CML Electronics by GFB Designs

DCC and LocoNet Accessories

SIGM20 Colour Light Signal Controller

The SIGM20 is an automatic colour light signal controller for your model railway. It  sets the signal state for up to 8 signals automatically according to the state of the trackwork (e.g. points), other signals and block occupancy detectors. It does this automatically, without any other computers involved: so no PC is required to operate the railway. The board can control simple blocks, simple and complex junctions ....automatically.


Signals are controlled automatically as trains move around the railway. Signals can be programmed so that for example:

  • If the track ahead is occupied by another train, the signal will go red;
  • If a point is set against the track, so that it would not be safe to proceed, the signal goes red;
  • That can be extended to set the signal through complex junctions;
  • The logic for 3 and 4 aspect signals is followed: if the next signal is red, this signal will go amber and so on.



The SIGM20 drives LED signals directly. Via optional adapters it drives incandescent lamp signals or semaphore signals controlled by Tortoise point motors.

There are a lot of settings available to select how signals operate. We provide a PC program "Locoanalyse" that will allow the settings to be entered in a user friendly manner, and be saved to a file on the PC. The settings can be programmed onto the SIGM20 through LocoNet. The PC is not needed thereafter.

How it Works

The SIGM20 operates as a loconet device in the same way a throttle does. Through LocoNet, the SIGM20 is able to sense the states of points & sensors and can decode the DCC accessory commands that go to accessory decoders. The SIGM20 generates LocoNet messages when signals change states so that other devices can "know" the state of any other signal.

Points don't need to have feedback microswitches on their tiebars: see here for details.

Other Information

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Frequently Asked Questions

How To use the SIGM20...