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BitSwitch Asymmetrical and DC Brake Generators

Posted by on Dec 11, 2015 in Tips DCC Components, Tony's Tips |

I’m interested in the Asymmetrical and Set Speed Zero BitSwitches.

  1. For the set speed zero no other commands can be used, this includes horn, light and engine rev’s?
  2. Do Lenz and ESU both have Asymetical capability?
  3. There is a website with a diagram from the DCCWiki and it shows the junction which bypasses an asymmetric generator (see image below).  Can this bypass circuit damage an Asymmetrical Brake Generator?
  4. I’m using PRR position light signals. Is slow approach available without using Lenz?
  5. Will any problems be caused if I use metal wheels for shunting purposes on the rolling stock?
  6. Will the 4 Way Crossing BitSwitch work with CV3 and CV4?

Asymmetric Generator Bypass Circuit

  1. When the brakes are applied in a block, different brake generators behave differently.  When the brakes are released, the train is under control of the main DCC system.  When the brakes are applied using an asymmetric brake generator, a decoder that recognizes this signal will execute all commands sent to it except speed change commands.  Actually, the decoder will read the speed change commands but will not output any drive to the locomotive motor until the asymmetrical signal is removed.  When the signal becomes symmetrical again, the decoder will execute all commands including the last speed command sent to it and speed control will revert back to the main system DCC controller.  When the brakes are applied using the set speed zero generator, all DCC commands sent to the locomotive are blocked and replaced with a universal broadcast code that stops all engines in that block.  Thus, any command sent by the main DCC system controller to the locomotive while the braking function is enabled will not make it to the decoder in the locomotive.  The brakes are released by reconnecting the block from the set speed zero generator to the normal DCC signal from the main system DCC controller.
  2. ESU’s documentation states that the newer Loksound Select and V4.0 decoders can be enabled to stop on either DC signals or asymmetrical DCC signals by setting CV 27 to the proper state.
  3. Connecting the input to the output of an asymmetrical DCC brake generator does not damage the unit.  It effectively disables the unit, passing the symmetric input signal from the command station directly to the tracks. The components do not amplify any signal and are essentially passive.
  4. The BitSwitch products do not support a slow approach.  The trains accelerate to the speed set by the system throttle setting using CV 3 in the decoder to determine the acceleration rate.  When the decoder sees a braking signal, it decelerates according to CV 4 in the decoder to speed zero.  There is no method supported to move to an intermediate speed setting.
  5. The BitSwitch products allow for metal wheels to shunt the insulated rail gaps. When using BitSwitch circuits, the placement of the insulated rail gaps in the layout should occur at specified locations so the adjacent blocks are connected momentarily by the metal wheels and will have the same DCC signals on them. Otherwise, there could be momentary shorts that cause circuit breakers to trip or unnatural pauses in the train motion or train sound systems.  BitSwitch controlled layouts specify where the gaps should be placed to prevent this kind of problem and are dependent upon the length of the longest trains to be run and the stopping distances for such trains.
  6. The 4 Way Crossing BitSwitch is designed to handle bidirectional traffic.  Normal control using other BitSwitch circuits requires traffic in one direction.  So integrating a 4 way crossing into a larger layout with other BitSwiches cannot be done without the design of customized circuits that do not exist today. We have no plans to support such a method.  If you use the standalone circuitry of the 4 way crossing, the starting and stopping of trains are controlled by CV3 and CV4 settings in each of the decoders of each locomotive that uses the crossing.  The changes to the CV4 setting determines how quickly the train will stop and sudden or abrupt stops can derail a train but requires less stopping distance.  Likewise, CV3 should be set to accelerate the train smoothly for reliable performance. No other CV settings are required for this to work, other than the normal settings to make the train operate under DCC control.

The BitSwitch circuits are triggered by a normally open reed switch that closes momentarily when a locomotive passes over it with a strong magnet. This completes a circuit that connects a latching relay coil to an internally generated voltage on the BitSwitch card to close the circuit.  If you wish to connect the BitSwitch relay coils to other logic for this function, an analysis of the circuit must be made to determine that the replacement logic that drives your existing signals behaves the same way as a switch closing momentarily and that the voltages that are present will not cause unintended side effects.  Typically, we just add dedicated reed switches under the tracks to operate the BitSwitch relays.  Without knowing your circuitry, I really cannot determine if a BitSwitch will work when connected to it.

The most cost effective solution for braking is the use of the asymmetrical brake generator if your decoders support that method.  Using the set speed zero method requires a more expensive BitSwitch brake generator and a DCC booster unit which can cost hundreds of dollars for all of the power sources and circuit protection circuits.  The set speed zero unit is for folks who have decoders installed that do not work with asymmetrical brake generators or DC brake generators. The modeler has to determine if changing decoders is less expensive than adding the set speed zero brake generator and associated circuitry. We can support any of the 3 methods of brake generation and can give you a quote for a system to fit your needs if you desire.

Lenz owns the patents concerning asymmetrical DCC and only a few decoder manufacturers are licensed for this technology. TCS does not list braking in the presence of an asymmetrical DCC signal as one of their supported features so it is fair to assume that their decoders will not stop in the presence of an asymmetrical signal.