Connecting bus couplers; am I in for trouble?

I've got a non-cbus 4-button / 4-LED keypad that I'd like to tie into my system. No problem, right -- a pair of 2-channel bus couplers should do the trick? But...

This switch ties one side of all the switches to a common connection, and also ties together the anodes of all the LEDs. That means I'd be wiring together the two bus couplers on the common side of their switch sensors, and also on all their LED drivers. Should I be worried that there will be a potential difference setting up current flow between the couplers? I guess I can just try it, but if I'm about to wreck hundreds of dollars worth of cbus parts it would be nice to know ahead of time.

 

Since you want to wire in remote LEDs, I'll assume you're talking about the 5102BCLEDL, which is the 2-channel bus coupler.

The switches will work fine but the LEDs will not. The 2-Channel Bus Coupler needs to have individual connection to each side of the LEDs and these cannot be coupled together.

 

thanks. i just found a note in
http://www3.clipsal.com/cis/pdf_files/5102BCLEDL_Instructions.pdf
that
"The 1K and 2A outputs are linked internally"
which would clearly prevent this from working. this footnote seems to have been dropped from the more recent documentation that came with my unit:
http://ecatalog.squared.com/pubs/Po...ontrol Products/Input Units/63249-420-236.pdf
but i confirmed that it's true.

the other thing i discovered is that the "LED Drive Output" information at
http://ecatalog.squared.com/pubs/Po...g Control Products/Input Units/1250HO0603.pdf
appears to be completely fictional; the bus coupler actually wants to drive the LEDs at 15mA, and if you believe those instructions and include a resistor to keep the current at 2mA it starts behaving very erratically.

 

Yep, you're correct. The 1K and 2A terminals are linked internally, as you've confirmed. The 2 LEDs are actually in series with each other, so if you put them in any kind of parallel combination then the LEDs won't work as you expect them to.

You definitely don't want to be limiting the current through the LEDs. The Bus Coupler provides a fixed amount of current through the LEDs, regardless of their forward voltage drop. If you try and limit this then it's going to upset the internal power supply. You shouldn't be using any kind of series limiting resistor. If you want to decrease the current flowing through the LEDs then the only way is to put a resistor in parallel with the LED to bleed some current past it.

Thanks for pointing out those errors in the documentation. I've passed that info on to the relevant people so hopefully it will be corrected soon.