Shield for RS-422 over CAT5 with USB for a host

Similar projects worth following
It connects a host computer to an AVR MCU by way of a multi-drop RS-422 bus with an additional RS-485 pair for management (e.g. boot loading).

I use this to connect to some AVR boards I'm working on (e.g. RPUno). The FTDI UART to USB bridge is working well with Linux (I use Ubuntu and Raspbian). The bridge also works on Windows but mostly I use SSH to the Linux machine and then do things from a terminal session (e.g. Picocom). There are two data paths, one is RS-422 and the other RS-485. The RS-422 path connects the FTDI RX to the MCU TX and FTDI TX to MCU RX. While the RS-485 is used for management (e.g. the DTR signal is to run a bootloader). RS-422 is full duplex and works with optiboot and avrdude once placed in a point to point mode. Looking at the MCU TX signal, it can be seen to go from the MCU to a transceiver input which drives the differential TX pair and then to a differential receiver (same U2 chip has both) that drives the FTDI RX. The differential pairs are shared over CAT5 to other boards with RPUadpt shield(s). The transceiver can also be disabled (e.g. a sort of lockout) by the bus manager to prevent the MCU or FTDI UART from using the differential pair.

View all 2 project logs

Enjoy this project?



ronald.sutherland wrote 11/16/2016 at 22:52 point

CAT5 has four twisted pairs, which have well-defined transmission line characteristics with very good noise immunity. At RS-485 speeds and signal levels, they should be able to carry the data for over 1 km (3000 ft). The DB-9 with RS-232 levels can work at up to 1/10 of that distance but has poor noise immunity and is probably better suited for runs that are 1/100 of that distance. My goal is to use a CAT5 daisy chain between a number of solar powered boards (e.g. RPUno) in my yard.

  Are you sure? yes | no

Alex Martin wrote 11/16/2016 at 22:30 point

What is the advantage of using cat5 instead of a more standard db connector?

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates