Hi all,

I am using a TFA Nexus weather station which is know for losing its sensors 
if connected to USB. The usage of a long USB cable with ferrites on either 
end made it better, but a real improvement was the deactivation of USB 
power after every import which is easy to handle on a raspberry pi with 
uhubctl.

Until now the following line is implemented in crontab and executed every 
15 minutes:

sudo uhubctl - a on -p 2 && sudo service weewx start && sleep 10 && sudo 
wee_reports /etc/weewx/weewx.conf && sleep 5 && sudo service weewx stop && 
sudo uhubctl -a off -p 2

Because USB power is just switched on for several seconds, connection to 
the sensors is not lost any more (exceptions possible), but I see 
disadvantages because of the multiple terminations of weewx. The graphs 
show missing data entries, the regular archive interval is interrupted and 
- the worst thing in my eyes - after every start of weewx all report files 
are recreated, e.g. every jpg file, favicon.ico etc. These files usually 
only are created once after start, and on further archive periods only the 
files are recreated which are stated in the skin.conf.

I know I could improve my graphs by using 'line_gap_fraction 
<http://weewx.com/docs/customizing.htm#line_gap_fraction>' or to change the 
skin.conf to avoid the multiple creation of report files. But instead I 
would like to start weewx only once and to switch on USB power just for the 
short period of the data import. Following things would be possible:

- in crontab just switch on/off USB every 15 minutes and in weewx set up 
archive interval also to 15 minutes, hoping that both events correspond 
long-lasting.
Disadvantage: I do not know how to harmonize both events so that USB is 
certainly active if the archive interval starts. Moreover, it could be 
dangerous if the USB connection was terminated within a data import.

- let weewx execute the switch of USB with uhubctl
Every time before data is imported by weewx from the weather station, weewx 
should switch on USB, when import is complete it should turn off USB using 
'sudo uhubctl - a on/off p 2'. Would this be possible?

Great, but I do not have a clue about implementing this feature in weewx. 
Any ideas? Could this be solved easily just by inserting a command in a 
skin or report? The ftp report for example also causes console commands, 
doesn't it?

Thanks for your help and ideas,
Andreas

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