One of the first, in the early 1980s, was by Kliegl using a Texas Instruments calculator shell and keypad. (See performer 4 at KlieglBros.com.)
RFU for the ETC Express/Expression3 console family:
The wired RFUs for the ETC Express(ion) and Obsession use the Switchcraft-style, gray-insert, "symmetrical" 6-pin XLR connectors.
See also RFR and iRFR.
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