IrDA
19 points by binjip978
19 points by binjip978
You can also take an old 10Mbps NIC, connect it to a makeshift transceiver to get Ronja. Build two and connect your whole apartment building to a growing community ISP. Comes both in Red and IR versions.
Sadly they've stopped in 2006 or so. I think 2.4GHz and 5GHz point-to-point was cheaper and worked better.
Modulated light is fun, though. IR is ideal for introducing kids to invisible communications. Lesson one: blink your TV remote into your phone's camera to make it visible. Lesson two: build a simple IR phototransistor circuit and look at the pulse train using an ADC or oscilloscope. Lesson three: build a TV-b-gone.
Koruza is a much more modern open-source FSO option: https://github.com/IRNAS/KORUZA
Unfortunately it is mostly developed by a company with a commercial version, so they haven't invested much in ease of use for the open source materials. Still, I'd like to try it out some time. Koruza is also intended for shorter-range applications than Ronja was, Koruza states gigabit at 100m typical. For km+ ranges and faster than 10Mbps, I don't know of options outside of the costly commercial vendors (Mitsubishi, MRV).
Newton was supposed to have "diffuse" IR communications, too, sort of a room multicast setup. The Cadillac prototype even had a window on top to receive these sorts of broadcast transmissions but my contact who was on the Newton team says they never got the bugs worked out. Lots of interference problems, as you might imagine.
Meanwhile, my fondest memory of Brad Templeton was him IR beaming a contact to my Palm m505 that said, "You Have Been Hacked."