Today I stumbled upon the WDLabs Media Stick for the Raspberry Pi Compute Module at the ModMyPi Online Store and was immediately reminded of the Intel Compute Sticks or the ASUS Stick PCs.
But the WDLabs Media Stick doesn't seem to be powered over HDMI as it still needs a 5V input over a Micro-USB socket according to the (very short) PDF manual.
So I wonder: Is it possible with some intermediate board to power a Raspberry Pi Zero or a Raspberry Pi Compute Module from the HDMI port of a TV? (I imagine this intermediate board to be similar to those Power-over-Ethernet adapters you can get for the normal Raspberry Pi.)
There is an rather old thread on this topic on the Raspberry Pi forums which says it's impossible. But given some of the comments in there about e.g. the MHL standard and the fact that the Raspberry Pi Zero didn't exist back then, I expect that most information in that thread is outdated. Also the claim that HDMI sinks can only provide about 50mA (which is about the amount of power two keyboard LEDs consume) seems to invalidated by the pure existence of the Intel Compute Stick. But another not so old thread on Quora comes to the same conclusion: HDMI only offers 50mA.
Or is maybe my assumption wrong that the Intel Compute Stick and similar devices are powered over the HDMI port? Because they're usually advertised as "just plug it into an HDMI TV or monitor and start working" which suggests that no additional power supply is necessary.
Then again, MHL seems to provide between 500mA (MHL 1) to 2A (MHL 3) over an HDMI connector.
So in theory it should be possible to power even an Raspberry Pi 2 over an MHL connector if there's an intermediate board which takes care that both HDMI signal and power are connected to the correct sockets or GPIO pins on the Raspberry Pi.
Anyone already did something like that? Or is there already a ready to use board/HAT/pHAT for that? Actually the ZeroStem follows a similar idea, just with USB instead of HDMI, i.e. making a USB stick out of the Raspberry Pi Zero.
At least the thought of having a Rasperry Pi Zero W with a Bluetooth keyboard and mouse which just connects to the MHL-enabled HDMI port (and really nothing else ;-) of a TV to start working sounds like a really nice setup.