Thanks for the reply.Do you think I could get away with doing this to just some of the wires within the cable? I presume that some of them are more critical than others for sending the video signal? Any ideas on the minimum number I would need to block to effectively turn off the signal?Thanks.
One alternative is to use an HDMI switcher. You can get these cables for $5-10 from Hong Kong merchants. Here is the cable sold by an Amazon reseller: http://www.amazon.com/SANOXY-Switch-Switcher-Blu-Ray-HD-DVD/dp/B0040G5KY6/ref=sr_1_2?ie=UTF8&qid=1345843556&sr=8-2&keywords=hdmi+switch+boxesI would imagine if you open the box, it should be fairly easy to have the arduino control the switcher by simulating the button press with an opto-isolator.
However, I would be sure to measue the voltage outputed by the switch before connecting it to an Arduino. It appears to not have any dedicated power supply. So the voltage levels are likely whatever the manufacturer considered most convenient to get from the HDMI cables, and that could be something either higher or lower than the 5 VDC from an Arduino pin. At worst that means a bit additional level shifting circuitry, but it's something that should be detemined before connecting the Arduino.
That's the point of using an opto-isolator. That way there is no electrical connection between the arduino and hdmi switch (opto-isolator is a chip with a LED and a photo-sensor inside, the arduino turns on the LED, and then the photo-sensor closes the circuit on the other side when it senses light). If it is high voltage, or A/C, you probably want to use a relay instead of opto-isolator.Otherwise if you connect an Arduino directly to the switch, you need to make sure the grounds are connected, and the voltages are safe, etc.
One thing I did notice about these switches was that they not only switch based on the button, but also if there is only one live input. Presumably they sense the signal somehow. Unfortunately this isn't desirable in my case... As this would bypass my Arduino logic.I might still get one and crack it open... Could still be an option if I can disable the auto switching function.
Re the transistor option... I don't quite understand how this would work. I can see that it provides a switch but don't quite see how I could use this to pass the signal down the cable.
Another option I thought of was using a digital switch.. such as this ... http://www.ebay.com/itm/400312722729?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_1950wt_1095
I could use it to interrupt the data transmission in the cable (seems there are 3 separate data channels in HDMI).
This is a better explanation of the HDMI cablehttp://www.hdmi.org/installers/insidehdmicable.aspx