By Jim Griszbacher, informal member, Engineering Leader, Product Architect

In Part 1 of our Wyze Video Doorbell teardown, we delved into the housing of the device, with special attention to how their mechanical engineering team waterproofed the internal electronics. Waterproofing electronic devices is no easy task, and the Wyze team made some great design choices. In Part 2, we take a deep dive into the three PCBAs, which we’ve labeled as: main, IR + microphone, and power. We wrap up with some commentary on eight electronic assembly decisions that caught our attention. Teardowns teach us so much, and we can use them to glean ideas for products we’re helping develop. We had a lot of fun with this one.

Table of Contents

Electronics block diagram overview

Let’s take a look at the three PCBAs: Main, IR + Microphone, and power

Main PCBA frontside deep dive

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On the main PCBA itself, we can make some general observations.

The PCB itself is a standard 1.6-mm-thick multi-layer FR-4 PCB. We can’t be sure of the exact quantity of internal layers, though it’s likely to be between 6 and 8 given the PCBA complexity. The gold surface finish on the plated mounting holes and test points suggests it’s ENIG (electroless nickel immersion gold) finishing, which is relatively standard and provides excellent corrosion resistance and solderability.

With components mounted, we can see that the PCBA has top and bottom surface-mount components only. By avoiding through-hole components entirely, they’ve streamlined and simplified the production process.

The main PCBA features a number of interesting features and functions:

1. The main product controller, the Ingenic T31 1.5 GHz embedded image processor. The processor is a low-power dual-core processor designed for image and video processing with H.264/H.265 encoding directly onboard.

2. The external crystal oscillator for the Ingenic T31, with marking “CREC 24.000”. Given the 2.5 x 3.5 mm size and marking, a good guess is that this is the 24 MHz crystal from CREC.

3. An integrated 2.3-watt audio amplifier for the 8-ohm speaker, Awinic AW8735. The input to the audio amplifier is driven by the main processor. ****A curious move here is that the audio output is passed through the mezzanine connector to a speaker connector on the power PCBA. While this may have been necessary for assembly purposes, it’s not ideal from an electronic noise and EMC standpoint.

4. A 128 Mb NOR flash, Gigadevice GD25Q127C. This connects via SPI to the main processor.

5. This SO-8 package component only features the marking “6208 029” and wasn’t possible to identify. This could be additional external EEPROM or RAM.

6. The main PCBA 6-position FFC connector that connects to the IR PCBA and MEMS microphone.

7. Unmarked exposed test points on the PCB surface. This allows for easier debugging during development, or automated flashing and testing of firmware in a production test fixture. These pads are actually quite large at 2 mm diameter, where a more common size for these would be 1 mm.

8. Fiducial markings on the PCB surface used in the manufacturing process. These alignment features provide high accuracy references for equipment to apply solder paste, place components, and perform assembly inspection.

9. A high quantity of ceramic decoupling capacitors under the main image sensor. These are necessary to ensure stable operation of complex high speed digital electronics components, and proximity is key, which is why they’re directly opposite the sensor.

10. A mystery unpopulated connector, which looks like another FFC connector similar to item 6. This connects to pins 49–52 of the T31 processor, which are used for an external MMC/SD storage interface according to the datasheet. This means that the PCBA is likely used in a product that allows for storage of images and video to a removable SD card. The SD card socket PCBA would connect to this one via an FFC.

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Main PCBA backside deep dive

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Flipping the main PCBA to the backside, we find more key components and features:

11. A very curious feature! Instead of soldering the bottom ground pad of the main Ingenic T31 processor to the PCB, they have a plated through hole that exposes the pad to the air. Typically, the exposed pads of a large power-dissipating component would be soldered to the PCB itself to help with heat dissipation, but it’s possible the processor was actually heating the PCB directly too much. This heat may have caused thermal distortion in the image sensor (17), so they chose to decouple the processor heat entirely. This may help with image distortion, but the processor likely runs hotter.

12. The mezzanine-style board-to-board connector that connects to the power PCBA. It looks like this is a 20-position 0.5 mm pitch version that sits about 1.6 mm above the surface of the PCB.

13. Some leftover shmutz from tape and assembly glues.

14. A nicely labeled UART header for debugging purposes. It’s likely these are populated during development with a simple pin header, and then removed in production to save on cost.

15. This entire area provides general power management for the main PCBA and processor. It’s easy to identify, as we can see three large cubes that are the inductors used in DC-DC switching regulators. Five of the ICs in the area are SOT23-5 (sometimes called SOT-25) packaged components, common for low-cost integrated switching regulators. The package markings suggest they’re all either low drop-out regulators or DC-DC regulators from Torex Semiconductor. This cascaded configuration of power management components generates the various low voltages necessary for different semiconductor components, likely 1.5 V, 1.8 V, 2.5 V, 3.0 V, and so on.

16. The connector for the IR cut filter attached to the lens assembly.

17. The raw image sensor itself. With no marking whatsoever, we can’t know what this component actually is.

18. A curious sight for a dense product at such high production volumes: a separate PCBA for the 2.4 GHz Wi-Fi radio. This PCBA has castellated edges that are exposed conductive edges allowing it to be soldered directly to another PCB. The radio PCBA features Realtek RTL8189RTV, an 802.11 bgn single-band (2.4 GHz), SISO (single-input-single-output) radio. This radio IC connects to the Ingenic T31 via SDIO interface, common for high speed wireless radios.

These types of separate radio modules are typically chosen as they carry their own wireless ‘pre-certifications’ which are required by the FCC in the USA and similar agencies in other regions. Modules with “modular certification” are more expensive than implementing a radio yourself, but make sense for lower volume products where certification overhead may not make sense.

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IR + microphone PCBA features

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We can make some general observations on the IR PCBA**:**

• The IR PCB is a 1.0-mm-thick FR-4 PCB, likely to be between 2 and 4 layers, given the PCBA complexity. Unlike the main PCBA, we see exposed unplated copper on some component pads, indicating it isn’t ENIG finishing and is more susceptible to corrosion. This PCB could be considered HASL (hot air solder leveling) finished, where solder is flowed on any unplated surfaces to provide at least some level of corrosion resistance. HASL is an appropriate cost-saving measure on a simple PCBA like this.
• With components mounted, we see that the PCBA has top and bottom surface-mount components only. By avoiding through-hole components entirely, they’ve streamlined and simplified the production process.
• The IR PCBA features four surface-mount IR LEDs (1) to help with low-light performance, but they left space for two additional LEDs (2). It’s possible the designers weren’t sure how much light they would need and wanted some additional margin, but four IR LEDs was sufficient.
• The IR PCBA also features a single top-firing surface-mounted MEMS microphone (3), likely from the Knowles SiSonic family based on the top component markings (W016 A85A SOST). I’m not sure yet if this is a digital PDM or analog MEMs microphone. We need to see what it connects to on the main PCBA. There’s no ceramic decoupling capacitor located close to this component (or anywhere on this PCBA), which is generally recommended for supporting the voltage supply to MEMS microphones.
• There’s a significant hole in the center of the PCB (4). This is necessary given the product assembly, but I always try to avoid large mechanical holes in the middle of PCBs. We don’t just lose the PCB layers you can see, we also lose all of the internal layers of the PCB! Fortunately, this is a simple board so the impact is manageable.
• Lastly, there’s a 0.4 mm pitch, six-position flat flexible cable (FFC) connector (5) that connects back to the main PCBA. My guess is that the pinout of the connector and cable allocate two pins for the IR LED control, two pins for the MEMS microphone power, and two ins for the MEMS microphone data and signal. </aside>

Power PCBA frontside

The power PCB is a 1.0-mm-thick multi-layer FR-4 PCB that’s likely to be between 4 and 6 layers, given the PCBA complexity. The gold surface finish on the plated mounting holes and test points suggests it’s ENIG finishing.

With components mounted, we can see that the PCBA has top and bottom surface-mount components, with a through-hole electrolytic capacitor and a vertical through-hole USB micro connector.

The assembly process is streamlined using only surface-mount components, and then the USB connector and capacitor are hand soldered at the end of the process. The cutout of the PCB for the large capacitor helps to keep the assembly low profile, and the capacitor is mechanically supported by its own leads and the rear housing.

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Let’s take a look at some components and major features of the power PCBA:

1. Two surface-mounted pogo pins take in power from the metal contacts embedded in the rear housing.

2. Traditional doorbell power might be AC, or users may connect a DC power supply backward. To orient the power supply for the rest of the downstream electronics, we have a bridge rectifier, Good-Ark Semiconductor MB26S, a Schottky type that’s good for minimizing losses and reducing power dissipation in the form of heat.

3. The output of the bridge rectifier connects to the large 220 uF, 50 V rated through-hole electrolytic capacitor from Samxon, necessary for initial power supply filtering and support.

4. The output of the rectifier and capacitor circuit connect to a DC-DC switching regulator as identified by the large nearby inductor. The IC is a SOT-23-6 package with marking “HDCNA”, which I suspect is another Torex Semiconductor component. There’s a diode directly next to the IC with marking “K24”, likely Microdiode Semiconductor K24.

This diode tells me the switching regulator is an asynchronous buck, which uses an external diode to conduct current in the “off” time of the regulator as opposed to an explicitly controlled FET. Choosing an asynchronous regulator over a synchronous type may be done for cost, space and complexity reasons, but at the expense of efficiency.

5. The mezzanine connector mating side we saw on the main PCBA.

6. Several through-hole test points possibly used for debugging, development, or manufacturing test and flashing.

7. The debugging USB micro connector that is connected to the Ingenic T31 on the main PCBA via the mezzanine connector.

8. The 8-ohm loudspeaker connector, which is powered by the audio amplifier IC on the main PCBA via the mezzanine connector.

9. An alignment fiducial, like what we saw on the main PCBA and used in the manufacturing process by automated equipment.

10. We can see that the designers left some additional unpopulated locations for more capacitors on the DC-DC switching regulator (4). It’s possible that through testing they found additional capacitors weren’t necessary.

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Power PCBA backside

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Now let’s take a look at the backside of the power PCBA:

11. Six large, white, surface-mounted LEDs for illumination in low-light conditions.

12. The through-hole leads of the USB micro connector, which have been hand-soldered and have left behind quite a bit of flux residue. This residue is generally harmless where it is, but can have unexpected impacts if it were to accumulate on high speed RF traces.

13. The main doorbell button and associated backlighting. This type of surface-mounted dome switch typically has a long lifetime and high cycle counts if implemented correctly.

14. Another wireless radio, this one implemented “chip down” directly on the PCBA itself. The radio is a sub-1-GHz wireless microcontroller, Texas Instruments CC1310, used to communicate a button-press event wirelessly to the separate Wyze chime component. This wireless microcontroller communicates with the Ingenic T31 on the main PCBA via the mezzanine connector likely via a UART interface.

15. Sub-1-GHz radios require a number of passive external components for proper interfacing with the intended antennas. Different antenna types may require some amount of “biasing” or power from the radio, as well as DC-blocking capacitors to appropriately protect the radio itself. Most critically in this area is the RF matching network, which ensures that power transfer between the antenna and radio is optimized for the application and wireless frequency range used. This RF matching network varies with different antennas and can even be influenced by the amount of nearby metal in the form of other electronics that can cause interference.

16. The spring contact that interfaces with the flexible sub-1-GHz antenna adhered to the front housing. This is a single contact, implying that the external antenna is a monopole type that leverages the ground plane of the PCB itself as sort of an RF reference to “push off” from and radiate.

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