In trying to develop a RS485 communication and I had it almost finished.I have 3 arduinos connect on a breadboard using 3 max485 chips using 5 V on power.On breadboard the circuit works well but doesn't the 5V would be very low voltage if I use about 100 meters on utp cable for example?
I understand the RS485 works on differential mode but with this distance ...
Can someone tell me what is the normal differential voltages using standard circuits using rs485?
Should I believe with 5V supply will work on this distance?
From what I can see from a search, 5V seems to be pretty standard for RS485 transceivers. Maybe someone else knows better?
Do some reading of the datasheet.
100m is fine, output voltage is not the big RS232 swing you might be used to.
Make sure to terminate line at the receiving end.
MAX1487-MAX491.pdf (531 KB)
3v3 transceivers are available but 5v is way more common.
but doesn't the 5V would be very low voltage if I use about 100 meters on utp cable
Are you referring to powering the Arduino over UTP?
That distance will have no bearing on the 485 signals, they are designed for 4000' at slow(ish) speeds. As long as the voltage difference on A and B is 200mV or more you are conforming to the spec.
Rob
Are you referring to powering the Arduino over UTP?
No !! I'm just using for RS485 Communication.
200mV or more you are conforming to the spec
I'm surprised , I didn't know the value of the differential could be so low.Could a magnetic interference change this on bought lines?
The idea is that one line is impacted by the same amount as the other line, so the overall difference between the two stays the same.
Ok got that.
Thanks