Hi
I just thought I'd share what I found in this DMX splitter. -I thought it was interesting.
For those not familiar with DMX, it's basically RS585 with a few extra specifications, used in stage lighting to control lights.
The specification says to use 5-pin XLR connectors, but most cheaper gear uses 3-pin XLRs with basically the same pin arrangement as pro audio so microphone cables can be used.
Pin1 = Shield, Pin2 = Data+, Pin3 = Data-
Typically light units get daisy chained in parallel from the main controller, with a termination resistor (120 ohm) at the end of the chain.
Obviously there is a limit to how long these chains can be, so that's where boosters & splitters come in.
Anyway, so I bought this Beamz 8-way splitter for a show I was doing.
https://www.beamzlighting.com/product/dmx8-splitter-booster-8-way/ It has (or is supposed to have) a handy switchable termination resistor built in on it's input.
I noticed that the termination switch wasn't working as it should, but it's an easy thing to work around by using an external terminator (like you would with any other piece of gear). But I was curious what the problem was, so after the show, I opened it up to investigate...
-see pics
What I found was that functionally, the switch & termination resistor were across power & ground, instead of across the DMX differential pair.