Troubleshooting guide

USB Interference
Interference and USB connections
Why interference should cause problems with USB connections doesn’t seem to be well understood, but it
does definitely seem to be the case that USB connections are more sensitive to external interference than,
for example, traditional RS232 connections. Whether this is perhaps because of the much higher design
speeds of USB connections, lower voltages used or whatever else isn’t generally explained, except perhaps
in the professional electronics literature. It is known that Davis expended considerable time and effort in
extensive investigations of this problem with the USB logger connections, including looking at alternative
USB chipsets such as FTDI, but were unable to identify any specific cause or definitive fix other than the
general issue of external interference. And it is a fact that taking steps to minimise the effects of external
interference often results in mitigation and – if you’re lucky – disappearance of the USB dropout issue. So
the issue does seem to be strongly linked to local interference even if the precise nature of the link is
unclear.
There seem to be two main sources of interference, which will need to be investigated separately: through-
air wireless interference and noise or interference propagated through the AC mains (ie via the mains
adapter powering the console/logger unit). And there is a range of possible fixes for this interference
problem suggested below, the diversity of the suggestions reflecting the rather ill-defined nature of the
problem and the difficulty of knowing which one is most likely to work in any given instance. All we can
suggest is that you review the various fixes and, if necessary, work through them in turn to see which might
be the best option in your specific case, starting obviously with the simpler and cheaper options. The
starting point is to review the three simple fixes and see whether any of these helps, before moving on to
the other options:
Simple fixes
• If you use the Davis Weatherlink software (as supplied with the USB logger) then ensure that you
have updated this to the latest available version (v6.0.3 at the time of writing). The USB driver which
is packaged with Weatherlink is updated from time to time with specific fixes to minimise the USB
dropout problem. (Users of non-Davis software can also install the latest Weatherlink version even if
they don’t use it regularly. This will ensure that the latest USB driver is also installed on the PC.)
• Look around the immediate environment of your USB connection and see if there is anything there
that could credibly be generating interference, eg cordless or mobile phones, baby alarms, any
computers or other devices runing with the covers off, fluorescent lights etc and if possible take steps
to move any such items well away from the logger-PC connection – the further the better. Also, route
Prodata Weather Systems Davis Weather Stations KB - Prodata Weather Systems - 1
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