The new solar data logger project is slowly progressing and a part of the project includes some Atmel-based slave boards for measuring sensors in various parts of the house. The slave boards are connected together using a full-duplex RS485 network.
We have already made a full-duplex RS485 board to go on the Raspberry Pi to communicate with the slave sensors but we thought it would be easier for debugging to use a USB device on a PC or Mac to communicate with the sensor boards.
We looked for a full-duplex ready-made adapter but all the ones we found are only half-duplex devices and as we needed to be able to supply 12 volts via the RJ45 connectors on the slave boards we decided to make our own USB to RS485 full duplex adapter using a USB converter chip from FTDI.
The board uses an FT230X ftdichip.com/Products/ICs/FT230X.html with an RS485 converter chip which outputs to a set of header pins and also an RJ45 socket.
The new adapter board can supply power to the slave devices through the USB port or can be powered from an external supply by removing a power selector jumper. The board also has an onboard 120R terminator resistor with a selection jumper and LEDs to show serial activity.
The PCB files and schematic can be downloaded from https://github.com/briandorey/USBtoRS485