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A number of Asrock boards come with a 4 pin header labelled 'CIR'. The manual includes diagrams showing how to connect a special receiver using a front panel USB connector, but most boards do not come with the receiver or remote.
Since the device looked more than just an IR receiver, I had left those alone in the past, expecting they required that particular device to work correctly. However, I have recently purchased an Asrock Z68M-ITX/HT board which does come with a receiver.
Installing it doesn't show anything on lsusb on linux, and there is no new device detected under Windows because it isn't USB. Inside are two standard 3 pin IR receivers, another sideways one and two SOT23 chips.
One very useful part of this is BIOS support of power on by CIR, so with the adapter in place and the BIOS option 'Power On By CIR' enabled, you can switch on the PC using the remote. Nice.
As good as it is, my main issue is that it isn't really convenient to have it hanging out of the front USB port.
So I thought I'd see how it worked wired direct to a standard TSOP4838 receiver. I wired one up using an old CDROM audio cable, with the ends de-pinned and rearranged appropriately.
1 - 5V (this should be at the same end as the red wires on the USB connector)
2 - IR RX (this is the active high output from the IR receiver)
3 - IR TX (this is not connected, but I presume this is for an IR transmitter?)
4 - 0V (this should be at the same end as the black wires on the USB connector)