DMX robust - RDM not? - E1.20 RDM (Remote Device Management) Protocol Forums

Milton Davis · May 24th, 2008

Hello Steve,

The DFD 4 pin terminators are built by request. The design of the Wybron products is such that you are supposed to cable out to the first scroller, daisy chain to the nex, etc. until you get to the last one. The last open connector on the last scroller is supposed to cable back to the power supply. This serves two purposes:
1. The additional cable serves as "doubling up" of the power wires so voltage drop is better controlled.
2. There is a data terminator in the power supply so the act of connecting this loop also terminates the signal.

On those occasions when it is not practical to run the final cable from the last scroller to the power supply, a terminator can be plugged into the end of the line. While this addresses the termination issue, it leave the possability for low voltage particularly at the end of the string of scrollers. Also, just for reference, it is a 2 Watt, 120 ohm resistor connected between pins 2 and 3. We use a 2W part because a 1/4 or 1/2 Watt part might be destroyed in the event of certain connector mis-wiring configuration.

I have not gotten a good sense of the issues prompting this thread, but is is possible that the real cause of problems is one or more scrollers resetting due to a power "brown out"? Given that there is no return cable, the last units may be getting voltage "starved".

Regards,
Milton Davis, Engineer
Doug Fleenor Design, Inc.

May 24th, 2008	#9
Milton Davis Task Group Member Join Date: Aug 2006 Posts: 15	Hello Steve, The DFD 4 pin terminators are built by request. The design of the Wybron products is such that you are supposed to cable out to the first scroller, daisy chain to the nex, etc. until you get to the last one. The last open connector on the last scroller is supposed to cable back to the power supply. This serves two purposes: 1. The additional cable serves as "doubling up" of the power wires so voltage drop is better controlled. 2. There is a data terminator in the power supply so the act of connecting this loop also terminates the signal. On those occasions when it is not practical to run the final cable from the last scroller to the power supply, a terminator can be plugged into the end of the line. While this addresses the termination issue, it leave the possability for low voltage particularly at the end of the string of scrollers. Also, just for reference, it is a 2 Watt, 120 ohm resistor connected between pins 2 and 3. We use a 2W part because a 1/4 or 1/2 Watt part might be destroyed in the event of certain connector mis-wiring configuration. I have not gotten a good sense of the issues prompting this thread, but is is possible that the real cause of problems is one or more scrollers resetting due to a power "brown out"? Given that there is no return cable, the last units may be getting voltage "starved". Regards, Milton Davis, Engineer Doug Fleenor Design, Inc.