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Topic: RS485 Switch the termination resistor (Read 858 times) previous topic - next topic

davivid

I want to have an status LED that show's whether the Node has its termination resistor enabled or not.
I figured the MCU would read a switch, set the status LED as required, and engage the resistor - but how best to do this? (without affecting its impedance)
Or is there a better option?

CrossRoads

So you're going to have like a DG418
http://www.maximintegrated.com/datasheet/index.mvp/id/3129
wired in series with a termination resistor and open/close it?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

davivid

Yes that's the kind of thing I was thinking, just wasn't sure of the 'correct' way to accomplish it.
Thanks for DG418 tip!

Papa G

You could use drivers like the LTC2871 that have built-in, selectable termination resistors but they are kinda spendy and don't come in very handy packages.

If you use a switch like the DG418 you'll probably have to tweak the value of the resistor to get the equivalent value close to 120R.

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