This simple converter is built on cheap chinese components. It is connected to a PC via a USB-B connector followed by an ESD protection USBLC6-2SC6. The 5V USB power supply is protected from power surges or short circuits by a MT9700 (or BL2554) current limiter with a limit set at 1.5A. Four CH340C USB to UART converters are connected to the four-channel USB hub CH334U, which are enumerated as virtual COM ports when connected to a PC. The RX, TX, CTS and RTS signals are transferred to the output terminals by capacitive isolators π122M31. The isolated side of the converters is powered by isolated DC-DC converters IVB0105S3V3.