You can install the touch driver for 3.5″touch screen on an existing system, but it just supports raspbian and ubuntu system.

Raspberry Pi must be connected to the Internet,and you can control it through ssh,vnc, Remote desktop or the other big HDMI display.

touchscreen

Step 1:Open the command terminal,Enter the following commands to download the 3.5″touch screen driver;
sudo git clone https://github.com/kedei/LCD_driver

Step 2:Change file permissions;
sudo chmod -R 777 LCD_driver

Step 3:Enter the folder;
cd LCD_driver

Step 4:Install the driver, RaspberryPi will auto reboot ;
./LCD35_show

You can use the following command to rotate the screen 

Rotate 90°    ./LCD35_show 90

Rotate 180°    ./LCD35_show 180

Rotate 270°   ./LCD35_show 270

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