I was just thinking, if I were trying to do this, I'd be needing to measure
live to neutral on a small load, and the resistance of the earth to neutral
or maybe anything that is being generated between them. anything else will
be seen by the other measurement. However its important to run a load
realistically during the times of monitoring and also switching any loads
that could be connected to see how it responds. I've measured lots of spikes
on mains when very little is actually running, but when things are running
particularly resistive loads like heaters or cookers, the spikes are fewer,
making me think much of it is just generated by some other reactive loads
switching.
Not able to do this now of course, but look on a scope at unfiltered and
unloaded mains and its a wonder that it works!

Brian

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"newshound" wrote in message
o.uk...
On 12/04/2018 13:05, Theo wrote:
newshound wrote:
For reasons I won't bore you with, I'm interested in building a cheap,
simple data logger to monitor mains voltage, ideally two channels (live
to earth and neutral to earth). In the dim and distant past I have
designed and built such things more or less from scratch, but surely
someone has already done this.

What do you want to do with the data when you've measured it?

Theo

I'm trying to see if there are overvoltage transients on a farm site,
and/or what the neutral is doing. Slow, rather than fast transients. I
recognise that the arduino analogue inputs are multiplexed.

So, I want to collect data for a week or so, then pop it into Excel to see
if anything is going on.

Would you go for Arduino rather than adding an ADC to a Pi?