@CJ-Cassarino Thanks for the reply. I will try your send syntax in my Arduino rules. Also, the reason you don't see the mqtt tag is that I am using a Serial Gateway not a MQTT gateway.

Simply put I am trying to send a message from Openhab to a MySensors sensor via a Serial Gateway.

My environment is Openhab 1.7 running on RPi 3. I have a stock Serial Gateway running on Nano using RF24. I have two sensors DHT and micro switch sending data to the gateway and values are appearing in Openhab fine. For about week now I have been trying to turn the communication around. In Openhab I have configured an Switch Item called Relay. When it changes from Off to On I have a rule to send a command to the Arduino gateway item. However the message never shows up on the sensor. Any advice would be appreciated.

Here is some of the code, config, and logs:

Relay Sensor:

#include <EEPROM.h>
#include <MySigningNone.h>
#include <MyTransportNRF24.h>
#include <MyTransportRFM69.h>
#include <MyHwATMega328.h>
#include <MySensor.h>
#include <SPI.h>

#define RELAY_1  3  // Arduino Digital I/O pin number for first relay (second on pin+1 etc)
#define NUMBER_OF_RELAYS 1 // Total number of attached relays
#define RELAY_ON 1  // GPIO value to write to turn on attached relay
#define RELAY_OFF 0 // GPIO value to write to turn off attached relay

// NRFRF24L01 radio driver (set low transmit power by default) 
MyTransportNRF24 radio(RF24_CE_PIN, RF24_CS_PIN, RF24_PA_LEVEL_GW);  
//MyTransportRFM69 radio;
// Message signing driver (none default)
//MySigningNone signer;
// Select AtMega328 hardware profile
MyHwATMega328 hw;
// Construct MySensors library
MySensor gw(radio, hw);

void setup()  
{   
  //Wipe eprom
  for (int i = 0 ; i < EEPROM.length() ; i++) {
    EEPROM.write(i, 0);
  }
  
  // Initialize library and add callback for incoming messages
  gw.begin(incomingMessage, 105, true);
  // Send the sketch version information to the gateway and Controller
  gw.sendSketchInfo("Relay", "1.0");

  // Fetch relay status
  for (int sensor=1, pin=RELAY_1; sensor<=NUMBER_OF_RELAYS;sensor++, pin++) {
    // Register all sensors to gw (they will be created as child devices)
    gw.present(sensor, S_LIGHT);
    // Then set relay pins in output mode
    pinMode(pin, OUTPUT);   
    // Set relay to last known state (using eeprom storage) 
    digitalWrite(pin, gw.loadState(sensor)?RELAY_ON:RELAY_OFF);
  }
}


void loop() 
{
  // Alway process incoming messages whenever possible
  gw.process();
}

void incomingMessage(const MyMessage &message) {
  Serial.println("message received");

}

arduino items

String Arduino "Arduino" { serial="/dev/ttyUSB0@115200" }

Contact Garage_Door             "Garage Door [MAP(en.map):%s]"          (gGarage, Windows)
Number Temperature_Basement     "Temperature [%.1f F]"  <temperature>   (Temperature, gBasement)
Number Humidity_Basement        "Humidity [%.1f %%]"    <temperature>   (gBasement)

Switch Relay          "Relay"  (gBasement)

test.rules

import org.openhab.core.library.types.*

rule "Send Relay Arduino Command"
when
        Item Relay changed from OFF to ON
then
        logInfo("FILE","Entering Rule: Send Relay Arduino Command")
        sendCommand(Arduino, "105;2;1;0;2;1\n")

end

openhab.log during registration

2016-04-24 11:51:57.728 [INFO ] [org.openhab.model.script.FILE ] - nodeId: 105 childId: 255 msgType: 3 subType: 6 msg: 0
2016-04-24 11:51:57.841 [INFO ] [org.openhab.model.script.FILE ] - Entering rule Arduino sends to Openhab
2016-04-24 11:51:58.229 [INFO ] [org.openhab.model.script.FILE ] - Entering rule Arduino sends to Openhab
2016-04-24 11:51:59.161 [INFO ] [org.openhab.model.script.FILE ] - nodeId: 0 childId: 0 msgType: 3 subType: 9 msg: read: 105-105-0 s=255,c=3,t=12,pt=0,l=3,sg=0:1.0
2016-04-24 11:51:59.454 [INFO ] [org.openhab.model.script.FILE ] - nodeId: 0 childId: 0 msgType: 3 subType: 9 msg: send: 0-0-105-105 s=255,c=3,t=8,pt=1,l=1,sg=0,st=fail:0
2016-04-24 11:52:00.462 [INFO ] [org.openhab.model.script.FILE ] - nodeId: 105 childId: 255 msgType: 3 subType: 12 msg: 1.0

openhab.log after turning on switch

2016-04-24 11:49:30 - Relay received command ON
2016-04-24 11:49:31 - Arduino received command 105;2;1;0;2;1
2016-04-24 11:49:31 - Arduino state updated to 0;0;3;0;9;send: 0-0-105-105 s=2,c=1,t=2,pt=0,l=1,sg=0,st=fail:1

openhab events.log

2016-04-24 11:49:31.056 [INFO ] [org.openhab.model.script.FILE ] - Entering Rule: Send Relay Arduino Command
2016-04-24 11:49:31.522 [INFO ] [org.openhab.model.script.FILE ] - Entering rule Arduino sends to Openhab
2016-04-24 11:49:31.943 [INFO ] [org.openhab.model.script.FILE ] - Entering rule Arduino sends to Openhab
2016-04-24 11:49:32.651 [INFO ] [org.openhab.model.script.FILE ] - nodeId: 105 childId: 2 msgType: 1 subType: 2 msg: 1