…and any other programmable board you can find in the market!
How you can upgrade or enhance you 3d printer to do lot more than usual? Use one of these programmable boards ( only if you know how and what to do ). Capabilities? from few to too much. Prices? from 35 Euro to some hundreds. You choose!
Excellent! RasPi is the most affordable with lots of abilities anyone can purchase. Lots of scrips have been uploaded in GitHub for such uses!
With Arduino let say UNO, could clean the nozzle with a single command…
Just for Info: You don´t need a Raspberry Pi 4 for that.
Even the good old raspberry pi 1 works fine. It for sure depends on the number of plugins, but when you have a spare Pi1 the upgrade is for free.
Pi Zero: Does not work! The Wifi chip is different and takes away CPU load, which may cause prints to fail.
Pi1: Works basically fine. Uploading files may take a while, Camera is fine. The interface/booting takes some time and you should not overdue using plugins. I mostly use the PowerControl Plugin, which allows to turn on/off the rest of the printer, while the pi is running 24/7. I use one on my Anet A8 for ABS printing within the enclosure for years, so I can say it is a robust solution.
Pi2-Pi3: These are fine and snappy. Uploading files to a Pi3 is faster than on a Pi2, but that was to be expected.
Pi4: Overkill in most cases. Just use if you want to use cpu intensive plugins. The Pi4 is better used, when used with Kodi 
The combination with the pi cam module is just great and allow very nice optical monitoring of your printer. Better get a second hand Pi3 and a camera than just the pi4 for the same amount money
Yesterday, I started using a Huawei P20 I have lying around (because I would never use it as a phone, for security reasons). I’m using it with DroidCam to keep an eye on my prints. It’s pretty nice. I may even pay the $5 to get the Pro version of DroidCam to gain the better camera controls (including zoom).