Asymmetric DCC And How to Use It

The Digital Command Control waveform is symmetrical, meaning the pulses on Rails A and B are equal in amplitude. Asymmetrical means "without symmetry", meaning the amplitudes on Rail A and B are not the same.

To create the asymmetrical waveform, the DCC signal is fed through a special circuit consisting of four diodes in series, with another reverse biased diode connected in parallel. When current flows through a diode, a voltage drop of approximately 700mV occurs.

This results in the amplitude of the signal on Rail A being reduced by 2.8V.

A multifunction decoder with additional circuitry can measure the amplitude of the pulses on the rails, and compare them. This circuit will compare the two voltages, and if one is less than the other by a pre-determined amount, a signal will be generated and sent to the multifunction decoder's microcontroller. This will trigger the braking routine. Multifunction Decoders which support this feature are required.

Available Devices Supporting Asymmetric DCC

Current decoders that support this feature are:

• Lenz Gold and Silver
• All Zimo decoders
• ESU Loksound v5

If you know of any others brands please leave a comment stating which decoders.

Lenz offers the following Braking modules:

• BM1: Basic stop module
• BM2: Offers more sophisticated braking control for a single block
• BM3: Controls a series of blocks, initiating braking if the next block is occupied.
• LG100 Brake Generator

The brake module LG100 serves to provide prototypical slowing and stopping of digital locomotives in front of a 'red' signal. The LG100 generates the control signals for a booster, just like the command station LZ100. The LG100 does not have an amplified output for connection to the track. For operation, a booster such as the LV100/LV102/LV103 or LV200 is needed. Trains in both directions will stop.

When would you use this?

Asymmetrical DCC is not used on the entire layout. It is only used on short, isolated sections of track. The diode module often has a connection for a bypass switch, so the user can activate or deactivate this feature.

Example

This feature (if available) allows a fixed stopping distance regardless of vehicle speed. When activated, the locomotive will come to a stop, within the same distance. Pressing a Brake button or setting the speed to 0 trigger this feature. At slow speeds the result is prototypical.

An Automatic Brake Control section can be placed so that a train automatically comes to a stop in front of a red signal. When the signal turns green, a switch closes and bypasses the asymmetric DCC module. The train will automatically resume its previous speed using a pre-programmed acceleration curve.

For additional more in-depth information check out Asymmetric DCC and Automatic Brake Control on the DCC Wiki.

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Programming The Independent Brake in ESU Loksound

The author has installed several types of decoders in his locomotives including TCS WOW, Tsunami2, Loksound and others. All of these come with braking capabilities but not all are set up by default. The best example of pre-setup braking is the TCS WOW function F7. Press F7 once and braking is applied. Press again and the braking effect is increased. You can press a maximum of five times for maximum braking effect. The degree of braking with each step is CV programmable and the diesel programming manual is located here.  Brake programming is on page 22.

ESU Loksound v5 decoders have both independent braking and dynamic braking included. Version 4 decoders (including select) have dynamic braking by default and also include the independent brake as long as the sound file is equipped with Full Throttle features. A sound file that has the features will tell you in the file name, ex. 73450-LSSelect-Diesel-EMD-16cyl-645F3B-FT-V2-R2.esux. The 'FT' in the file name tells you it has Full Throttle features.

Version 5

We will start with version 5 since setup is different between the two versions. First take a look at the function mapping in the decoder pane and determine the logical brake function for the independent brake (usually F10).

Fig. 1

In fig. 1 the logical function attached to the independent brake is 'Brake 1'. Now that we know this we need to take a look at Brake Settings in the decoder pane. Go to the bottom of this page and you'll see figure 2.

Fig. 2

The brake functions are shown here by number and we're interested in function 1 at the top. This is the independent brake. There are two settings, reducing brake time and maximum speed. 

Brake time setting

The brake time reduction setting is tied to the deceleration CV4. If this setting is set to 0 then only the CV4 function determines how long it takes the engine to stop.  If this setting is other than zero then the stop time of the engine is reduced by the percentage stated. This is how it works as a brake. The stop time of CV4 will be reduced. You will have to experiment with these settings to get the effect you desire.

Maximum Speed setting

The maximum speed setting determines the lowest speed the engine will achieve with this function (F10) active. If you want the engine to completely stop when active then this setting should be set to 0.

Version 4 (and Select)

 In v4 decoders the independent brake is actually nothing more than a braking sound. To enable its ability to act as a brake start by looking at the function mapping the same way you do for v5 decoders. However, here's where the difference occurs. You 'll notice that there is no Brake function defined. Instead the logical function is blank. Click on it and select Dynamic Brake as shown in fig. 3.

Fig. 3

Now, again, look at Brake Settings in the decoder pane. Go to the bottom of this page and you'll see something different from v5 decoders which is shown in fig.4.

Fig. 4

Here you can see that the independent brake is actually implemented by the braking action of the dynamic brake.

One further point the author recommends you do is to add 'not F9' to the F10 function mapping as shown in figure 5. This prevents the two different brakes from interfering with each other when trying to start the engine.

Fig.5

These changes are not that difficult to make and one good thing about them is that these are all decoder changes. They have nothing to do with modifying the sound file. This means all you have to do is write decoder data which takes about 15 seconds not the 30 minutes of updating the sound.

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If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Digitrax is resuming repairs and replacements!

From Digitrax:

May 12, 1010

Digitrax is accepting items for repair again effective May 12, 2020. For the safety of your team, if you or anyone in your household has had COVID-19, please disinfect your items and packaging before sending in for repair.

If your warranty expired during the time this temporary halt from April 1 to May 20, your warranty will be extended.

We thank you for your patience.

-The Digitrax Team

Good news!!

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If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Athearn Roundhouse AC4400CW Release of April 2020 - SURPRISE!!!

What a surprise when I removed the shell from my new AC4400CW Roundhouse Locomotive that arrived the other day! It comes factory equipped with a 21 pin motherboard with speaker and function 3, 4, 5 and 6 contact pads! I love it! I became a 21 pin decoder convert a couple of years ago when Bowser released their NYS&W (Susquehanna) C420 Alcos. Also, unlike most Athearn locomotives, the frame is not powered. You can see in the picture both sides of the trucks have leads to the motherboard.

The motherboard comes with a 21 pin dummy plug which I removed. I put a piece of Kapton tape on the motherboard to insulate the ESU v4 Select decoder (soon to be a v5) I was going to add to the engine.

In the second picture you can also see the speaker pads (S+-) on the right side of the picture and 3 of the 4 function pads on the left side. I added a speaker and the programmed decoder, replaced the shell and I was off and running!

On thing that is difficult to do is add ditch lights. The engine comes with 2 dummy ditch lights below the front platform (non-prototypical) which could be removed and replaced with LEDs but there is no room! The front stairs block almost all access to them. There are ditch light kits out there but you will have to take a look and see what you think. It would be possible to add fiber optic cable to function as the ditch lights and there are kits out there for this also.

Regardless, I am having a ball running my new locomotive and I believe you will also.

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If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.