You can use an android device such as a phone or tablet as a screen for the Raspberry Pi, using a couple of plugins. The RasPi will need a keyboard and mouse plugged in, at least at first and must have SSH enabled and a known IP Address. The RasPi and the 'droid device will both need to be connected to the same wireless network.
There are a few ways to do this - all free - including Microsoft's Remote Desktop Protocol app and the VNC app (Virtual Network Computing). I've been using VNC for many years but for this application at least, it's a bit shite. Much as I hate to bring anything Microsoft into our 'Nix meanderings, their RDP option wins over for quality and performance (there are other RDP apps).
On the Google Play Store install RDP for Android. Then install RDP on the RasPi..
sudo apt update
sudo apt install xrdp
Then on the Android device, click on the RDP icon and hit the + button. Select Desktop, and input the 'PC Name' (IP Address) name of the RasPi and the username/password for the SSH connection.
Follow the prompts and explore the options. Ignore the "Identity of remote PC can't be verified" warning.
Disappointingly these remote connections don't work like a normal monitor where you use the RasPi's keyboard and mouse and watch them from the 'droid screen. What you get is effectively the RasPi becoming a 'terminal server' and the 'droid becoming like a terminal workstation. So you need to use the 'droid's on-screen keyboard and chase the virtual mouse-pointer around the screen with your finger.
Yes all pretty pointless really. In my opinion complex GUIs like Linux and Windows desktops and others are way too fiddly to try and operate remotely, or with fingers and pointers; remember the iPaq!? I've still got mine. Pain in the arse. Needed a plastic pointer and magnification goggles to use it.That's why simplified mobile phone operating systems were developed, with chunky icons - noone wants to screw around with a pissy little stylus and squint themselves blind. Check out the development of the User Interface.
However, if you enjoy pointless fiddling with unfeasible technology, you may be interested in connecting a RasPi to a touch screen..
The power and utility of 'Nix is really as headless servers configured and operated through SSH. And imagine what you could do if you were also able to control your Raspberry Pi from your smart phone..
AndyM | July 2020