[chbot] Fwd: Raspberry Pi etc.

Starr Moffatt zl3custarr at gmail.com
Tue Aug 17 08:29:28 BST 2021

Hi All,

Thank you for including me as a member.

I was the person that asked for help regards using the Raspberry Pi for 
logging electrical data.

As I thought I might be chatting only to a few people, rather than the 
whole group, I did not have anything prepared.

Thank you for the suggestions. As mentioned it was too much for me to 
remember everything so please also inform me using this list. (Or use my 
email address  zl3custarr at gmail.com )

Please see below more info.

17 AUGUST 2012

The idea for this came about at my brothers place where it was thought 
that maybe due to an “unseen” water leak the water pump would be 
operating at “regular” intervals and therefore consuming electricity.

For this to be checked the best place to monitor the pump circuit is at 
the switchboard.

A clip on a.c. current sensor would be the best option for detecting 
when the pump was operating.

For this to be logged, the current sensor could drive a 4N26 opto 
isolator along with a storage capacitor arrangement on its output, to 
provide a constant signal to the Raspberry Pi’s input while the current 
was flowing to the pump. Note this would not provide a value of current, 
instead just the indication that the pump was on or off.

The Pi would be required to log this on/off state, at regular intervals, 
say 1 minute, along with a time/date stamp. Therefore the Pi would need 
to populate a suitable spread sheet with this data.
Mark, I think you had some suggestions on this so I would appreciate you 
written comments.

Peter Harris suggested I look at Openenergy Monitor which I have done 
and I have found a suitable circuit for the current sensor arrangement. 
Thank you.

Another idea that I am looking at is to be able to check the times that 
a water heating circuit is enabled. This would only need a 230V coil 
relay with a NO contact connected between a Pi supply and one of its 
inputs. This would also require another column to be populated in the 
spread sheet.

In the future:
I am also thinking that it may be of use to record the values of current 
and voltage. Again a spreadsheet would be needed which could also have 
columns for power and, using integration, kWh. I guess an Arduino would 
be simpler as it has built in A to D conversion, however as I already 
have the Pi I will persevere with it at this stage. Just looking at the 
drawing for the current sensor for the Arduino; 

it looks as if the software determines the peak value and from there 
calculate the RMS value. I assume the voltage RMS value will also be 
calculated using the peak value as well. I have heard that the scan rate 
of the Pi is slower than the Arduino so I wonder if this would have a 
bearing  on the Pi’s ability to determine the peak value.


Starr Moffatt

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