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Model Railroad Control Systems

Approach Indicator Controller


Approach Indicator Controller

0.20 LBS
Calculated at checkout

Product Description

The Approach Indicator board alerts a train order operator that a train is on approach (“on the bell”) and that he should contact the Dispatcher to determine if there are additional orders for the train. It can handle up to 4 stations, 2 with 4 photo transistors (home and distant for East and West) and 2 more with a logic output from a detector such as our Enhanced Optical Position Detector. The sensors are paired in each approach direction so that unwanted “dinging” does not occur when a train leaves the station.


  • Supports one or two stations with internal conditioning of photo transistor signals
  • Supports an additional one or two stations with digital inputs from detector assemblies
  • All connections including +5 and ground are brought to 0.100 connectors
  • A 2.1mm barrel jack is provided if you choose to supply power from a 5V wall wart.
  • All components use through-hole technology for ease of assembly and repair.
  • Logic level outputs are provided for each station, as well as isolated “dry contacts” on relays. The relays are rated at 1A @ 48VDC.
  • The relay outputs can optionally connect to ground by use of onboard jumpers
  • Each output has an associated LED which is helpful in debugging, when relays are equipped

The Approach Indicator may be ordered equipped for one or two circuits with analog sensors (4 for each circuit), or 4 circuits: 2 analog and 2 more digital, where you must supply detectors for the digital inputs.  We also offer "SoundBytes" sound modules with authentic US&S bell sounds from Iowa Scaled Engineering.  *Note we use "commodity" Arduinos from various sources, you may order the Approach Indicator Controller without  a Nano and provide and program your own!

Approach Indicator Assembly and Installation Instructions (includes schematic, board layout and Bill of Materials)


Board Layout

EAGLE CAD Files (sch + brd)

Gerber Files for PC Board Production

Source Code for Arduino Sketch

Source Code for Barry Draper's alternate sketch used at La Mesa Model Railroad Club ("Tehachapi")

Source Code for "ResistTest" sketch

More documentation on the Arduino sketch can be found on Jon Schmidt's website:



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