Isolated Input Board

$12.95 Contact Us to Order

The QuadLN_S Isolated Input Board allows a MAIN IO or AUX IO port to provide 4 optoisolated input channels for interfacing with output signals from DCC-powered devices or from other devices using a different power supply ground than the QuadLN_S. The board can be plugged into either the Main or Aux IO port on the QuadLN_S. The built-in isolation helps prevent ground loops and sneak paths that can occur when connecting to signals that are not referenced to the same Ground potential as the QuadLN_S.

One typical use might be to collect the state of DCC circuit breakers. Circuit Breakers are typically powered by the DCC signal itself and any output status signals would likely not be referenced to the QuadLN_S Ground. By using the Isolated Input Board the circuit breaker status can be safely monitored and reported via Loconet, used to drive indicators around the layout or shown on a control panel in JMRI.

The required input current is just a few milliamps. Input current must be kept under 15 mA in all cases. Each channel has two 470 ohm input resistors to help limit the input current. One resistor is inserted in series with the input by default. This is sufficient when connecting to an LED output or other signal of 5 volts or less.

For high voltage signals up to 12 volts or so, a second 470 ohm series resistor can be added by cutting a trace on the bottom of the board. For higher voltages you must add a suitable series resistor to limit the current.

If the external output already limits current to a few milliamps, a solder jumper is provided on the bottom of the board so that the onboard resistor can be easily bypassed. Don’t do this unless you are sure.


  • Plugs into a QuadLN_S MAIN or AUX IO Port
  • Provides 4 independent Isolated Inputs
  • Low input current requirement, similar to driving an LED
  • Includes mounting screws and standoffs
  • The Isolated Input Board instruction sheet has the details (coming soon)

Isolated Input Board Instruction Sheet

The instruction sheet for the Isolated Input Board will be available soon.