Atlas Signal System and DCC
I had installed a couple of the Atlas Type "G" Single Target signals using the Atlas Signal Control Board (SCB) along with their Analog Block Detector. They worked fine and I was really excited with the operation of the signals. Running a long freight train one evening through the block that one of the signals was covering, I noticed a huge drop in the speed of the train. At first I thought it was because of the length of the consist. It was only 15 cars long being pulled by 3 Atlas Southern Pacific EMD GP-40s. I then thought maybe it was because the train was entering a curve on the layout. I had to increase the throttle to get it back up to speed. I run my trains very slowly and the drop in the power almost made the train stop. After the train left the block (section of track covered by the signal), the engines raced and I had to quickly turn the throttle down.
I started reading up on the problem and finally put my finger on it. The Analog Block Detector was working on my DCC layout, however, the detector it was sopping up power from the track and slowing the train down. It was really starting to bother me more and more. I then tried running one of my 2-8-8-2s with sound in the same block. The engine slowed down and so did the chugging sound. I knew I was not going to be happy with this at all.
After spending a lot of time reading up on this problem, searching the web for hours, visiting model railroading forums for solutions, I found the suggestion to use a DCC block occupancy detector from Digitrax. I really did my homework first and boy I am glad I did. I ran across the Digitrax SE8C which I could use to drive the Atlas signals. You can drive 32 signal heads with this device. I was stopped in my tracks when I saw I had to purchase software to program the SE8C. I gave up on the idea and purchased a BD4 Quad Occupancy Detector. Searching the web on how to wire it to the SCB, I became very frustrated. I could not find any wiring diagrams. I found one for the NEC BD-20 but not the BD4 by Digitrax.
After playing around for about 4 hours I hit on the magic combination, which now seems straight forward, and it works great. At first I could only get the signal to go from green to red to green. The diagram below operates the signal correctly going from green to red to yellow and back to green. I have run into one snag with this setup. For some strange reason, each Atlas Signal Board must be hooked up to a different power source. I uncovered this when I went to hook up a second signal to the same BD4. I just don't think BD4 plays well with the Atlas Signal Board. So unless someone can come up with a solution (a better man then me) this is not going to be very cost effective. Giving up on the Digitrax BD4, I began to explore other options.
Stay tuned to see how I do.
As I said earlier, I found the wiring diagram for driving the Atlas Signal Board with NCE's BD-20. It was a very straight forward wiring. I did the wiring first at my work bench to keep from having to work sitting on the floor and working with my arms over my head for any length of time. I prewired everything so all I had to do was loop the feeder wire from the bus wire to the track through the hole in the current transformer on the BD20. Unlike other detection units the BD-20 requires no direct forward connection to the track. I found that one loop through the current transformer does the trick. Then I hooked the Atlas Signal Board to DC transformer to drive the actual signal head and as well as the LED on the BD-20. I have now hooked up 4 signals and they work like a charm. The BD-20 is so much easier to hook up and less money than the Digitrax BD4. I have included the wiring diagram to the right.
My next project will be attempting integrated operations of 2 signals. To do this I will need to plug in the modular Atlas Model Signal Cable that is appropriate for the block size. The cables are available in lengths of 7’, 15’ and 25' lengths. I will be using the 7 foot cable. One end of the signal cable plugs into J1 connector of the SCB1. The other end will go into J2 of SCB2. Installation of the integrated Signal Cable automatically disengages the timed yellow aspect. All aspects will now be under full control of the blocks and signals in front of and behind the train.
