Teardown: Zigbee-controlled LED light bulb

Article By : Brian Dipert

A Zigbee-enhanced LED light bulb yielded plenty of interesting design surprises, but didn't give them up easily.

My house is Alexa-enhanced, with Amazon Echos, Echo Dots, and an Echo Tap scattered throughout. When I saw the second-generation Echo redesign for the first time, I was pretty underwhelmed by its comparative appearance; I guess I’m more of a “metal” (vs “fabric”) kind of guy. So, I decided to pick up a few first-generation spares, while they were still available, to put into archive storage for whenever the in-service units might die.

In doing so, I stumbled across the Echo Plus, a product variant I hadn’t heard of before. It looked just like the Echo, albeit with a slightly different sound signature that folks either marginally preferred or demurred. But here’s the key; in exchange for a slightly higher price tag, it included a built-in Zigbee device controller (subject to 10-100 meter range, although the protocol is mesh-based for repeater-enabled network range extension). As such, it claims to replace (for example) the standalone Bridge device normally required to link a conventional Echo to Philips’ Hue Zigbee-based LED lights (albeit with more limited functionality … according to reviews I’ve seen, the Echo Plus only supports elementary on/off functionality, not dimming, color-changing, or other Hue feature set enhancements handled by the Bridge).

What better way, I thought, to not only pick up a spare Echo but also do some hands-on Zigbee testing for the first time? Initially, I snagged a refurbished Echo Plus on sale (at the time) for $80.99, supplementing it with a standalone Zigbee-supportive 60W-equivalent LED light bulb for an additional $9.99. Shortly thereafter, brand new units went on sale for $99.99 (a close-out special, I accurately surmised at the time … the fabric-swathed second-generation Echo Plus is now the only option available for sale brand new), complete with a free Philips Hue bulb, so I got one of these, too.

With a spare LED light bulb now in my possession, a teardown became a feasible option. Specifically, what I’ll be dissecting today is Sengled’s model E11-G13, the Element Classic A19 “smart” bulb with 2700K soft white color temperature, currently sold on Amazon for $9.99. I’ll start out with some exterior packaging shots:

Inside you’ll find the bulb itself, accompanied by two internal support pieces of cardboard and a single business card-sized piece of documentation … that’s it:

Here’s the backside of that sliver of literature and a close-up of the bulb itself:

I fired up my heat gun to see if it might be able to cleanly separate the bulb’s translucent plastic globe from the more robust base … no dice, all it did was deform the globe:

A hacksaw, however, did the trick:

What’s this I see?

Once the bulb was partially dismembered, I was able to pull off the globe the rest of the way by hand. Inside, unsurprisingly, I found an LED array akin to that I’d seen last time I did a LED light bulb teardown:

Removing two Phillips head screws enabled me to pull the LED assembly right off, revealing the heat sink below it (that’s thermal grease i.e. paste, in case you weren’t already aware) and the two-prong connection to the remainder of the circuitry still hidden inside:

Stick a flat head screwdriver in that opening, carefully (so as to not damage what’s below) use it as a lever arm, and the heat sink pops right off:

Voila, the double-sided guts of the design. From last time, I knew it wasn’t going to be easy to get them out:

Look closely, however, and you’ll see a supplemental mini-PCB connector-tethered to the main one. I surmised, given the Faraday Cage on it, that it contained the Zigbee transceiver circuitry. And it was easy to remove:

The “cage match” was easily won revealing a Silicon Labs EM357 mesh networking SoC for Zigbee, along with support circuitry, inside:

The embedded antenna is faintly visible along the right edge of the PCB. This modular design approach is a smart move, because it allows for straightforward manufacture of both conventional base and (by adding the supplemental PCB on the assembly line) Zigbee-enhanced versions of the hardware.

Now for the primary PCB. Last time, I had to deal with what I at the time thought was quite a bit of white “glue.” How naïve I was, in retrospect …

After first trying unsuccessfully to yank the PCB out of the chassis from the front with a pair of pliers, then to twist off the screw thread/insulation/foot contact assembly with that same pair of pliers, I almost gave up … but one final frustration-fueled yank of the latter did the trick:

As was the case last time, the now-exposed “hot” and “neutral” wires seem to be contact-compressed to the base, not soldered to it.

Slowly and tediously, I was able to push the PCB out of the housing from the base end and equally slow-and-tedious application of the tweezers and other tools in my wife’s (ok … my) nail kit got rid of the white glue, exposing the transformer, passives, and other components underneath (this is certainly a fancier design than the one I encountered last time!):

Thoughts, readers? Sound off in the comments!

Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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