Re: Atlas signal - Tortoise Interlocking

Bill Wilken


Many thanks.  Actually, I do want the switch machine to provide input ... exactly as you suggest.

On a number of schematics I've seen showing Tortoises connected to signals, the schematic shows a resistor between the signal and Tortoise.  But given that the Atlas signal control board can handle up to 12 volts, I'm guessing that shouldn't be an issue.

I'm all set on switch motor wiring.  Thank heaven for the availability of SMAILs.  The small added charge for the DCC control chip on the switch motor is worth every penny.  

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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