Yorkville LP-DMX3/5 - Manual (Page 8)

“DMX OK” LED
The DMX OK LED lights when the LP-DMX3/LP-DMX5 is receiving a
valid DMX-512 signal from the controller. If the DMX-512 signal stops for
any reason, the DMX OK LED will go out and control will be passed back to
the Yorkville controller input. If no Yorkville controller is connected,
control reverts to the local rotary switches on the LP-LED4.
DMX IN and DMX OUT Connectors
DMX-512 devices are connected in a “daisy chain” arrangement, where a
cable from the controller connects to the DMX IN of a first DMX device.
DMX OUT of that device is connected to DMX IN of a second device and
so on for as many as 32 DMX devices. 32 devices may not seem like much,
but devices are not channels: the LP-LED4 with the LP-DMX3 or LP-
DMX5 may use up to 20 channels, but only counts as one “device.” And it
isn’t necessary to connect the devices in any particular order – the address
makes sure the right channel gets to the right device regardless of its position
in the daisy chain.
The Terminator
A DMX-512 terminator is not part of the LP-DMX3/LP-DMX5, but should
be connected to DMX OUT of the last device in the daisy chain. DMX-512
signals are transmitted as a series of very fast pulses. When they get to the
end of the daisy chain, they tend to bounce back the way they came, toward
the controller, interfering with new pulses coming out. A terminator is just a
resistor of the right size that, to the pulses, it looks like another piece of
cable that goes on forever. The pulses go in and they don’t come back out,
so they don’t interfere. Terminators are available from most stage-lighting
vendors, but if you’re handy with a soldering iron, appendix B is a wiring
diagram for building your own from an XLR male connector and one or two
120 ohm ¼ watt resistors.