Reply to "An Arduino-based DCC Turnout Controller"

Here are a couple pics I took of the two different non-derail setups. Most of the switches use a contact sensor arrangement, similar in principle to the Lionel 022 switches. For this setup, the short main and short curved rails are isolated from the track ground and are instead each wired to an A/C optocoupler on the controller. When a wheelset rolls onto the short rails, it closes the circuit to the track ground on the outer main rails. This causes the opto output to go low, signaling to the controller that there is a train present.

The advantages of this arrangement (vs. the optical sensor) are cost and ease of installation. The main disadvantage is that the short rails are isolated from track ground and cannot carry any usable current for engines (although they are so short this is not really an issue in practice). They also require the use of insulating pins on each short rail.

Here is a #4 turnout wired with the contact sensors:

I use the optical sensors on the longer turnouts and the double crossover, where I want all the rails grounded to minimize the chances of engines stalling. The sensor is a self-contained unit consisting of an IR emitter, IR detector, and logic circuitry. When a train passes over the sensor, the detector picks up the reflected IR from the underside of the train, and the output of the detector circuit goes low, signalling to the controller that a train is present. Each turnout needs two sensors. They are more involved to install than the contact sensor wires, because each sensor requires a power, ground, and signal line. However, the installation is pretty tidy, and they provide the best possible track continuity.

Here is a #230 curved turnout equipped with the optical sensors. You can also see the ground wire I added for the short rails, which are not grounded by default.