Highway to Undercity

9/30/2025 - Looking for an SoC that has bulilt in USB controller

V1 had a few issues, one of them that there had to be a whole separate chip to convert from usb to uart for the esp32 (gen 1), and in general it is kinda hard to flash a first gen esp32.

But the problem is that from my research the only SoC that has Bluetooth audio, and wifi is the first gen esp. So v2 probably won't have Wi-Fi, so no Spotify/other streaming. Which is kinda sad, but I rather have a less feature packed project, then a project that is not in a working condition like v1.

So far I have landed on the STM32WBA65CI, it has ble 6.0 and audio support, its beefy, has plenty of io, and most importantly an integrated usb controller. Maybe for a next version I will add an esp32c3 has a Wi-Fi module, but first this has to work

Also, some other stuff that I have been thinking on changing/leaving for v2:

I will not use 0402 components, and other small components in general, it's just a pain to debug and work with, once I have a working prototype, I can do a version with small components
Simplify the power and battery systems, I won't use a power path and a fuel gauge chip, just a tp bms and a voltage divider for the battery percentage
I am leaving the DAC/AMP chip, and all the surrounding circuitry, except I'm using larger package sizes for the accompanying components

10/8/2025 - Realized that the nrf5340 exists

Realized that nrf has much better documentation, more examples and a better rtos. It has less ram than the stm32, but it is much more power efficient.

I have worked with the nrf52840 before, and it is almost the same. I'm just worried about routing the second row/layer of pins on the package

10/15/2025 - Found my dream BMS

I just found out that Nordic makes BMSs specially for the nrf5 series, it's called the npm1300, so they have full example schematics of the two working tougher!! It also has fuel gauge functionality, and is able to monitor every voltage in the system. It has two voltage regulators built in, that you can also control with i2c. It has native support for USB power negotiation. It also seems pretty easy to implement.

Most of my devlogs so far have been doing research😭

10/16/2025 - Started to redo schematic

Deleted a whole bunch of components. Added in the nrf5340 and all of its surrounding circuitry. Also added the npm1300, I'm so excited to use this bms btw (⁠≧⁠▽⁠≦⁠) removed the old BMS, some of the regulators, because the BMS has built in ones. IDK if I should use 1.8V logic or 3.3V logic though

Screenshot 2025-10-16 090028.png Screenshot 2025-10-16 090040.png

10/20/2025 9 PM - Reread the datasheet of my AMP/DAC chip

In v1 i used 1mm1mm power regulators for my audio chip, which were hell to debug/hand solder. SO this time I'm using almost the same regulator from TI, but in a 3mm3mm sot-23-5 footprint. I reread the datasheet of my audio chip, and realized that I don't actually need one of those regulators, so I'm now two regulators down, the other that I removed was my general 3.3v regulator, because the npm1300 has one built in.

Also, my hall effect sensor for my dial draws a lot of idle current, so I utilized one of the load switches of the npm1300(my beloved) to no give power to it when the device is in sleep mode

10/20/2025 11 PM - Finshed rough shematic