Printer is "not connected"
If you find that your printer is marked "Unconnected", it means that your Raspberry Pi cannot communicate with your printer. There can be several reasons why this message comes up:
There are several types of USB cables and they are not all built equally. Many Micro USB cables are made solely to charge gadgets like phones and headsets. This prevents the cable from transmitting data that the printer needs. If the cable is very thin, it is a good sign that it does not have all the conductors needed to transfer data.
When using a cable that needs to transfer data around a 3D printer, the problem with the cable can occur due to all the motors being under high voltage. They create magnetic fields that can interfere with the signal through the cable and therefore we shout that you use a shielded cable. These cables have a layer of metal around the conductors inside the cable and are generally a lot thicker than the "normal" cables. This keeps the motors and wires to them from interfering with the data moving through the cable.
Power on the printer
Some printers cannot connect via USB when the power supply is not turned on. Therefore, make sure that your printer is plugged in and the printer power switch is on.
Unplug the USB connector from the printer
It may just need a restart. Unplug the USB plug from your printer and make sure the printer turns off completely. Wait 30 seconds, and then turn on the printer. The USB connector can then be plugged into the printer again, giving it up to 30 seconds to connect to the printer.
Incorrect USB port
The new Raspberry Pi 4 has 2 types of USB ports you can connect your printer to. There are 2 blue and 2 black ports. The blue ports are USB 3.0 and are a newer standard than the old USB 2.0 as the black ports would be. Some older printers have trouble talking to the USB 3.0 standard. Try plugging the USB connector into one of the black USB ports and see if that solves the problem. On the other hand, the blue ports are good for attaching cameras
If the other 2 solutions do not work, you can find an OctoPrint button inside the control panel if you are on the same network as your printer. OctoPrint will load and on the top left side, there should be a "Connect" button that can solve the problem from time to time.
Turn off the "Automatically connect printer" setting in your SimplyPrint printer settings. This prevents SimplyPrint from trying to connect to the printer automatically. Sometimes, especially on older printers, it can "stress" the connection if asked too many times. Turn off this setting, remember to scroll down and save. Then go into OctoPrint and try to connect manually.