Monitor existing RS485 Modbus data link and extract data... help !!

Using Arduino Networking, Protocols, and Devices
#1

Hi all,
I have a Solar PV system that has an rs485 modbus link from the inverter ( modbus master ) to the Grid Current Transformer module(slave) .

The inverter requests 30 data register values from the slave unit ( address's 31000 to 31029 )
Initially, I need my arduino to read the value of just one of the registers ( 31013~ grid power )

I have previously built an arduino modbus master that will get the required data from the slave , but as only one master per rs485 link is permitted , I cannot run it with the inverter connected.

Is there a way to make the arduino view the inverter / CT unit traffic, identify the packet and make that value available?

I have thought of splitting the RS 485 link and making two links with the arduino as the 'repeater middle man' but this is then making the arduino a critical component.... there must be an easier way .

Thanks in advance.

#2

check out this post:

provided you know the baud rate sniffing the bus should not be a problem with the setup there...

Arduino setup.jpg
Arduino setup.jpg1247×735 171 KB

hope that helps! :slight_smile:

#3

Thanks Sherzaad for your speedy reply,

I know the baud rate ( 9600) parity etc.... it looks like exactly what i need.

Thank you.

Sadly it will be at least 4 weeks before I can get back onto my project :frowning: ( working out of country )

#4