EmonPi Lite?

Me and a couple of friends wanted to get into home energy monitoring. The EmonPi is really great but I think its travelled a bit too far from what it had originally started out like. I would prefer something a little smaller and simpler. An EmonPi lite essentially. I want it to

   1. Comply with the Rasp Pi hat standard
   2. Run the standard EmonPi firmware
   3. Use through hole components to simplify home builds
   4. Have all the connector on the same side as the Pis power connector.

I've gone through a couple of design iterations and this is what I have come up with.

As you can see when mated to a Pi A+ its pretty small compared to the full fat EmonPi. The LCD and buttons are still supported though I haven't really used these. To simplify the design the hat pulls all its power from the Rasp Pi. As it uses a 40 way gpio connector it can only be used with Pi's which have a switching power supply. There seems to be enough margin on these supplies and they don't have any problems keeping up with a little extra current draw.

To help support the use of through hole components I've made a few changes. The serial programming connector has gone as I was a little short on space. This hasn't been a problem as I use an adaptor to program it though the gpio port or i just use the ISP connector instead. Second, as the through hole 328 doesn't have an A6 pin I routed the unused A0 pin to the RJ45 connector instead. I doubt I will ever use this input so I should never need to deviate from the standard firmware. Also the circuit around the mains voltage input has also been simplified as the hat will never pull power from it so AC coupling onto the measurement circuit in is not necessary. Finally I've included  the option for a 6 way 0.1' header as an alternative to the rj45 connector. I find this connector easier to work with at home. They share the same board space so it's an either or population.

I have built 3 of these hats so far and have had mine working for just over a month. I'm using it to monitor one current, mains voltage, my gas meter via a hall sensor and two temperatures. I'm really pleased with it. The whole setup can be run off of a spare USB port on the back of my router saving an extra mains socket.

Any observations or suggestions you guys might have would be much appreciated.


Bill Thomson's picture

Re: EmonPi Lite?

Nice work! Clean, small package. Looks really good!

johlhausen's picture

Re: EmonPi Lite?

Very clean indeed! This could be a neat way to monitor mains current/voltage/gas in a residential application. Could a power supply be modified to provide 5VDC to the Pi and 9VAC to the voltage input, thereby having only one power connection?

mrscruffy's picture

Re: EmonPi Lite?

I guess so. I would have to sacrifice the eprom or switch over to surface mount to get the required board space. Might as well do a respin for the Pi Zero and make it smaller still. 

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