Digitrax Accessory Decoders

This section is covering technical information or issues relating to the use of Digitrax Accessory Decoders.  

(From Don Crano Email dated March 1st 2003)  Don is a Digitrax Guru but has passed away.

The Digitrax DS54 Stationary Decoder, is a 8 input 4 output decoder.  This combined with it powerful programming capacity and LocoNet feedback, make it one of, if not the most versatile accessory decoder on the market.  At the same time it is easy to use as a typical turnout controller.  Some of it's features are the 2 separate and individually programmable inputs, and it's 4 separate and programmable outputs.  Each input can be programmed for Trigger and Tasks, as well as broadcasting LocoNet messages to the system.

The basics are the track inputs must be connected to a boosters output.  This is where the DS54 gets it's commands from via system accessory decoder packets across the rails, and some power.  This connection can be made at the track in the local area.  

Note: If block detection is used the DS54 current draw will trip the detector.   It can be made at the booster, or a separate bus run for the DS54/s.  If you are using power management such as the PM4/PM42, you can use a circuit breaker section.  Or better yet a separate booster just for the DS54's.  This has the advantage of, if a short happens to trip out a track booster, caused by a improperly thrown turnout, the DS54 will still have power to correct the condition.  

The track connections on the DS54 are the two 6-32 screw terminals on the side next to the 4 [A/B/C/D] output jacks. 

Next you need to connect the output to what ever it is you want to control, turnout switch motor, etc.  Digitrax supplies these cables, they are typical Telco headset cables.  Each has 4 conductors, Red, Yellow, Black, Green. 

The Red conductor is simply another source for the Switch input of that output.
The Green conductor is the +common, this will connect to the common connector of your Twin coil type switch machines if required. 
The Yellow conductor is called the Thrown, and the Black is called the Closed. 

If you use static output for Stall motors, you will only use the Yellow and Black, do not connect the Green, and make sure it is isolated and out of the way.

Note: With stall motor type switch machines, Tortoise, SwitchMaster, etc. you can add pull up resistors to the output/s if more speed and/or more then one motor is to be controlled from a single output.   Resistors in the range of a min of approximately 470 Ohm's 1/2 Watt to max of 1.5k Ohms 1/4 Watt may be used.  Lower resistance equals more current, or faster movement.  Connect each resistor between the Green and Yellow [thrown] and between the Green and Black [closed] output leads.

The AUX power input, the large Red and Black leads from the DS54.  With twin coil type switch machines, and if you want more speed from your Stall motor types.  You will want to connect an 12-16 Volt AC or DC power source here.  This will increase the current available from the DS54 to throw the twin coil types.  This will also allows you to select the voltage you need to give you the speed you want from your stall motors. 

NOTE: the AUX inputs should be properly phased to the AUX power supply, this simply means that the Red and Black leads should be connected to the same AUX power supply leads with all DS54s.  If a DC power source is used, the + [plus] side must connect to the Red AUX input, and the - [minus] side to the Black AUX input.


The DS54 AUX input power source, must never connect to anything else on the layout, other then DS54's.  A single source can be used for multiple DS54 AUX input, but never connected to any other source or load on the layout.  The reason for this is simply the DS54 uses a halfwave input on the AUX, and the large Black AUX input is called the DS54 - or negative common.  This is not the same potential as the LocoNet Common, or just about anything else on the layout.  It is basically a semi quasi between the rails common.  All input voltage references are from input to this Black AUX or - common.

Also the single 6-32 screw terminal between the Local Panel inputs and LocoNet jack, is not a LocoNet Common, do not connect this to ground/LocoNet common.  This connector is the same as the DS54 - common or large Black AUX input wire.  It may be used as such, or an added connection point for interfacing the DS54 inputs if desired. If one does not understand this, do not connect anything to it.  This connector is marked the sensor common.

If you are using Stall motor type, like the Tortoise or Switch master, you need to set the output CV's to equal '20' for Static output.  If you are using twin coil types of the lower current draw of the Atlas or newer style Peco's, then the default of '00' should work fine.  If you have twin coil types that draw a little more current then these, then try programming the outputs to a slightly longer pulse, such as 0.25 or 0.50 seconds.  You do not want to send a pulse any longer then needed, so be careful here.

The DS54 is limited in the amount of power it can draw from the rails, you need to add the AUX power.   Are any of the large resistors mounted on the DS54 getting hot or starting to smoke, then there is to much current being drawn from the outputs of the DS54. 

The DS54 is limited to how much current it can supply to the outputs, something like 20-50 mA. continuous, 500 mA. pulse. 

This will cover the low current twin coils, or the Tortoise and Switch master stall motors.  These will only draw around 10-15 mA full stall.   If you are using something else, then you need to boost the amount of current the DS54 outputs can supply.  This can be done easily with the Digitrax DM1.  The DM1 plugs into a DS54 output and supplies up to 1.5 amps of current, 500mA. continuous, 1 amp pulse.  Other options are to add pass transistors, or use a low current draw relay to control the switch motor.  Or if you are using twin coil switch machines, you can add a CDU Capacitance Discharge Unit.  Such a unit can be built and added to the DS54, like this:  DIY CDU Design for DS54.


At this point if all went well and according to plan, you should have a working DS54.  That can be controlled from a throttle and/or computer.  If you would also like to have the DS54 broadcast messages in to the LocoNet, just connect the LocoNet cable. 

Note: the LocoNet connection is not required for DS54 normal operations.  But if you want LocoNet messaging [feedback] and/or cascade operations, then it must be connected.

Local Panel inputs is the JST 9 pin connector on the side next to the single 6-32 screw terminal.  And yes that is correct, it is the same 9 pin JST connector found on most HO standard decoders.  As noted prior, the DS54 is an 8 input, 4 output device, so we have two inputs for each output.  The White wire is a handy greater then + 6V source.  The ON state of a DS54 input is considered any voltage from - common that is greater then +6V, this can easily be supplied by the White wire.  Note the White wire should not be used as a current source, only a greater then +6V Voltage source for DS54 input ON voltage.  If all is well at this point, you can also, if the DS54 inputs are still programmed to defaults, check the local panel inputs out.  Just take either of the two inputs for any output, [Switch or Aux] and with the White local panel wire, momentarily touch it, the output should toggle positions each time it is touched.

The inputs are defined as AUX and SWItch. For the most part they can be considered the same, or simply used interchangeably, except for some certain applications, such as Exact Turnout Position, etc.  This is why the Red output wire on the output cable is the same as the Local Panel Switch Input for that output.  Other wise you may use them for Detection input, pushbutton, or use both inputs for toggle switches, etc.  The inputs are as follows:

Orange = AUX A Blue = Switch A
Black = AUX B Violet = Switch B
Yellow = AUX C Gray = Switch C
Green = AUX D Red = Switch D