This page has been written to answer the questions we get asked about using our units on a DCC controlled model railway.
The vast majority of our boards are independent of the control system, in other words they work with DC (analogue) DCC and even clockwork because it is the movement and position of the trains which activate the units. Ideally it is simpler to use a totally separate power supply and keep the two systems separate. This has several advantages.
However sometimes it is inconvenient to run wires long distances from a separate supply and modellers would like to power a unit directly from the DCC on the track For example you may wish to power an IRDOT-P to switch a point at a reverse loop automatically.
If you wish to use the DCC track for power we recommend using a bridge rectifier. This will change the DCC track voltage to a DC voltage within the tolerance of our units. Bridge rectifiers are inexpensive and simple to use.
We are often asked about how to control our units with DCC for example you may wish to open and close level crossing gates or overide MAS-Sequencer controlled signals to red or operate bouncing semaphore signals with a DCC controller.
The simplest and safest way to do this is to use a DCC decoder set up for operating slow motion point motors and wire this to operate the coil of a relay. The DCC decoder moves slow motion point motors by changing the polarity. A relay coil would be energised regardless of the polarity of its coil. This is the reason for using the diode. For one polarity the diode will conduct and for the other it will not, hence the relay will switch on and off.
The the relay contacts are wired to the board you wish to operate, as the relay contacts are completely isolated there is no electrical connection between the DCC supply and the Heathcote units. This provides good protection from short circuits etc. In the example they are shown wired to operate one of the S (start) terminals of a Dual Servo Controller.
If you have several units that are connected to one another (for example a MAS-Sequencer and IRDASC-4 you should power them both from the same bridge rectifier.
This diagram shows the same thing less symbolically. The red dots represent the 6 pins of our 12 volt 3 amp relay. The Dual Servo controller can either be powered from a seperate 12 volts DC power supply or from the DCC track voltage as described previously. The 2 pins connected by the green wires are the connections to the relay coil.