Teardown: A Wi-Fi smart plug for home automation

-March 07, 2017

In November 2015, EDN published my teardown of Belkin's WeMo Switch; I followed it up with a hands-on analysis. These smart switches, once connected to my local network and from there to the Internet, are directly controllable by iOS and Android apps, convenient for when I've forgotten to turn off the coffee maker before leaving home. They're also controllable by my Amazon Echo, convenient for turning on and off my office light from my chair. But they're not the only game in town.

The TP-Link HS100 dissected here, which I bought on sale for $19.99 from Newegg back in April, is conceptually similar to the base Belkin WeMo Switch. And like the Belkin WeMo Insight Switch, the TP-Link HS110 upgrade adds energy monitoring capabilities.

I'll begin, as usual, with some external packaging shots:






Slide the top off the box and the first thing you see is the GPL notice. Good (open-source support) for you, TP-Link!



More generally, here's a shot of the included documentation stack:



Here’s a look at both sides of the quick-start guide:



Underneath the documentation stack is the switch itself and its backside:



And a closeup of the sticker found there:


As you can see, there's a seam along the sides, but no amount of "crowbar" (flat-head screwdriver) insertion and elbow grease convinced the two halves to part. I then realized there was a Philips head screw under the sticker, but removing it resulted in no ease-of-disassembly improvement.




Eventually, I replaced my wrist with a hammer, using it in conjunction with the screwdriver as a chisel to pop the two halves apart:




As with the Belkin WeMo Switch, the TP-Link HS100's power and digital subsystems are located in two separate PCBs. Here's the underside of the power PCB:


An easy lift-off exposes the bulk of its AC switching and AC-DC conversion guts. At top and bottom are the two six-terminal female connectors that mate it to the digital PCB below it:


Speaking of which, here's one side of the digital PCB, still ensconced in the enclosure:



And here's a closeup of one of the two six-pin extension bundles that electrically mate the two PCBs, presumably passing both DC power (from the power PCB) and switch control signaling (from the digital PCB):



Removing the digital PCB from the chassis allows us to take a closer look. This side is dominated by the Qualcomm Atheros AR9331 2.4 GHz Wi-Fi SoC. You can also see the PCB-embedded Wi-Fi antenna along the right side:



Flip the PCB over and the memory subsystem comes into view. On the right is a Zentel Electronics A3S56D40GTP 256 Mbit DDR SDRAM. And on the left is a GigaDevice 25Q32CVSIG 32 Mbit serial flash memory (that's a company I can't say that I've ever heard of before!).


Last but not least is a shot of the switches and other plastics underneath the digital PCB. Believe it or not, in spite of my prior "chiseling," the HS100 still worked (albeit with an integrity-compromised enclosure) when I put it back together!



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