Thanks to linux_works from the Adafruit forums for sharing this project!
I’m using the adafruit xbee adapter, a DIY arduino (328 chip), 74125 (to control tx/rx on arduino; software download time puts the xbee on high-z tristate; once arduino boots it enables the 125 chip and the xbee is now clamped onto tx/rx, getting prio (using the 1k resistor trick, too).
my remote (also using xbee and arduino) sends port-change commands over RF to the green board, here, and that uses IR.h to make the modified hdmi switch think its real IR remote commanded a port-change 😉 I have an ir sender led, series R and opto link tube (read: heatshrink tubing) inside the hdmi switch. those switches are in the $10 range and are very common now. they even allow remote IR-in in case you didn’t want to hack the switch itself. the key is to learn the IR codes using the Ken IR.h lib, save them in prog mem and use them on send to trigger hdmi input port changes.
works great. plus, you can save values in eeprom so next power-up, the arduino puts the port back in its last-set state. and, you can query the switch to find out its current port; something that one-way IR can’t ever do!