Hello all,
I think about replacing my optical cable that runs over whole room with IR transmission. Has anyone tried it? I think it should be easy with existing circuits: SPDIF to TTL converter, TTL to IR converter, IR to TTL converter, TTL to SPDIF (COAX) converter. It all should exist, right? Some wireless headsets use IR as well (but not that I want, I guess they use lower carrier frequency)
Thanks, Jan
I think about replacing my optical cable that runs over whole room with IR transmission. Has anyone tried it? I think it should be easy with existing circuits: SPDIF to TTL converter, TTL to IR converter, IR to TTL converter, TTL to SPDIF (COAX) converter. It all should exist, right? Some wireless headsets use IR as well (but not that I want, I guess they use lower carrier frequency)
Thanks, Jan
Infrared transmitters and receivers meant for remote control signals usually work with very low bitrate signals modulated on a 38 kHz carrier that on/off modulates the infrared light. Those are unusable because they can't handle the required bitrates.
Directly modulating an infrared LED with the S/PDIF bit stream is possible, but you then need a wideband receiver. The receiver should block DC, otherwise any infrared light falling on it will block the transmission. You can also have interference from lamps. For example, an incandescent lamp running on 50 Hz AC will produce infrared with a 100 Hz ripple in its amplitude.
When someone stands in the ray, the audio will drop out, probably with a loud thump.
Directly modulating an infrared LED with the S/PDIF bit stream is possible, but you then need a wideband receiver. The receiver should block DC, otherwise any infrared light falling on it will block the transmission. You can also have interference from lamps. For example, an incandescent lamp running on 50 Hz AC will produce infrared with a 100 Hz ripple in its amplitude.
When someone stands in the ray, the audio will drop out, probably with a loud thump.
Well, TOSLINK is IR .
Anyway, it should be possible. You would need a local clock, have a large buffer , and code to do dropouts gracefully. The line of sight may not be as big a problem depending on the environment due to reflectivity. CFLs are far worse than the incandescent.
You would want to put it on a carrier.
Bottom line, if you really need to be cable-less, then BT is already developed for that.
Anyway, it should be possible. You would need a local clock, have a large buffer , and code to do dropouts gracefully. The line of sight may not be as big a problem depending on the environment due to reflectivity. CFLs are far worse than the incandescent.
You would want to put it on a carrier.
Bottom line, if you really need to be cable-less, then BT is already developed for that.
I have read web pages from people who have used an LED or even a laser to successfully carry SPDIF thru free space. See for example:
https://www.jensign.com/SPDIFLink/https://www.diyaudio.com/community/threads/thoroughly-affordable-wireless-toslink.289198/
Maybe these will serve as some inspiration for your project.
https://www.jensign.com/SPDIFLink/https://www.diyaudio.com/community/threads/thoroughly-affordable-wireless-toslink.289198/
Maybe these will serve as some inspiration for your project.
I wonder why the author of your first link chose DC coupling between the transimpedance amplifier and the voltage amplifier.
You'd need very high power to do this - bandwidth of optical sensors depends on the intensity of light falling on the photodiode, which drops according to inverse-square of distance. A 5mm-square photodiode 4m away gets a signal 66dB down from an emitter with a half-sphere radiation pattern. You'd need to have very good optical filters to keep visible light from the sensor when the received IR is low intensity.
An optical fibre loss is much less than this and screens out optical interference completely.
The good news is you can get IR LED arrays of 30W or more - but I have no idea what bandwidth they have.
The first reference of CharlieLaub (post #6) uses an ordinary small LED at the transmitting side and a photodiode and a 40 mm-diameter plastic lens at the receiving side. Apparently that's enough for a distance of 3.2 m.
Jan probably needs more or better lenses or a more powerful transmitter for "replacing my optical cable that runs over whole room", unless the room is quite small.