Read the statement by Michael Teeuw here.
Powrering the Raspberry Pi from the tv, possible solution
Hey everybody. If you’re looking for a way to run your Magic Mirror with one power cord, I might have a solution. When I first started working on my first Magic Mirror, I was looking for a TV with a USB port that could power the RasPi, so the finished product would only need one power cord. I’ve read a lot about how the USB ports on most TVs don’t really supply power and so they won’t work for this purpose. Eventually I decided I’d have to figure a different way to get it all to work with just one cord, and would deal with that problem later.
Anyway, I went to a pawn shop to see if they had any cheap flatscreen TVs that I could use for the project, and they had a few of these Sceptre brand TVs for about $30 apiece. I grabbed a good looking 19” widescreen, bought it, and took it home.
Just for the hell of it, I decided to see what would happen if I plugged a RasPi 3 into the USB and HDMI ports. I turned the TV on expecting to be disappointed, but it was not so! The TV turned on and the RasPi booted up! No low power warning at all! I tested it out by playing some games on RetroPie and it worked like a charm.
My buddy came over with his multimeter and we cut an old usb cable in half to see what kind of output the USB port was giving and it was a steady 5.2V and 2.1A! Now that I’ve got the Magic Mirror software up and running, I’ve tested it by leaving it on first over night, and then overnight and all next day while I went to work, and there were no problems!
It doesn’t work with a RasPi 3B+, though. I get the low power warning and it won’t boot. But it works great for the regular 3 and 0.
Hope some of y’all find this useful and helpful!
Interesting approach. What happens, if you put the tv into standby? Is usb turned off then causing the Pi to loose power? Or is the pi still running?
Yes, if the TV goes into standby mode it will cut power to the Pi, but I found a user manual online and was able to turn that off on this particular model. It was somewhere in the TV advanced settings. This TV will stay on indefinitely until it’s turned off or loses power itself.
Since I’m pretty new to programming and coding and the whole concept of single board computers, I’m kind of learning as I go along. So, I decided to just keep it simple and having the Pi and TV “always on” seemed like simplest way I thought of doing this. (I do have the Pi set to reboot every Monday at midnight.) I know there’s a better way to do this, I’m just not there yet.
Well. You could add a battery pack to the pi, react on the “power loss” and shut the pi down correctly. On the other hand, it should not consume too much energy at all.
Just make sure power is not simply cut off or your file system at some point might become corrupted
Oh that’s a great idea to use a battery for that! Thanks!