Seeing nothing on HDMI with 7" screen connected (how do I switch to HDMI?)

[donrecardo]

Hi
I have a Pi 3 with 7" touch screen . It works fine ( thankfully ). and I can use it on the touch screen
without issues
If I plug the tv hdmi cable into the Pi then across the bottom of the TV it shows its recognised it
and displays HDMI 2 RaspberryPi 1080P
but apart from that the screen is black , nothing is shown, no boot sequence , no desktop ,although the touch
screen is still displaying and working fine.
Now if I take out the ribbon cable from the Pi to the touch screen . The TV on HDMI shows everything
from the Pi as it should .I see everything scroll past as it boots up and then the desktop comes up and works fine

I cant keep taking off the touch screen cable every time I want to see it on the TV
surely there must be a way of choosing which screen ( HDMI or Touch Screen) that is active

Hope someone can help

[DougieLawson]

Disconnecting power to the 7" screen is the only way to get HDMI working with the stock standard, non-alpha firmware.

There is some support in the alpha pieces with vc4-fkms-v3d.dtbo or vc4-kms-v3d.dtbo (there's an option to enable that stuff in sudo raspi-config). Running the alpha video code may cause other things to randomly break (that's why it's alpha).

[donrecardo]

Well thanks for replying even though as a noob
most of it went over my head , but I did understand with
the software I am using , it aint gonna happen so I think
my easiest way around it will be use my Pi 3 with the touch screen
and my Pi 2 with HDMI

Cheers
Don

[procount]

By default, the touchscreen has priority at boot time, but you can force the HDMI to be used in preference using appropriate config.txt settings.
You can only switch at boot time.

I have a solution in PINN that reverses the normal priority, so it will normally use the touchscreen, but if you have a HDMI monitor attached at boot, it will use that instead. But you need to install PINN first on a blank SD card, and use it to install your other Operating System(s).

See https://github.com/procount/pinn/blob/m ... igurations

You might be able to adapt this technique to a a normal Raspbian install without PINN, (there might be a forum post about it... can't remember) but in any case, it will potentially require a double boot when you turn it on, so it's a bit slower to start up.