Sharing one monitor

[sadarahu]

I have 3 devices: Rasberry Pi2, Rasberry Pi3 and Rasberry Pi-Zero.
Ras3 has Ubuntu installed, the other 2 standard Rasbian.
I'm trying to connect all of them to HDMI switch but I'm having lots of issues. Fist switch was simple 3-in 1-out.
When I'm connecting the OS goes to 640-480 mode which looks terrible (to big).
I thought initially it is a switch problem so I bought more expensive and sophisticated one. Same thing happens. Now not only resolution goes to 640x480 but also no signal is found. I have to unplug and plug back the HDMI cable to the switch to make the signal go to the monitor. This 3nd switch was highly rated on Amazon although I haven't seen anybody using it with RasPi.

Any suggestions ? I'm thinking about hard coding the screen resolutions into the OS but I'm not sure if this is possible and if this is the best route to go. I do not understand why when booting up the device does not recognize it is connected to HD monitor, although when connected directly it all works fine.
Any suggestions ?

ARTHUR

[Aydan]

I have 3 devices: Rasberry Pi2, Rasberry Pi3 and Rasberry Pi-Zero.
Ras3 has Ubuntu installed, the other 2 standard Rasbian.
I'm trying to connect all of them to HDMI switch but I'm having lots of issues. Fist switch was simple 3-in 1-out.
When I'm connecting the OS goes to 640-480 mode which looks terrible (to big).
I thought initially it is a switch problem so I bought more expensive and sophisticated one. Same thing happens. Now not only resolution goes to 640x480 but also no signal is found. I have to unplug and plug back the HDMI cable to the switch to make the signal go to the monitor. This 3nd switch was highly rated on Amazon although I haven't seen anybody using it with RasPi.

Any suggestions ? I'm thinking about hard coding the screen resolutions into the OS but I'm not sure if this is possible and if this is the best route to go. I do not understand why when booting up the device does not recognize it is connected to HD monitor, although when connected directly it all works fine.
Any suggestions ?

ARTHUR

Your problem seems to be that the hdmi switch does not route EDID to inactive inputs, so the raspberry can't read the monitor information and select the proper resolution. One way to circumvent this is to either dump the edid data with the tvservice command and add a force_edid line to config.txt, or force set hdmi_group and hdmi_mode in config.txt

Regards
Aydan