Connecting multiple RS485 together

Question

I am trying to build communication across multiple Arduino using RS485. When i am trying to connect 3 Arudino nano together using breadboard my code doesn't reach slave where as if i just if i do direct connection between 2 RS485 without breadboard it works but i use breadboard for 2 it doesn't work. Am i missing any setup here?

Breadboard connection - A & B are connected to + & - of both RS485.

Working connection - A & B of first RS485 connected to A & B of 2nd RS485.

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• Juraj: show a picture of the breadboard version

Answer 1

It is possible you have too many resistors on the RS485 bus. From the RS485 wikipedia page there is this quote:

Ideally, the two ends of the cable will have a termination resistor connected across the two wires.

This may explain why you can use 2 of your RS485 interfaces but not 3. Consider removing the resistors from the RS485 board in the middle if possible.

• Akshay: problem is even if i use only 2 with breadboard it doesn't work. It only work when i connect them directly ? Do i have to use any resistor on breadboard ?
• st2000: Breadboards are not good with high frequencies. Try slowing down the baud rate. Also check if you are using the breadboard correctly. So, 2 connected using wires works? And 3 connected using wires works? But 2 connected using the breadboard does not work? And exactly which TTL to RS485 adapter are you using? Have you added termination resistors to the ends of your RS485 bus?
• chrisl: The thing with termination resistors is, that it's value should be the wave resistance of the specific cable at that specific frequency. I don't think, that this is critical here, as long as the OP does not use too high baudrates. But the breadboard might be the real problem here.