• REV2 Circuit Results

    Sean Morton • 12/31/2025 at 18:23 • 0 comments

    Rev2 Results

    In addition to the power switching circuit issues I had with the Rev1 circuitboard, there were a few other issues I had that motivated a respin of the board relating to diagnostic capability:

    • LEDs for showing the status of the different voltage domains
    • I/O-controlled LEDs from the ESP32 
    • A way to probe the master clock signal
    • Ground references for the Saleae logic analyzer channels

    These would have been useful for the sake of determining the board state without having to attach scope probes or a USB-to-UART connection. 

    Although I was able to order bare boards and hand-solder them myself for a low cost, I found that the assembly time for each PCBA was a bit prohibitive. This led to me only soldering 2 assemblies out of the 5 bare boards I had received, and with each assembly I made, I had some concern about the reliability of my solder joints.

    For Rev2, I decided to get the boards fabricated at PCBWay! A few years ago, I had used PCBWay for the fabrication of bare boards alone for a different project, and had a good experience with their customer service. Bare PCBs take around 4-5 days to process, and the PCBAs take around 24-25 days. A huge thanks to PCBWay for sponsoring this project and covering the board and assembly costs. 

    One thing I really appreciated with PCBWay's assembly service was the level of support and communication I had with the fabrication and assembly teams. I had some issues with my PCB Gerber files, including design rules that did not properly enforce the minimum trace width that I intended to set. Once the board had passed engineering review and the PCBA was in review, the assembly team asked for clarification about the orientation of some polarized caps and diodes on the board (which my silkscreen didn't show) and to check an inconsistency in my BOM regarding which ESP32 version to use. Lacking an engineering team, I - as a solo designer - appreciated the feedback and communication, which was always polite, to keep the process running.


    In Rev2, in addition to implementing the diagnostic changes from REV1, I swapped some choices for some passive components and headers for ease of manufacturing. I also added a nifty logo and the load switch ICs mentioned earlier.


    When I received the circuitboards, one of the first pieces of behavior I had to debug was the power sequencing. When PVDD and DVDD of the TAS5711 aren’t sequenced with the correct timing, configuration of the TAS5711 fails, and I receive NACKs when I start writing to its registers over I2C. I found that the PVDD net was capped at 5.6V rather than matching the 18V input voltage, which was a little concerning until I read the datasheet for the TCKE905ANA,RF more thoroughly. It was also super useful to have up to 5 professionally-fabricated assemblies that I could use for this debugging, thanks to PCBWay’s sponsorship, rather than having only one or two hand soldered assemblies to work with.

    As it turns out, the TCKE905ANA,RF is designed for 5V nominal input voltage and clamps its output at 5.6-5.7V. A different available component that could work for an 18V input/output voltage is TCKE920NL,RF which has an overvoltage clamping voltage of 22.2V. This has a slightly different fault response from the TCKE905ANA,RF, but only the NL variant of the 20V eFuse IC was available on Digi-Key. To keep consistent fault behavior I may switch to the TCKE920NL,RF for both switching circuits, or use TCKE903NL,RF for the 3.3V switched circuit.

    More to come once I fix the power sequencing issues!

  • REV1 Circuit Results

    Sean Morton • 12/31/2025 at 18:12 • 0 comments

    Rev1 Results

    With the first rev of PCBAs, I bought the raw PCBs and the components separately, and performed the assembly of the boards in-house, with mixed results.

     

    I did all the soldering, starting with the SMD components with no-mess solder paste and a heat gun, and ending with the through-hole components. Note the red wire connecting from a 6-pin SMD package to a larger 8-pin SMD footprint in the PCB. This was because I had changed the NMOS component in my KiCAD schematic without updating the layout.

    One of the main articles that didn’t work well on the first rev was the PVDD (18V) power switching circuit. When 3V3 was supplied to the gate of the NMOS FET, the intent was that V_sg of the PMOS FET would reach 18V, and allow current to flow from source to drain. When I switched on the gate, I only ever measured 0V between the PVDD net and GND. I didn’t get to debug why this was before the circuitboard failed due to a short circuit while debugging.

  • Design Rationale and Selection

    Sean Morton • 12/31/2025 at 18:09 • 0 comments

    Design Rationale and Selection

    For this design project, I wanted to produce a Bluetooth speaker capable of projecting audio to a medium-sized room in my parents’ house, in a package roughly 8” x 4” x 4” that can be powered externally (with battery considerations being something for a later iteration of the project). When defining the circuitry needed for this project, I wanted to locate the following components:

    1. A microcontroller with a wireless data transmission module
    2. An RF receiver and transmitter module
    3. A speaker
    4. An audio amplifier IC
    5. A power switching circuit for sequencing of different power domains

    For the first two components, I knew that the ESP32 series of modules would fulfill most of my requirements with minimal fuss. At first I had chosen the ESP32-C6-WROOM-1-N8 module, but I soon found a problem with this: this module was designed for circuits that use Bluetooth Low Energy (BLE), not Bluetooth Classic. Bluetooth Classic is the high-bandwidth version used in audio applications, and has many more examples written of how to use in audio applications with the ESP32, so I changed my microcontroller selection to the ESP32-WROOM-32E-N8 midway through the hardware design.

    Speakers aren’t something I knew much about before this project, but I gathered that three important criteria to use for filtering were low-end resonant frequency, sensitivity, and audible frequency range. With my novice understanding, I filtered on Digi-Key for speakers with a resonant frequency below 200Hz, a good frequency response from ~20Hz to 20kHz, which are in-stock, have a datasheet available on Digi-Key, and cost less than $20/unit at low quantities. (link to search filters). I ended up going with the PUI AS07808AS-R (Fs = 120Hz) for the first prototype, which has a 82dB sensitivity and a frequency range from 60Hz - 40kHz. Some time after the first prototype I had a call with PUI engineers to review my design choices; in this call, they recommended the PUI AS11508AR-R (Fs = 80Hz) for its better low-end frequency response, which has an 84dB sensitivity and a frequency range from 80Hz - 15kHz.

    I then looked at amplifiers that could power this speaker. I wanted to make sure that the amplifier had an I2S interface for digital audio that would allow for abstraction of the microcontroller-to-amplifier interface, the capability to drive a 8Ohm load at a rated power of 15W, and a leaded SMD package (SOIC, TSSOP, QFP e.g.) to enable for easy hand-soldering and probing (link to search filters). I decided to use the TAS5711PHPR amplifier by TI, which met my requirements and was relatively cheap. The speaker has a rated power of 15W and a max power of 30W, whereas the amplifier has a power capability of 20W in the bridge-tied load configuration. This leaves no margin, but I don’t intend to operate the speaker at >15W due to its purpose as a relatively low-power, medium-volume speaker for use in quiet medium-sized rooms. The TAS5731M and TAS5713 ICs also meet the requirements, but have slightly higher power capabilities and compatible pinouts with the TAS5711. In the event that I need a higher power output from the amplifier, I’d evaluate one of those drop-in alternatives first.

    In order to drive an 8 Ohm load at the 15-30W range, it seemed most fitting to use an 18V nominal supply range for the PVDD net of the amplifier. I looked for off-board  AC-to-DC power supplies with a >20W power output capability (link to selection filters) and chose the following Mean Well part: GST25U18-P1J. Looking back at the search filters now, I’m not entirely sure why I bought the 25W version instead of the 36W version of this power supply. Maybe it came down to which parts were in stock at the time.

    The last major component that required some in-depth design decision was power switching to the PVDD and DVDD domains of the amplifier. I wanted to choose a load switch with some overcurrent protection and the ability to be switched from a microcontroller’s...

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