Dear all

I could figure out what are the codes that I need to send to turn on and off the projector and was able to reset the lamp with my Arduino circuit. Here is how you have to do it:

1. Download and install the Arduino software
    
2. Download and install the Multi-Protocol Infrared Remote Library. Just download the files and copy the folder "IRremote" inside the "libraries" folder of your Arduino installation directory.
    
3. Setup your Arduino board as shown here. You only need One IR diode and a resistance (I didn't have to use the resistance, but you may need it). You don't need the receiver circuit.
    
4. Open Arduino and put this code on it:
   #include
   #include
   IRsend irsend;
   void setup()
   {
     Serial.begin(9600);
   }
   void loop() {
     if (Serial.read() != -1) {
         Serial.println("Begin Sending");
         time_t t1 = now();
         for (int i = 0; i < 150; i++)
         {
             irsend.sendNEC(0x189710EF, 32); //ON
         }
         time_t t2 = now();
         Serial.println("End Sending");
         Serial.print("Running time: ");
         Serial.print(t2 - t1);
       }
   }
    
5. Upload the code to your Arduino, then start the "Serial Monitor" and send some character, ie: '1'. It doesn't matter what you send, the software will start sending the signal several times. If the final input you see is: "Running time: 12", then you are done. If not, modify the value of the upper limit of the variable "i" till you get a running time superior to "10", ie: put "i<200". In order to see if the LED is sending something, take a digital camera (the one on a smart phone will work) and point it to it. If you see a blinking white light, then the LED is sending.
    
6. Point the IR LED from your circuit to the Infrared receiver on the Plus projector.
    
7. Turn on the projector by pressing the red "POWER" button.
    
8. Press the "MENU" button, then enter to the "POWER MENU" and highlight "LAMP USAGE".
    
9. Begin sending the signal from your Arduino.

That's it. You will see "LAMP USAGE: 0"

Anyway, for the interested in knowing how to get the codes, here it is:

First at all, I used the codes posted by 3FG: File - Plus U2 Series Projectors

Then, I tried different combinations of the “on” function (Decimal: 8) as pointed by 3FG. It turns that the custom code is: 1897, which is 18E9 but from right to left, then reversed. So the original binary is:
0001 1000 1110 1001 = 18E9
Then from right to left we get:
1001 0111 0001 1000 = 9718
Then we invert the order of the hexadecimal number and it gave us: 1897

Then to get the function code of the on function (Decimal: 8), we mixed its hexadecimal code with its complement like this: 08F7, then we reversed it as follows:
Original binary: 0000 1000 1111 0111 = 08F7
From right to left: 1110 1111 0001 0000 = EF10

Finally we invert that number and we get the function code: 10EF

So the code we need for the arduino is: irsend.sendNEC(0x189710EF, 32);

Thanks to DrNeon for giving me the idea of the Arduino board and to 3FG for its helpful post.

I also want to thank Mr. "Technical Support" :-) from the Plus company for his help.

Best regards
Josef