My problem is quite simple, I need to log the date and time when a light is switched on and off. Whatever monitoring equipment is used it must be able to store the data for up to a month. The equipment will be located in a remote cabinet which does not have access to either wifi or ethernet connections. Ideally the data would be downloaded by a cable connection to a PC. Assuming the data would be held on an SD card it could be plugged directly into the PC.
I am looking for the cheapest solution to this problem and I thought that an EmonPi would be suitable but I cannot see where I can buy one from.
Are they still available? or is there any cheaper/alternative solution.
Many thanks for reading this, I hope you can supply an answer.
Have you tried the OEM shop?
Welcome, John, to the OEM forum.
Obviously, @Vster didn’t check The Shop first. As far as I know, The Shop did have a stock of Atmel ATMega328P processors, on which the emonPi depends, when it became clear that semiconductors would be in short supply, but as the emonPi isn’t listed, I suspect that stock has probably run out now.
I presume you were thinking of measuring the current or voltage to the lamp in order to determine whether it was on or off. But if you only need to know on or off, all you need is whether the voltage or current is more than nothing. And for that, by far the easiest is to take the voltage, half-wave rectify it and feed an opto-isolator and there you have have a pure digital signal that you can feed straight into a basic (even second-hand) Raspberry Pi - without the complications of the “emon” part. Both will give you a train of pulses and you can deal with that - detect when they’ve really stopped - in software.
If you need to set this up on the supply side of the switch, then you’ll need to use the current rather than voltage. In this case, you need a small current transformer instead of the opto-isolator, and everything else is much the same.
If you want to try this approach, I can go into a bit more detail.
I’ve recently bought one of these which might help:
1 Channel AC 220V Optocoupler Isolation Module High Voltage Opto Isolator 3-5V Power Suppply PLC Photoelectricity Coupler Module
Much as Robert suggested, except ready made. If 240VAC is present, the 3-5 V output goes high (or low). Can be easily integrated into OEM I suspect.
I got mine on ebay, but couldn’t find the original link.
There is also an on-line video that explains how the circuit works and how to modify it for different applications.
Continuing the discussion from Can you still Purchase EmonPi?:
Hi Robert and Anthony
Thanks for the helpful replies. I rather suspected that as the EmonPi was not listed on the OEM Shop there were non available.
At present I can only get to the supply side so it’s the current transformer route, alternatively I can get to the electricty meters optical pulse output, but I intend to look into getting to the output side of the switch so the optoisolator would also be feasible.
Your comments have made me think the use of EmonPi or EmonTx would be using a sledgehanner to crack a walnut! As a result I will look to use an old Pi I have or even an Arduino Uno.
I couldn’t find the on-line video for the isolator but I’ll keep looking, unless you have a link?
Once again, Thanks for the help, you’ve both pointed me in the correct direction.
The old emonPi V1 is not available, however the same functionality plus more can be achieved using an emonTx V4 + emonBase.
We’ve also got an emonPi V2 in the pipeline which should be ready in around 3 months.