Also very inexpensive to make, a MAX232 or MAX485 chip costs cents and will allow you to connect to any microcontroller. For sensors and similar stuff it's idea

Also very inexpensive to make, a MAX232 or MAX485 chip costs cents and will allow you to connect to any microcontroller. For sensors and similar stuff it's ideal, more 485 than 232 because with 485 you can have multiple devices on a bus (but unlike 232 is half-duplex).