Logic RDM Sniffer

Saleae Logic

The Logic as a 2 line DMX/RDM sniffer

The Saleae Logic makes an excellent DMX / RDM sniffer. With the Logic and a small amount of hardware you can build a sniffer for a fraction of the price of commercial units.

Parts

• A Logic or Logic 16, but see the note below.
• 485 driver circuit
• XLR connectors.

Electrical

You need some hardware to convert from the differential 485 levels to a signal which the logic can understand.

At the basic level you only need an RS-485 receiver like the Maxim MAX485 or Linear Technology LT1785 to translate from the DMX/RDM differential levels to a TTL level that the Saleae Logic Understands. File:Example.jpg

Software

Saleae Logic

The Logic App decoding DMX

Saleae provides the Logic App which works on Windows, Mac and Linux. The application has a plugin to decode DMX, but it doesn't understand RDM data. The tool is best for analyzing the signal timing rather than the high level messages.

OLA Sniffer

OLA has a text-based DMX/RDM sniffer that works with the Logic (it could easily be extended to work with the Logic 16). It can be found in tools/logic directory of the OLA sources.

Limitations:

• the sniffer doesn't understand DUB responses yet since it looks for breaks.
• it may struggle with signal timings that are at the edge of the E1.11 standard. If you experience problems with the sniffer please email the Open Lighting Mailing List