Sunday, November 18, 2018

TPLink Smart Plug Teardown

A while ago I remember watching a youtube video from about x10 years ago talking about distributed social network platforms running on SheevaPlugs. Fast forward 10 years, we are still in walled gardens of internet behemoths like Facebook, Twitter and Google and energy monitors are running full-linux os'es in smart plugs (albeit it is mostly OpenWRT/Lede)

The idea of re-purposing Atheros/Qualcomm router IC's as general purpose linux based controllers is not new. All those pins dedicated for ethernet ports are converted into GPIO's with proper muxing.

I have been designing one myself to fit in the DIN rail using the Onion Omega 2 as the host processor. There are some road-blocks regarding the simplex SPI bus on the Mediatek CPU.

TPLink seems to have gone the same route and built a smart-plug with and Atheros CPU. Again this blog post is meant to enrich the notes I already brain dumped on twitter.

This module is designed to be a wifi controlled relay with metering, switching upto 10A according to specs. It achieves this by using x2 5A relays in parallel. The main subsystems are:

  1. Power - Analog Devices/Linear Tech power AC-DC power IC. The footprint of this is an interesting variant of SOIC-8.
  2. Metering - This is done by the Maxim MAX71020A IC. Every electronics manufacturer worth its salt is creating metering ASIC's these days and I am excited about opportunities in making break-out boards and comparisons. TPLink seems to have bought up all the inventory of this particular Maxim IC and Maxim has a history of discontinuing low-margin lines the like MEMS accelerometers. I will keep an eye of the Poly-phase version which seems to be still in production (MAXQ3180). Overall this does not look good for the future of this particular smart-plug.
  3. Relays - x2 chunky 5v - 5A relays adorn the metering and CPU board. These provide the main functionality of the smart plug.
  4. Atheros/Qualcomm processor - This is the smarts in this smart-plug. Running standard open-wrt. The Maxim IC is of course on the SPI bus and other GPIO's are driving LED's , relays etc.
Overall the lack of supply of the Maxim IC does not bode well for the future of this Smart-plug. It may find fun alternative uses as an always on linux node.

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