Problem with Serial communication (RS485)

Hi,
I have a problem making an RS485 communication between an Arduino and a power meter work. I've ordered a RS485 to TTL converter and have checked that it is working using the RS232 spare port on my STK500 board and a python program using the minimodbus library. Since I did not manage to get a connection with the Arduino Uno, I tried to communicate with the power meter using the passthrough serial Console on my PC like I did with the STK500, but I did not get a valid response. Is my assumption that this should work just as fine as using the STK500 board wrong? What can I do to trouble shoot? I unfortunately only have a very old analogue oscilloscope, but at least I was able to confirm that the Serial port of the arduino is sending out data. If I connect RX and TX, the minicom serial console shows that I can communicate with myself. However, I'm unable to get a bidirectional communication between the Uno and the STK500 RS232 port.

Best,
Sebastian

You forgot to give any details on the meter you are trying to connect to.
Paul

There seem to exist RS485 libraries, even your power meter should have a library or sample code at least.

Otherwise connect the send and receive enable pins of the converter to some Arduino output pins. Enable sending only while you are sending characters to another device and stay in receive mode otherwise. Question is how the power meter knows when to send data - this should be explained in its datasheet or example program.

Hi,
maybe I did not make this clear before - the meter uses a Modbus protocol. It only sends data on request. It is working via passtrough through the RS232 interface on the STK500 (with a python program on my PC), but not with a Serial passtrough of the Arduino (not running any program on the arduino).

Sebastian