Smart hygrometers: Largely useful even with absent integrated visual monitors

What makes a market success? Is there a Swiss-made sensor inside? Or maybe a wrist strap? What happened to the basics: cost-effective reliable functionality? (And yes, get off my lawn, you kids!).

Back in late March, I detailed my experiences setting up TP-Link’s entry-level Tapo H100 smart IoT hub and wirelessly mating it with a Tapo T315 smart temperature and humidity monitor a few rooms over:

along with, for good measure, a Tapo T300 smart water leak sensor downstairs. The Tapo T315 was effective in several respects: proving that the two DREO humidifiers (one of them also “smart”) were functioning effectively, and that whatever humidity sensing technology was being harnessed in conjunction with my furnaces was not functioning effectively and should be ignored going forward.

Display-optional when the data’s already app-visible?

The Kindle-reminiscent 2.7” e-ink display built into the T315 was convenient for at-a-glance monitoring of both humidity and temperature…that said, truth be told, I can count on the fingers of one hand, without using any of them more than once (and maybe even some of them at all) how many times I’ve looked at it since setting it up. To wit, at the end of that late-March writeup, I noted:

I’ve also got a redundant Tapo H100 smart hub and T300 smart water leak sensor, both sitting on the shelf, queued up for teardown, along with a display-less sibling of the T315 hygrometer, the Tapo T310 Smart Temperature and Humidity Sensor.

The Tapo T300 is still sitting on my teardown pile, although I plan to get to it soon (I promise, barring any out-of-my-control delay factors, of course). The Tapo H100 was dissected toward the end of last month. And today, you get the Tapo T310. I’ll as usual start with outer box shots, as usual accompanied by a 0.75″/19.1 mm diameter U.S. penny for size comparison purposes:

Marketing hype? Reality? A bit of both?

The back panel notes that the sensor is “high-accuracy”. The product page further elaborates that it’s “Swiss-made”. What is this, a watch (analogy)?

Snark aside, Google AI Overview informs me that:

Switzerland is a global leader in high-precision humidity sensors, with key manufacturers like Sensirion, Novasina, and IST AG providing advanced capacitive and resistive sensors. These sensors are renowned for high accuracy, long-term stability, and are widely used in HVAC, medical, and industrial applications.

Assuming Gemini’s not hallucinating, I suppose that I could apologize to TP-Link’s marketeers at this point. But I’ll pass :

Open sesame:

Inside, as previously documented on the left-side box panel, is our patient:

along with various mounting, opening and literature bits, plus a wrist strap presumably for sensing-on-the-move purposes, or perhaps just as a fashion statement (???):

Dear friends, we shall never speak of the wrist strap again. Instead, let’s focus our attention on the device itself. Front:

Left side (note to self: must not draw reader attention to the hole for the wrist strap…):

Back, showcasing the translucent aqua bit of plastic intended for the owner to yank out in order to power up and otherwise activate the device:

Right side:

Top, revealing the ventilation and sensing vent (and another view of another wrist strap hole…arrggh…):

And bottom:

Mobile-adjacent in multiple ways

That cellphone SIM card bracket-reminiscent hole is our pathway inside. As you might have noticed from one of the earlier pictures, TP-Link generously included a SIM card bracket removal-reminiscent tool. I instead went “old school” via a nearby paper clip:

Mission accomplished, so far at least:

Next to depart is the battery, a not-terribly-common (therefore nice of TP-Link to bundle with the device from the get-go) CR2450:

And our last step before diving inside is to dispense (temporarily) with the aqua translucent plastic strip. I’m aspiring for this teardown to be non-destructive, so I’ll strive to hold onto it for reinstallation (followed by the battery) afterwards. I could, of course, keep the battery out of the compartment until I’m ready to activate, gift, donate or otherwise deal with it, but I’m more likely to lose the battery, so…

Another simple-therefore-low-cost consumer device

And here we go…

That wasn’t bad at all, and it might even still work after I reassemble it (he says, realizing that he’s just jinxed himself in doing so)!

Now to pop out the PCB:

Starting with the PCB backside, the battery terminals are already a known entity. Aside from the embedded antenna supporting TP-Link’s 900 MHz ISM band wireless proprietary protocol for bidirectional communication with the Tapo H100 smart IoT hub, there’s not much else notable to see (unless you’re into mode switches, such as the toward-the-bottom one labeled SW1, that is). Look back at the earlier pre-case-opening image of the exposed battery compartment and you’ll notice both the switch’s user-accessible hole and a larger manufacturer-tailored opening for test point TP12. And at the time, I guessed that the device at the top edge, PCB-labeled U5, was the temperature sensor (hold that thought).

Highly integrated

Things get more interesting, as they often do with teardowns like these, when you flip the PCB over (and no, I’m not referencing the comparative abundance of test points on this side):

Toward the top (vertically), and toward the center (horizontally) is the system’s “brains”, Cmsemicon’s BAT32G135GE 64 MHz (max) Arm Cortex-M0-based application processor. Below it are, at left, a Hefei Jingweite Electronics (JWT) 26 MHz crystal oscillator, along with an IC labeled as follows to its right:

300A
N997
423

The one (and only) semiconductor-related result emerging from a Google search on that particular three-phrase sequence was a link to the beefy user guide (PDF) for Texas Instruments’ MSP430 embedded controllers. I was initially skeptical re the relevance of that result, but I decided to press on to the product line overview page, where I saw included there the CC1 series, based on the Arm Cortex-M3, which supports “Sub-1 GHz dual-band” wireless. So…mebbe? If so (and regardless, actually), note that the PCB-embedded antenna is interestingly visible on this side of the PCB, too. Maybe so it reliably works in various orientations when the device is leashed to the owner’s wrist…oops…

An identity crisis

Below it, the conceptual teardown image I shared with you earlier had informed me, was the “Swiss-made” humidity sensor, strangely labeled D1 on the PCB and also strangely surrounded by foam (for protective reasons, I initially presumed, since its package was lid-less):

(I’m loving the 5x macro telephoto lens on the Google Pixel 10 smartphone I just got, which I’ll have more to share about in future writeups!)

How the ambient humidity could get through that foam to the sensor, though, was beyond me. Then I noticed the front-side hole in the case, at the same location as D1, and figured that was how. But then I looked at this stock image:

and realized thee things:

That hole in front was for an LED to shine though, actually
D1 was that LED, not a humidity sensor, and
The “temperature” sensor I’d previously noted on the PCB backside? I was half-right. It’s from Sensiron. And it does double-duty, sensing both temperature and humidity. Thereby even more completely explaining the topside vent proximity.

At this point, I could have just concluded that TP-Link’s marketing department has no clue how to draw conceptual images. But then I remembered TP-Link’s propensity for frequent hardware redesigns. And, giving the company the benefit of the doubt, I hit up the FCC certification page (2AXJ4T310) to have a look at the internal photos:

No such luck. The LED and humidity-and-temperature sensor seem to have always been in their current locations. TP-Link’s marketing department has no clue how to draw conceptual images.

With that, I’ll wrap up this writeup and turn it over to my readers for their thoughts in the comments. I’ll keep the device disassembled for a while after this writeup is published, in case you have any further questions, but eventually I’ll give reassembly-and-resurrection a shot.

—Brian Dipert is the associate editor, as well as a contributing editor, at EDN.