HDMI Switch - Page 1
Forum section: electronics / beginners

author: Kaluriel
author_rank: Contributor
timestamp: March 12, 2013, 02:22:45 am
content: A few year ago I decided to upgrade to optical audio for my PS3 and Xbox to get more audio channels, so I bought a HDMI switch. It is a 4 input HDMI switch that also switches optical, and it had a remote control.However recently it is on the blink, the AppleTV video keeps going off. And worse, the WiiU doesn't have a separate optical output, it goes through HDMI which is a problem since there is no way for me to get audio out from the monitor. Plus I wouldn't mind a 5th input for my RaspberryPi and potentially more inputs if I get anything else new.So I thought, why not build my own.- Driving the whole circuit will be a PIC controller, taking infrared input, as well as switches on the box itself.- For the HDMI switching, I was thinking of using an driver IC I had found on Farnell. It is three ports, two of which I plan to use, and the third taking the output from another module so I can chain them together to get more inputs.http://uk.farnell.com/texas-instruments/tmds361bpag/ic-switch-hmdi-3-port-64tqfp/dp/1854445MPKG?Ntt=1854445MPKG- For the optical audio, I thought about just converting it to a digital signal and then switching it using a FPGA, then outputting it back out again as optical.- I wouldn't mind a screensaver mode for when none of the inputs are doing anything. Currently when there is no signal, a bit lime green box is put on the center of the monitor, but I'd prefer something less bright. I don't know if my monitor responds to HDMI commands, I may be able to send a signal to turn it off via CEC, otherwise I'll just generate graphical noise and convert to HDMI.The tricky problem is the WiiU with its audio being sent through the HDMI. To combat this, and the future possibility of other devices not having an optical out, I was thinking of a physical switch to choose between optical input and extracting audio from hdmi input for each port. I chose physical since its not going to change often, only when the device is plugged in initially. I have read that HDMI can have copy protection, however from what I've managed to google, the WiiU doesn't use this.So I was thinking about using a chip such ashttp://uk.farnell.com/analog-devices/adv7611bswz-p/rx-hdmi-low-power-165mhz-64lqfp/dp/1903660?Ntt=1903660to separate out audio, and I will probably need something to split the signal without dividing the power.Opinions on how I'm going about this are appreciated.

author: m0r
author_rank: Newbie
timestamp: March 13, 2013, 01:02:29 pm
content: So in essence you want to build something like this.http://www.amazon.co.uk/Leicke-KanaaN-Matrix-Output-Splitter/dp/B004MYUCF8/ref=sr_1_1?ie=UTF8&qid=1363180368&sr=8-1You can find some Info on a similar device here.http://debugmo.de/2010/01/whats-inside-part-ii-hdmi-audio-splitter/The optical transmission already is digital (https://en.wikipedia.org/wiki/S/PDIF) so there wouldn't be a need to convert it, just pass/switch it through.Have you considered the whole lip sync issue? You'd most likely need a way to delay the audio stream, to sync the video and audio output. To my knowledge auto lip-syncing is done via CEC, which in return is ethernet based. Oh, and have I mentioned it's a buggy piece of shit?Extracting the audio stream from HDMI isn't easy as I'd imagine, because the S/PDIF Bandwith is quite limited you'll need a way to re-encode high-bandwith audio streams to AC3, unless of course your device (the Wii U) just puts out a low bandwith stream compatible with your decoder.*Then again, as you already mentioned, you could run into encryption issues (HDCP). As far as I know bluray players and encrypted TV channels are required to output an encrypted signal to receive certification, so most of them are probably doing it (kicking the consumers ass with non-functioning HCDP crap).It's a very interesting project, but seeing how miserably some (consumer) manufacturers still fail with getting HDMI, let alone audo/video sync properly done I'd truly think about it and google a lot. I don't know about your skills, money and time on hand, but besides passive, signal-transparent switching this could become very difficult in no time. It would be very interesting to read some thoughts from experienced engineers.*I must have overread the text about the ADV7611.

author: Kaluriel
author_rank: Contributor
timestamp: March 13, 2013, 03:46:46 pm
content: Sorry I badly worded the digitising of the audio, I meant converting it to an electrical signal rather than light, splitting light digitally can be awkward. Plus I can then add a buffer to adjust for latency caused by the switching and splitting, before converting it back to light.The link you give is almost what I'm hoping to achieve, only without the splitting, and optional optical input for each HDMI.

author: shamanjoe
author_rank: Contributor
timestamp: March 13, 2013, 08:11:57 pm
content: I'm very excited to follow along on this. It would come in handy if I could build something like it as well. One question though, have you gotten the physical optical audio jacks yet? I have one on my surround sound where the little plastic flip cover is buggered, and I was wondering if I have to replace the whole jack, or just the cover, and I haven't been able to find a good picture of one to see. Thanks.