FAQ: How does the SIGM20 know the state of the points?

Some accessory decoders have a LocoNet interface (e.g. DAC20, DS54). These are able to report the point positions after power up. This is done using both "Output State" and "Turnout Feedback" messages. Both DAC20 and DS54 generate "Output State" messages to report the memorised point position. Both generate "Turnout Feedback" messages if feedback switches driven by the tiebar are connected. (Unfortunately, the DS54 does not encode the "Output State" messages properly if solenoid type point motors are attached).

Thereafter, the SIGM20 will detect any changes of the point state by monitoring any LocoNet feedback packets, and the DCC commands on the rails to change them. So when a throttle is used to change a point, the DCC command to the accessory decoder will be seen by the SIGM20 and it will "know" the correct state. If the SIGM20 has detected that turnout feedback messages are being used by that point, it will use them instead.

So what this means is:

  • If you use DAC20 accessory decoders, with or without "turnout feedback" microswitches, then the SIGM20 will always "know" the states of the points.
  • If you use DS54 decoders with turnout feedback microswitches, the SIGM20 will always "know" the states of the points.
  • If you use DS54 decoders with solenoid point motors but no turnout feedback reporting, the SIGM20 will only "know" the state of the point after it has been operated for the first time.
  • If you use accessory decoders without LocoNet interface, the SIGM20 will only "know" point position after they have been operated for the first time.

Many people will be in the latter position - no feedback reporting connected. It isn't the end of the world: there are at least four ways to proceed without adding any microswitches:

  • If you are using a PC control application (e.g. RR&Co), arrange for it to reset all points to a known state when the program starts up.
  • If you are using a DTM30 Tower Master to control points, use the "initialise" function to drive all points to an initial state.
  • Use a handheld throttle to drive points to an initial state.
  • Use a DSC100 route to set points to an initial state.