In message , Big Bad Bob
 writes
>On 2019-08-07 13:40, Dave Liquorice wrote:
>> On Tue, 6 Aug 2019 20:17:42 +0100, Adrian wrote:
>>
>>> I've tried unplugging the gauge, but I still get the problem,
>>>suggesting
>>> GPIO rather than the gauge itself.  Stopping and restarting the software
>>> appeared to help for a couple of days, but it has started again.
>>> Rebooting doesn't work either.   The Python3 code below is started at
>>> boot up, and can be run with nohup.  Any suggestions on where to start
>>> looking ?
>>  Had any thunderstorms recently? Suspect a hardware problem, damaged
>> GPIO input, or the built in pull up/down resitors fried. A floating
>> input can produce a stream of false transitions. Either try another
>> GPIO for the guage or fit a 10 k or so pull up/down resistor as
>> required.
>>  Then think about adding some protection to try and reduce the
>>chances
>> of the Pi getting zapped again.
>>
>
>moisture and bad ground connections also a possbility.  months of
>"sitting there" and you get galvanic corrision.  If it's anywhere near
>rain, you might need to use some kind of coating to waterproof it.
>
>Moisture plus electricity (even low current) can lead to galvanic
>corrosion, tin whiskers, mold, leftover flux turning into a conductor,
>insulation breakdown, lots of very bad things.
>
>additionally, the idea of an external resistor (where you were using an
>internal pullup/down resistor) is probably a good idea anyway, to help
>protect electronics against static discharge and noise in general.
>
>

Thanks for the follow up.

I can only agree with the first two points, and I'm not in a position to
comment on the last one.

The PI is in a IP55 enclosure
(https://cpc.farnell.com/olan/ol20112/box-ip55-glanded-150x110x70mm/dp/EN
82191), which in turn is mounted about 8ft above floor level in my
garage, and the grommets have been trimmed to the minimum required to
get the cabling through.

As stated elsewhere in the thread, the problem has been seen to persist
when the rain gauge is unplugged, suggesting that the problem is with
the PI Hat or the Pi itself.  However, as time has passed, the problem
has changed.  The fault has become more intermittent, and now it tends
to show up when there is rain, but not always.  With rain expected later
this week, it will be interesting to see what the outcome is.

Adrian
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