Teardown: Cutting into a multicolor LED light bulb

Article By : Brian Dipert

EDN has dissected a lot of LED (and CFL, for that matter) light bulbs of late, but they've all been white-only in their output. Let's add some color to the mix.

I’ve done teardowns on a number of LED light bulb “flavors” over the past several years: standard (see “Teardown: What killed this LED bulb?”), Zigbee-controlled (see “Teardown: Zigbee-controlled LED light bulb”), Wi-Fi augmented (see “Teardown: Wi-Fi LED light bulb”), and Bluetooth-enhanced versions (see “Teardown: Bluetooth-enhanced LED bulb”). I even recently dissected another non-incandescent approach: a compact fluorescent (CFL) bulb (see “Teardown: What caused these CFL bulbs to fail?”)!

One thing the above light bulbs all shared is that they output only “white” light—of varying color temperature, mind you, but still a pretty “monochrome” view of technology. This time I thought I’d change things up, going “Kodachrome” (as Paul Simon might say) with an LED light bulb that’s not only dimmable when controlled by an external app, but also multicolor. Meet Sengled’s Smart LED light bulb:

Sengled’s Smart LED light bulb

I’ve picked up a few of these of late, promotionally bundled with various Amazon “smart” devices. This most recent example came to me via a 2021 Prime Days promotion; for $24.99 I got both a current-generation Echo Dot (the spherical successor to the device I tore down a few months ago (see “Teardown: Amazon Echo Dot gets improved sonic performance”)) and the subject of this particular teardown. That’s a pretty smoking deal, if I do say myself, considering that the normal standalone prices are $49.99 (Echo Dot) and $14.99 (Sengled LED light bulb), for a grand total of $64.98 (plus tax and shipping, of course).

Note that, as prominently mentioned on the packaging, these bulbs are controllable only by the Amazon Echo ecosystem (voice commanded-devices plus smartphone and tablet apps):

Sengled Smart LED light bulb packaging

Note that as with the Zigbee precursor, a collection of these can collaboratively create an extended-range Bluetooth mesh network:

Sengled Smart LED light bulb packaging back

Sengled Smart LED light bulb packaging side

Apart from the bulb itself, the box’s content are pretty sparse, offering only a diminutive quick-start guide:

Sengled’s Smart LED light bulb quickstart guide

The star, of course, is our A19-form-factor patient, as-usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

Sengled’s Smart LED light bulb overview

followed by closeups of the bottom and side markings:

Sengled’s Smart LED light bulb bottom

Sengled’s Smart LED light bulb side 1

Sengled’s Smart LED light bulb 2

Sengled’s Smart LED light bulb side 3

I don’t know about you, but I still do a double take whenever I see a MAC address sticker on a light bulb! Other notable specs (IMHO) include 9W (per the product page on Amazon’s site; 8.7W to be exact) and claimed 60W/800 lumens incandescent equivalent, and that the bulb will not only output a range of user-configurable colors but also tunable “white” color temperatures ranging from 2000K to 6500K.

Time to dive in. As usual, per past experience, I turned to my hacksaw, which loosened the globe adhesive’s grip enough that I could pry it off with a flat-head (among other names) screwdriver acting as a lever arm:

Sengled’s Smart LED light bulb cut open

While the inside of the globe (see above) is unsurprisingly unremarkable, what illuminates it, on the other hand, is far more interesting:

Sengled’s Smart LED light bulb inside

Sengled’s Smart LED light bulb inside 2

Sengled’s Smart LED light bulb inside 3

Around the perimeter are 16 standard “white” LEDs of a type we’ve seen before with other bulbs. Inside that outer illumination ring is (unsurprisingly) another, comprising a smaller number (eight) of full RGB LED structures. Passives and two sets of connectors (presumably attached via pins to power and control circuitry deeper in the chassis) complete the picture. And, oh yeah, speaking of things connected to circuitry in “the depths,” you can’t miss that Bluetooth antenna sticking through and above the metal plate, can you?

Historically, getting that plate off in order to see what’s inside has sometimes been a struggle. This time it wasn’t bad, actually; I scraped off the remainder of the adhesive that had originally attached the globe to the chassis and then employed a smaller flat-head screwdriver to pry the plate away:

Here’s what the plate looks like standalone:

Unsurprisingly, it’s made of metal, to—along with the metal chassis—shield the environment (including the Bluetooth antenna) from the RF emissions of the analog and power circuitry inside the chassis:

To get any further, again from past experience, I needed to first use pliers to twist off the base:

This now left the tip of the PCB exposed (you can probably tell from the now-vacant solder point where the red through-hole wire still attached to the base originally went):

Pushing on the tip overcame the hold of the paste retaining the PCB in the chassis:

If you look inside the chassis now, you can see the brackets that originally held the PCB in place:

And, after removing the remaining attached glue, with the assistance of some isopropyl alcohol, here’s our first look at the LED light bulb circuitry “guts”:

The two ICs on the right side (shown at the top in the image) of the PCB underside shot are a bit of a mystery. One of them, labeled “BP1638,” is (I think) an LED on/off/dimming switch from a company called Bright Power Semiconductor. I can’t find a reference to the other—labeled “BP5711”—anywhere. My best guess is that it’s from the same supplier, and that in tandem they control the two concentric LED rings shown earlier. If anyone out there has a more informed idea, I’d welcome your thoughts in the comments!

The location of these two particular ICs matches up to the horizontal metal plate on the topside. Initially (and in retrospect, unwisely) I suspected it might be a Faraday Cage. In unsuccessfully trying to pry the top of it away (I think it’s actually a sturdily attached heatsink), I did discover one unanticipated surprise: this particular portion of the assemblage resides on a distinct mini-PCB:

I wasn’t completely off-base, however; there is a Faraday Cage in the design, attached to one side of the antenna board (review the earlier PCB overview photos and you’ll see it):

The photography isn’t impeccable, I realize, so you’ll have to take my word that the primary IC underneath is Telink Semiconductor’s TLSR8253, a Bluetooth v5 controller supporting Bluetooth Low Energy (BLE) as well as BLE Mesh topologies, along with 2.4-GHz proprietary protocols. As I’d suspected, the hardware implementation is conventional; the smart LED light bulb’s Amazon ecosystem-only “lock” is instead reinforced through both bulb- and system-side software.

And with that, having just crossed through 1,000 words, it’s time to conclude this particular project. As always, your thoughts are welcomed in the comments!

This article was originally published on EDN.

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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