Re: Atlas signal - Tortoise Interlocking

Allan AE2V



The Atlas switch machine has a common terminal.  You don’t need to get hung up over the term common.  Just look at the Atlas diagram you sent me.  You will see a blue wire that went to the Atlas.  Instead of connecting that blue to the Atlas, connect it to terminal 4 of the Tortoise.




From: <> On Behalf Of Bill Wilken
Sent: Saturday, September 12, 2020 1:43 PM
Subject: Re: [w4dccqa] Atlas signal - Tortoise Interlocking




Thanks for your help on this.  I have only one follow-up question.  You indicate the "blue" wire should run from Tortoise terminal 4 to common.  But common on what?  A rail?  Common on the Atlas signal control board?  Or common on the BD-20?  




On Wed, 2020-08-05 at 11:29 -0700, wirefordcc wrote:

Hi Bill,

I reviewed the Atlas schematic you supplied and also went the Atlas website to learn a little bit about the Atlas Signal Control Board (SCB).  I found that it does not control the Atlas switch machine or Tortoise as you desire.  Rather, the Atlas switch machine or a Tortoise provides input to it.

The blue wire you see on the Atlas schematic that goes to the common on the Atlas switch machine would be attached to terminal 4 on a Tortoise.  The two green wires shown going to the Atlas switch machine go to terminals 2 and 3 on the Tortoise.  If you get the wrong aspect displayed, swap the wires going to 2 and 3.

You can control the Tortoise with DCC via an accessory decoder like made by NCE or Digitrax or through any traditional means of controlling a Tortoise switch machine. For more on controlling Tortoise switch machines, visit my website at:

Allan Gartner
Wiring for DCC

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