Before USB ports became standard on PCs, several devices connected through a serial port. They're obsolete in many ways, but ...

Serial ports are widely used by sensors for data acquisition, and they were standard on early computers for connecting a modem, mouse and other peripherals. Old Macs used the serial port for printers.

Enter the isolated USB null-modem. The device consists of two USB Communication Device Class, or CDC chips, creating a USB serial port for each attached computer. The TX and RX lines are cross ...