Hola Jose, Serial.println and Serial.write are Arduino functions and not from mathematica.

For Serial.println > http://arduino.cc/en/Serial/Println

For Serial.write > http://arduino.cc/en/Serial/Write

@Fahim Chandurwala, thank you very much. It worked!!

I hope our friends from Wolfram update the documentation. There was no way that I would have figured that out without your help.

Now this works. Using the Arduino Sketch mentioned above.

DeviceOpen["Serial", {"\\.\COM10", "BaudRate" -> 9600}]
readSensor[connection_, type_] := 
     Module[{}, DeviceWrite[connection, type]; Pause[.1]; 
     FromCharacterCode[DeviceReadBuffer[conn]]]
(*Read Temperature*)
readSensor[conn,"T"]
(*31.00000*)
(*Read Humidity*)
readSensor[conn,"H")
(*42.00000*)

@Diego Try "\\.\COM10" instead of "COM10" as a workaround.

DeviceOpen["Serial", {"\\.\COM10", "BaudRate" -> 9600}]

Hola Jose,

Indeed I closed the Serial Monitor and Putty. Only one program can communicate with the arduino at a time. The reason Im showing it on the screen is that indeed the COM10 port works with all tools except mathematica.

Here is the sketch

#include <dht11.h>
dht11 DHT11;
#define DHT11PIN 2
int inByte = 0;         // incoming serial byte
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
 if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    if (inByte == 84){
      int chk = DHT11.read(DHT11PIN);
      Serial.println((float)DHT11.temperature, DEC);
    }
    if (inByte == 72){
      int chk = DHT11.read(DHT11PIN);
      Serial.println((float)DHT11.humidity, DEC);
    }

 }


}