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Electronics => Projects, Designs, and Technical Stuff => Topic started by: inevitableavoidance on February 27, 2017, 02:53:04 pm

Title: Extracting power from RS485 / DMX?
Post by: inevitableavoidance on February 27, 2017, 02:53:04 pm

I'm working on a simple DMX to NRF24L01 gateway/translater for some lights I have at home, and was wondering whether it was possible to extract power from the data lines. I'm having trouble finding information about this online. Does anyone have any info/experience on this?

Thank you a lot in advance,
David

Title: Re: Extracting power from RS485 / DMX?
Post by: dmills on February 27, 2017, 06:07:50 pm

You really, really shouldn't, but there are a few things you can do if you are sure your device is the only load on the line (These do NOT scale, and may severely mis terminate the line).

A pair of 50 ohm resistors in series between the data lines will provide 2.5V at a small current from the centre tap, you might get 5-10mA or so this way without messing up the line too badly.

Some products used the second data link pair (pins 4 & 5 on the XLR) for power (In one case for 24V power!), or of course if the second link is another DMX universe and you are not using it (Some of the hogs did this IIRC) then you could use that for 5V with a bridge rectifier made of a couple of low voltage diodes. 

Regards, Dan.