Thursday, May 7, 2020

ADE7816 Energy Monitor

I have been meaning to try out the ADE7816 Single-phase 6 current channels energy monitor for a while. However time has been lacking for the last couple of years. Finally I have a working version with successful board bring-up and a semi-working Micropython driver, with an Arduino driver in the works.

PCB Design

The PCB design process for this was not easy mostly due to a footprint choice mistake on my part. I had placed the 5x5mm QFN part instead of the 6x6mm QFN part in KiCAD. This made the DRC fail everywhere in standard settings. However it ended up being a collaboration opportunity with Greg Davill who loves to practice and photograph bodging stuff. So I now have a work of art at hand instead of a non-functional board.

I am even debating whether to place the rest of the parts and possibly take away from the dead-bug awesomeness. Next time need to order parts in advance and make sure I do 1-1 prints to verify footprints before pulling the trigger on PCB's.

Energy Montor Details

Now to more about the energy monitor. This ASIC features 3 single-ended and 3 differential current inputs and a single-phase voltage input, all in very compact 40-pin 6x6mm QFN package. In fact the PCB is large on purpose to accomodate ease of use with stereo-jack type current clamps. The main usage would be in standard households where there are typically 3-4 lighting circuits, 1-2 socket circuits and dedicated Air Conditioning circuit. A single energy monitor could be built to monitor all channels using a single-ASIC and leave out fancy NILM stuff from worrying about the lights. The socket circuits could have anything plugged into them and can potentially have point-of-load monitoring instead of breaker board based monitoring. All this translates to more data being generated for IoT platforms and some sensible firmware work needs to be done to handle that.

ADE7816 Driver Development

This is still work in progress. I have done some initial exploration to find prior art. Nothing exists yet from Arduino however there is some register lists from a Javascript driver written for the now defunct Intel Edison.

Intel never quite had the maker market pinned right to market that board, it makes me sad to think of all the engineering ours sunk into a now defunct platform. Open-source software / hardware helps us salvage some of that. I also sped up the register listing by copy-pasting the ubquitous table from the ADE7816 datasheet and dropping it into a Jupyter notebook to parse all the registers, not as fancy as the Pdf parser I had built before, but much more reliable.

My driver development follwed the now tried and tested Micropython + Jupyter Notebook + Logic Analyzer path. I used an ESP32 feather as host processor with standard micropython loaded and probed the SPI bus with read-write packets for known registers until the protocol gave in and started responding with some values. The ASIC is super versatile in supported protocols - I2C Slave, SPI Master and SPI Slave modes are all viable. So developing a fully functional driver supporting all the possible modes will take a while. The initial work so far is on the SPI slave mode since all my other work in DIN rail and Featherwing formats is linked to the SPI bus, however the I2C mode can be really interesting for host-processors with fewer pins and flaky SPI support (while having solid I2C support - like the Onion).

If anyone is interested in driver development I am happy to send you a board or you can get one yourself from Oshpark, Aisler or PCBWay. Once the drivers mature I will list it for a wider audience on Tindie.

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