Hello can i use my usb pc port to charge up 2 nanos for a test? So i a using 2 of them to make a RS485 connection
Not quite sure what you are trying to say. One USB port connected to two Nanos? Are you going to cut/split a USB cable? Why not use twi USB ports?
As long as your current consumption is less than 500mA for a USB 2.0 port and less than 900mA for a USB3.0 port then yes you can power more than one arduino.
What length of cabling? What total current draw? You have to check the total
resistance of the cable isn't a problem.
Nano's aren't batteries, so why say "charge up 2 nanos"? Do you just mean "power up",
or are there batteries as well?
i meant power up two nanos on two different usb ports
i meant power up two nanos on two different usb ports, so they both can get energy but do i need to put a resistor? i already have to in the rs485 on DE and RE
i meant power up two nanos on two different usb ports, so they both can get energy but do i need to put a resistor? i already have to in the rs485 on DE and RE, the cat 6 cable on the A and B in the resistor is 150m long
You need resistors on the RS485; see e.g. https://www.gammon.com.au/forum/?id=11428
Compare the schematic of your modules with that in the link that I provided.
i made something similiar of what u send me
for example on the resistor in A and B i puted the resistor right next to then, i didnt find a 120ohns one so i used an 820ohns
The 120 ohms resistor is a terminatig resistor to prevent reflections. It is suggested that it it used at the far ends of the cable between A and B line not from A to VCC and from B to GND !
The resistors from VCC and GND are bias resistors and they do put a load on the line. In modern tranceivers they are not needed .
Also be careful with that since different chip manfacturers use A and B symbols in a different way. A may be the "idle high" line or the "idle low" line and the oposit goes for B
Take a good look at the RS422/485 standards before implementing the resistors.
You can find info here:
or google for ANSI RS422 / RS485
The cable length is fine for RS422/485. You will need the 120 Ohm terminating resistors between A and B lines at each far end.
P.S
Do not forget to provide common groud but be extra carefull not to create ground loop between the arduinos.
If both are powered from the same PSU or PC USB port then do not use extra wire to tie their grounds together.
i didnt understant part much, can u explain again again please
The RS422 is not a 4 wire system(2 for TX and 2 for RX). It is actually a 3 wire system. Likewise RS485 is not a 2 wire system. It is a 3 wire system. Data flows from A and B lines with reference to common ground between the two devices.
The concept of grounding RS422/RS485 devices is confusing. Please read the below document and pay special attention to paragraph 2.4.4 page 12 (RS422/485 and grounding).
Long story short: If both your arduinos will be powerd from the same PSU or both of them from separate PSU that are both grounded and connected to the same circuit braker then you are just fine using only the A and B wires for communication.
If your arduinos have no common ground between them then it may be a good idea to provide a third wire between their GND's after reading about the ground loops problem and how to face it.
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