AVS Special Member
Join Date: Feb 2004
Location: Indian River, Ontario, Canada
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I don't think you'll run into a problem with a feedback loop if you use your USB-UIRT for both input and output to your HTPC. I believe the USB-UIRT is 'blind' when it's transmitting.
The circuit you provided probably will work, for a while that is. Based on 12V, the 15 ohm current limiting resistor, and a typical IR LED, the transistor would be supplying around 600mA to the LED. The problem is the 2N3904 transistor is only rated at 200mA. It would be better to substitue a higher current 2N2222, which is rated up to about 600mA.
Likewise, adding additional LEDs in parallel and dropping the value of the current limiting resistor is bad for a number of reasons. If you want to triple the output of this circuit, use individual transitors and current limiting resistors for each LED, or, select a higher current handling transistor and use individual current limiting resistors on the cathodes of each LED.
That being said, I think a single IR LED being driven at 600mA would be more powerful than most remote control emitters, and will probably work fine for your needs.