Almost worked out of the box/zip. At first I wondered what ‘Connection string’ could refer to during integration setup. Only variable to be known to me here was the serial port, so indeed it needed /dev/ttyUSB0 here. I suggest just asking for ‘port’ or ‘serial port’ and maybe pre-fill the field with /dev/ttyUSB0, which would be most common, if possible.
Had to remove previous plugwise references from configuration.yaml, probably to make the serial port available for this integration. All I got was a connection failed at first.
Some initial data seems to have come in, it even found my Stealth (which is not much more than a Circle in a different enclosure). For most plugs I only have 1 or 2 initial data points in the last 20 minutes, which suggests it has trouble retrieving data I guess. In home-assistant.log I see many warnings, for example:
2020-03-28 15:45:23 WARNING (send_messages_deamon) [plugwise] Resend NodePingRequest for 000D6F00004EEB0A (b'0196') because stick did not acknowledged send request
2020-03-28 15:45:24 WARNING (send_messages_deamon) [plugwise] Resend CirclePowerUsageRequest for 000D6F00004EEB0A (b'0196') because stick did not acknowledged send request
this happened for all Circles, also Circle+.
Figured I’d set the logging to debug, restart HA and try again. This time all seemed to work and am still getting data points for most devices. Will test some more and report back later.