Several years ago I purchased and assembled a Pi 3 kit. Can I now change out the Pi 3 for a Pi 4 using the same case?
It depends on the design of the case but most likely not without some hackery.
The basic shape and mounting hole locations of the "B series" pi models has remained the same since the pi 1 model b+. However the 4B (there is no 4a currently, there may or may not be one in the future) made substantial changes to the port types and locations.
- The Ethernet aocket and one of the pairs of usb sockets were swapped.
- The "power in" connector was changed from a USB micro B to a USB C.
- The full sized hdmi port was replaced with two micro HDMI.
In addition, compared to the the 3B, the 3B+ and 4B add a POE header which can get in the way sometimes.
And of course component layouts change between models.
So if your case is a large box with space for cables inside (like the naturebytes case) or your case only covers the top and bottom and leave the sides open (lile the pihut cluster case). Then the pi4 will probablly fit ok.
If your case is a typical desktop case with plastic or metal around the ports the some hackery to said plastic will probably be needed to make it fit.
and if your case is an especially tight fitting one like the pibow then you have little hope making it fit.
Yes, you can, but you probably don't want to. I've crammed a Rpi4 into a Rpi3 case, but it wasn't pretty. Had to Dremel out plastic and the lid never fit right. Maybe wasteful of me, but I bought a new case.
I've also built my own cases. Ferinstance, A Peter Frampton cassette tape case can be Dremeled into shape for a Raspberry PI. It worked, but then it looked like a cassette tape case I'd Dremeled into shape...
You might consider building a case from Lego bricks.
I have a Raspberry Pi cluster in a transparent lucite case, but it needed something to keep drives and power and switch tidy. I bought a bunch of transparent Legos and some LED-lighted Legos to build something pretty. Transparent Legos catch the light of LEDs from the Raspberry Pi and the attached peripherals quite nicely.