Electronic – MAX485 problem on signal with Arduino


I'm trying to do communicating an Arduino Mega to an Arduino Nano through RS485 protocol.

In this way, I'm using two MAX485 boards like this :
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If I apply this wiring :
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I get this signal :
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As you can see, the signal output from A and B are same and a little distorded at the beginning.
Would you have an idea why ?


Best Answer

It is probably due to the fact that you have not connected up the VCC and GND to the two modules. The initial communications transitions are back feeding the VCC and GND through the input protection diodes of the MAX485 until the C1 bypass capacitor gets charged up to a stable value.

Make sure not to run your RS485 transceivers without power applied.

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