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Reverser Picture
This is my prototype reverser in my (very) short 'loop'.  The arrows indicate cuts in the tracks.  The circuit board contains: yellow brick (dual latching relay), 4 signal diodes (top right), 4 rectifier diodes (above and below the relay), two snubber diodes cross the colis of the relay, two transistors (just to the right of the relay), three resistors, and three capacitors.
Schematic
This is the schematic of the dual latching relay reverser.  The four diodes on the left rectify the DCC to make +12V.  This drives the relay through a (optional) resistor to limit current (in this case I am using a 5V relay).  Two diodes from each isolated section of rail carry positive DCC pulses to the transistors, turning on the appropriate latching coil.  The DPDT relay contacts are wired to reverse the incoming DCC.   Note the two snubber diodes across the relay coils.
Parts:
  • Aromat DS2E-ML2-DC5V (Digikey 255-1074-ND) or DS2E-ML2-DC5V (Digikey 255-1075-ND)
  • 6 x 1N4004
  • 2 x 1N4148
  • 2 x 2N2222
  • 2 x 1uF
  • 1 x 100uF
  • 1x82 ohms (not needed for the a 12V relay)

  • 2x4k7
This shows an example of the reversing section in a simple layout.  Normally, the reversing section should be long enough to hold an entire train length.

By the way, this circuit works for DC engines, but as they try to exit, they reverse direction (and reversing again at the opposite end).  To get them to exit, you have to manually reverse their direction a second time just after the first reverse.  This isn't very prototypical - a little hiccough on the way out.

As a bonus, because of this side effect, this circuit would also make a good reversing circuit, for say a diorama, in which you wanted an DC engine to shunt back and forth.