Sunday, December 23, 2012

Building a Digitrax LocoNet tester

This is going to be another one of those posts where I wander a bit from the installation of DCC decoders but  this is good stuff to know if you use a Digitrax system and it ended up being a fun and easy project.

The little device in the photo on the left is called an LT1 and has 4 green 4 LED's that when lighted after being plugged into the Loconet indicate all is well.

Because the weak links are the flat telephone type cables and the rather delicate connectors it's important to have one of these on hand to verify that the connections are sound.

The LT1 comes with the system and they can also be purchased separately and they are not expensive.  The problem is that they are very small and easily lost.  They are also a goner if they get stepped on which can easily happen at a show if left on the floor.  I have had a couple of these and so has the Ntrak club I belong to but the last couple of show setups none could be found so I decided to try to make something that was a little bigger and not so easily lost.

I found this photo on wikipedia that shows the pin outs of the phone connector and what they represent on the LocoNet cable.

After a couple of experiments this is what I came up with.

I used a surface mount RJ11 phone jack that had 6 contacts.  These are about 2 inches square and about 1 inch thick.  Still small enough to easily fit in the toolbox but large enough not to get lost so easily.

The LED's are actually LED light boards from Atlas GP7 locomotives which in I had installed TCS CN-GP decoders in.  I re-mounted the LED's so they point straight up from the board.  I also used scraps of decoder wires to make the connections inside the box so this was really a junk box project.

Here is a look inside.  The back part and the cover of this phone jack just snap together.

The LED boards were modified by re-mounting the LED so that it is pointed straight out from the board.  Also I trimmed down the size of the boards so they would fit close together in the middle of the cover and stay clear of the screws on the back part.  The yellow and black wires are the commons so they each connect to two of the LED boards on the side that does not have the resistor. The other four wires are each connected to the side of the boards that does have the resistor.  Each of the wires are then placed under the screws.

Parts List:
  • (4) LED boards from Older Atlas GP7's.  Similar boards would also work
  • (1) RJ11 surface mount jack - widely available for about $1.00 each

The way to use this device is to get the command system going so that a train can run.  Then plug one end of a loconet cable into the command station and the other end into this tester.  All four LED's should light up, if they don't then there's a bad connection in the cable or at one of the connectors.  Re-installing a new connector often corrects the problem so a good quality RJ11 crimper and connectors should be kept in the tool box.

When setting up the DCC system on our Ntrak layouts, I have found the the telephone cords to often be unreliable so I will test each section of cord before actually using it to connect the command station to the various panels on the layout when setting up.  This method avoids much frustration.

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