DNOU8 Instructions

Connecting the Board to your Layout


Each duinoNode requires three power connections:

  • V++, device power from 3.3 – 30 volts
  • Vcc, +5v logic
  • GND, shared ground for both device and logic
Each duinoNode requires logic and device power feeds. Device and logic power can come from the same +5v power supply.

V++ & Vcc can be tied to a single +5v feed from a power supply of suitable capacity. Multiple power supplies are supported but not required.

Tied Grounds

The single most important requirement is that all grounds MUST be tied together. Specifically this means that the microcontroller ground MUST be tied to both logic and device ground.

This usually isn’t a problem IF the entire system is powered from one power supply, or powered using multiple power supplies whose grounds are tied together at the source.

However, when powering the microcontroller via USB or an independent, untied power supply (such as a wall wart), you MUST run a wire from microcontroller GND to GND of all other power supplies in use.

Grounding problems manifest as unpredictable, uncontrollable switching on the boards.

DNOU8 Logic Connections


LOGIC IN: Each duinoNode requires three logic connections at J2: CP (clock), LP (latch) & DI (data in).

LOGIC OUT: Each duinoNode offers three logic connections at J3 for the next downstream node in the group: CP (clock), LP (latch) & DO (data out).

All node-to-node data connections can be made with ordinary 3-wire servo extension cables.


In addition to chaining boards by wire, you can also stack up to 6 DNOU8 boards together to share the power and logic connections. Stacking is enabled by soldering in 6-pin headers (included with the board) and soldering jumpers on each board in the stack.

Locations for Headers and the Solder Jumpers

Successful stacking depends on setting the correct jumpers for each board to so that each board has uniquely assigned input and output pins.

On the board that will be on the bottom of the stack, solder just one jumper to direct output to a pin: we strongly recommend you select pins in numeric order, so solder the data out jumper at header pin 1.

The Bottom Board.

On subsequent boards solder two jumpers: on the data in side, set the jumper for the pin corresponding to data out from below, then select the next pin for sending data up to the next board.

Jumper settings for the second board in the stack.

Following this pattern, you can mount up to 6 boards in a single stack.

A Stack of 2 DNOU8 boards.

Additional Notes about Stacking

  • All devices served by the stack use the same device power source; mixing device power voltages in a stack is not permitted.
  • Connect power to the bottom board only; the power LEDS on the bottom board will light, but the LEDS on the boards above will not light even though the boards will be fully powered.
  • The order of boards and ports is bottom to top, the same as if the boards were connected by wire instead of stacked.
  • To connect to another downstream board or stack, use the DATA OUT terminals on the TOP board of the stack.

Device Connections

The output of duinoNodes is in Common Anode configuration. All switching is on the “sink” or ground side of the circuit via a transistor array. NJ International, among others, wire their model railroad signals, crossings and other devices in common anode configurations. Common anode devices will have a single lead for power and multiple ground leads. Connect anode leads to the V++ terminal, and individual grounds to each port. So long as current limits are not exceeded (500 mA total per board, up to 100% of that can be on any one active port), multiple devices can be connected to a single port.

DNOU1 Device Connections

While logic voltage VCC is always +5v DC, device power can be at a different voltage between 3.3 and 30 volts DC. You can use a single power supply that supports multiple voltages, like a Mean Well RD-125A, or multiple DC power supplies with their grounds tied together.

Connecting LEDS

DNOU8 outputs have 470ohm resistors. If your device voltage is +12v or less, you can safely attach standard LEDs without additional resistors, unless you want to reduce brightness further. Today’s LEDS produce more lumens with less power than ever before. With most LEDS, +5v device power will give good results without requiring more resistors.

Special Wiring Scenarios

Common Cathode Devices

Coming Soon.

Relay Modules

The DNOU8 is compatible with off-the-shelf home automation relay modules, like the one shown below:

A typical 8 port Home Automation relay module; you’ll also find these in 1, 2 and 4 port versions. The relays run on 5 volts, using opto-isolation to prevent current bleed. The primary contacts can handle household current.

For model railroaders, these relay modules are a great way to implement polarity switching for reversing loops, turnout points, stall motor switch machines (like Circuitron Tortoise) and coil-type switch machines (Atlas, Kato, Peco, etc.)

These modules work with all +5v Arduinos, but using one or more DN0U8s you can control all of your relays using just the 3 pin connection required for duinoNodes. In fact, you can mix relay control with lighting and other applications on the same duinoNode chain.

In this duinoNode chain, the relay module is controlled by the first node; the second and third are lighting nodes. DNOU1 boards shown here; the connection protocols are the same for DNOU8 boards,

You will need to fabricate a cable to connect the relay module to other devices. You can use a female pin header of appropriate size, then attach your cable to the exposed ends. From there, connections are straight forward as shown.

This connection cable is fabricated from a 10-postion (.1″ pitch) female pin header with legs bent to a right angle. I used a spare 10 position ribbon cable, soldering one end to the pin header legs. I attached the VCC pin (via red element of ribbon cable) to shared V++. Data pins are connected in order 1 – 8; the ground line is attached to system ground. DNOU1 board shown; use same ports with DNOU8 board.
Relay ground is connected at the main GND terminal.

Next: Using the Software Library