Sure you can just surf the net and pretty much let your PC be a (pardon the term) “Boob tube”. Why not let it be more? Hopefully I can just scratch the surface to allow you to see what really can be done with a personal computer aka PC (not just a computer running Microsoft Windows).
Newer pc’s today seem to be losing the traditional ports (where we can plug things in) on the newer pc’s. It is almost worth it to keep an old pc around. Sure usb can let you add things, but usually you have to have a special set up to take advantage of the usb interface. Though eventually everything gets stored digitally in your computer as either ones or zeros, you can still either collect real world data or control other devices.
What are the traditional devices we can use? The parallel, serial, soundcard, and joystick ports. Generally the parallel port only deals with digital input and output. That is is a switch closed or open? (Switch example) You can also send data as if printing to a printer to turn devices on and off. (Control example). You can also use the pc to take a temperature or use other real world data.. Though pc’s usually only deal with on’s or off’s, you can use the built in ADCs (analog to digital converters). (Sound card example) (Joyrstick port example) You can use a traditional pc as a science lab. You can also use the pc to do home automation. a sort of legless robot. (Home automation example 1) (Home automation example 2)
You can think of a pc as the new educational science kit. Guess what I am getting at is you do not have to dispose of that old computer just yet. Give it other uses. Definitely do not throw away those old cables as they can be modified for all the projects previously mentioned. A computer as well as a brain is a terrible thing to waste.