USB to RS485 Adapter

Ethan Zonca
http://www.protofusion.org
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This is a simple USB to RS485 bus adapter. The adapter is designed using a FTDI basic UART chip (FT230XS) and an inexpensive TI differential receiver (SN75176)

Description

While developing the Luma RS485-networked LED driver we discovered a need for a small and inexpensive USB to RS485 adapter. We designed an adapter with a FTDI basic UART chip (FT230XS) and an inexpensive TI differential receiver (SN75176). Our small selection of parts brings the cost down to just over $5 for one adapter.

The adapter has a mini USB port and a surface-mount 8P8C (RJ45) jack. Two LEDs (RX and TX) are located on the left of the USB port, and a white power LED is located on the left of the RJ45 jack.

The RJ45 jack is DMX-compliant, and the solder-jumpers shown on the right of the RJ45 jack optionally connect pins 4 and 5 to +5v. Connecting these jumpers breaks DMX compliance, but allows you to power your custom projects from the bus.

The transmit and receive enable lines on the differential transceiver are connected to the CBUS pins of the FTDI chip, allowing the FTDI chip to control transmit and receive enable automatically.

The functionality of these pins is configurable with the FT-PROG utility. A sample configuration XML file is included in the sources below.