Hi Terry,
Sorry for the late reply. ?I haven't any direct experience of using a Pi with the Arduino DCC++ standard base station but I have played with JMRI DCC++ in conjunction with my own Arduino sketch. ?There may be some simple checks worth doing if you have not already done so. ?I assume here that you're using a USB/serial connection rather than the Ethernet option.
Can you load a new sketch on to the Arduino from the Pi using the IDE? ?It's worth while checking this to ensure it's not h/w connection related.
What do you see on the DCC++ traffic monitor (Panel Pro -> DCC++ -> DCC++ Traffic Monitor)? ?You should see JMRI periodically issuing 'Status Cmd' which should elicit some response from the Arduino.
Regards
Paul
