listed in a different way on page 126, the defaults in most Titans: like Feature ID 62 - System Volume increase.

Note well, that lighting can be specified as in a group, called Multiple Automatic Lights. There are 3 such groups.

You can specify what lighting outputs (up to 12 lighting output ports, shown on the board pinout as LED1 through LED12) are in what lighting groups.

So:

You can group lights into one of 3 groups
Then map features to what QSI calls Outputs which are NOT the same as the physical LED outputs on the decoder
Then map Outputs in the NMRA function mapping "table" using CVs 33 through 46 (page 66)

Note that you can assign up to 8 different "Outputs" to one Function Key, with some restrictions (you see grayed out selections on the NMRA "table"

Note very well that QSI admonishes to NOT map the same "Output" to different keys, it will result in erratic behavior.

"Hidden" QSI Function Key mapping

I noticed (and others have too) that QSI indicates "default" Function Key mappings for (some) Function Keys above F12 (the limit in the NMRA table)

This is in the manual, page 126, but there's more "sprinkled" through other QSI documents, often the user guide packaged with the decoder.

Below is a list that is MOSTLY correct: (I'll try to make it more correct/complete) (I've also tried to correlate the QSI Feature ID where I can:

F11 to toggle between the primary and the secondary horns. (After pressing F11 once, F2 will operate the secondary horn in the normal way.),
F13 to decrease System Volume by 2 dB, feature 63
F14 to increase System Volume by 2 dB, feature 62
F15 to play the Grade Crossing horn sequence (long, long, short, long), but only when the locomotive is moving, feature 154
F26 to start the Fuel Loading Scenario (dialog and sounds appropriate to fueling with diesel oil), but only when the locomotive is stopped,
F27 to start the Maintenance Scenario, but only when the locomotive is stopped,
F28 to start the Water Loading Scenario, but only when the locomotive is stopped.

So by interrogating the QSI Output mapping CV53.PI.SI I found that indeed you could change the SINGLE feature assigned to function keys 13 and up

Note CV53 has 2 settings, one for when it is in FWD or REV, and the other for Neutral (NFF and NFR)

The Outputs run from 1 to 30, so I started by looking at Output 30, and indeed found it was mapped to "Water Load" for F28 (only in neutral)

Continuing to investigate, it seems that Output X gets mapped to Function X-2

F28 = CV53.30.1 = 147 - water load - F28

F27 = CV53.29.1 = 148 - maintenance - F27

F26 = CV53.28.1 = 146 - fuel load - F26

F25?? cv53.27.1 = 10 short air letoff

F24 ?- cv26

F23? - cv25

F22? - cv24

F21? - cv23

F20? - cv 22

F19? - cv21

F18? -cv20

F17? - cv19

F16? - cv18

F15 - cv53.17.1 =

F14 - cv53.16.1

F13 - cv53.15

F12 cv53.14

- cbell is feature 3

horn 1

from my testing, it appears that FKEY 28 is mapped to output 30

So far I have not tested all of the function keys, but it seems to work.

Note well, you can only map ONE Feature to a Function Key this way (as opposed to using the NMRA Function Key mapping for F0 to F12

QSI programming fixtures

Programming hardware setup

Below is a simple setup with a motor and speaker and the socket. I'm holding a connector that lets me use the speaker plug on the Revolution (by the "I" in QSI on the programmer dongle) or change to a couple of wires that let me screw in to the Titan terminals. Al this is on a small board, the speaker is in the top of a spray paint can.

bench power2

A more sophisticated setup below. This one has a socket and also DIP headers to screw into Titans that have had their pins cut off. Notice that I have both speakers there to confirm programming between them.

At the front you can see the jack for power and the usb socket.

Inside, I just removed the programmer from it's housing to make an easier installation into the box, but you could leave it in the housing and just cut a bigger hole in the cigar box.

Installing and using Quantum Upgrade

This page is all about installing the USB driver for the QSI programmer, and getting it working

Installing the QSI programmer and driver

Overview:

The programmer has a USB interface, and here are some tricks to installing the driver. This is because certain versions of the USB driver are not "signed" and Windows won't normally allow this.

In addition, there are some cases that certain versions of the user software (the program to load sound files, and the JMRI-like configuration program) need DIFFERENT versions of driver and this also interacts with the Windows operating system version. Fun huh?

Installing on XP

Installing on Windows 7

Installing on Windows 8/8.1

Installing on Windows 10

Installing on Windows 11

Installing the hardware driver on Windows 8 / 8.1 / 10 / 11

This can be a real pain in the ass. The driver needed seems to vary also with the version of the CV Manager software

Do not plug in the dongle! You need to install the software first!

The driver will not install on windows 8 or 10 with the normal install. Part of this is because it is unsigned, and Windows 8 and 10 won't allow this by default. The other part of the difficulty is that it needs to be installed in a troubleshooting / compatibility mode for windows 8/8,1

First, have the silabs driver already downloaded and in it's own subdirectory (unzip the file). The file I use is from the QSISolutions site named: qprog_usbdriver_winxp_3_2.zip

Now, you need to put your computer into a special mode to accept unsigned drivers. This mode is called "allow unsigned drivers" You will set this up, the computer will reboot, and after installing the driver, this special mode will go away after the next reboot. Note well: if you don't get the driver installed and you reboot, you need to start the procedure over.

Please note: some newer versions of the programs may need a different driver, I found this on the newer CVManager. Since I use the Titan ET features, I use the older driver.

Driver versions vs o/s and CVManager versions

On windows 11, and latest QSI programs, Silabs CP210x USB to UART Bridge, version 10.1.10.103, dates 1/8/21

Put computer in the mode to allow unsigned drivers (windows 10):

One way is to do this is:

Open the action center (you should know what this is otherwise google it)
go to all settings
then update & security
then recovery
then advanced startup.

Your computer will reboot, and then after some time you will be prompted with a menu with following options.

Continue
Troubleshoot
Turn off

Choose Troubleshoot

Then the following menu appears:

Refresh your PC
Reset your PC
Advanced Options

Choose Advanced Options

Then the following menu appears

System Restore
System Image Recovery
Automatic Repair
Command Prompt
Windows Startup settings

Choose Windows Startup Settings, then Click Restart.

Now the computer will restart and the boot menu appears.

Choose: “Disable Driver signature Enforcement” from the menu. Now windows will start and you can do the installation of the driver that is not signed.

Windows 8 procedure:

Here is a link to the procedure for Windows 8 with pictures: http://www.craftedge.com/tutorials/driver_install_windows8/driver_install_win8.html

(why in the heck are you still running windows 8?)

Earlier windows:

You can install the driver on XP, Vista and Windows 7. Nothing special, except there is/was a different driver for Vista 64 bit.

Now to install the driver (windows 10):

Sometimes you need to log in as the actual local administrator user. By default, this user is often disabled. Google "enable administrator user windows 10"

I still do the troubleshooting way, but some people can directly install from here.

Clearly, navigate to the folder where you unzipped the driver.

Then right click on the installer executable: QP_USBXp_Installer.exe and select "troubleshoot compatibility"

I pick the "troubleshoot program", then tick the boxes for "earlier versions of windows" and "requires additional permissions"

On the operating system selection, I pick Windows 7

This is pretty much the most bulletproof method. Sometimes you don't need all of this, sometimes you do.

Once the software installs, THEN plug in the programmer

If you get stopped from running the program, you can change the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\EnableLUA to 0 in regedit. you will probably have to reboot.

For using the 3.0.0.18 CV Manager, the usb driver I have installed is a USB device, called "Quantum Programmer", version 3.2.0.0, with a date of 2009_11_1

Using/debugging programmer after driver installation: Firmware version/upgrading

You need to install the software driver first, which makes the programmer available via a "COM" port. The following sections address the selection and installation of the driver. DO THAT NEXT, and then come back here.

After installation, you should check for upgrade of the firmware in the programming "dongle" at least when you get one. It's in a really weird place in the programming software.

right click on the upper left of the title bar of the Quantum Upgrade window, right on the words "Q2Upgrade"
Yes, there is nothing up there, but when you do it, you get a menu you cannot get any other way.

Capture2

Now click on "Quantum Programmer...", click that, and then you get another menu.

Capture3

Click "retrieve firmware version".. you will then see the version in your dongle. If you get nothing back, then you are NOT communicating with the dongle, or it is dead.
Also check "get error status"
If your firmware version is not 2.0.5, then you should be able to upgrade the firmware. This is the latest firmware as of 2021

Now if everything is good so far, we can check the "final stage" of the programmer, the connection to the decoder.

Click on the "Diagnostics..." menu
now you get the menu below:

Capture4

Click the "Measure Baseline Current" button.
You should see something between 2 (decoder only) to about 15 (maybe some lights)
ZERO means that there is no connection detected, either you are not connected to the decoder, or the output of the programmer is bad (broken)
very high, like over 100 means you have a dead short (either short circuit across the output, or the programmer is bad or the decoder is bad.