Bluebuzz

bluebuzz-rm2

Live project page & interactive schematic / PCB / 3D viewer: https://sequoia-hope.github.io/bluebuzz/ (full-window board viewer, renders & 3D gallery)

A Bluetooth vibrator controller: RP2350A + Raspberry Pi Radio Module 2 (the first board, an nRF52840 module, is abandoned and kept in archive/nrf52840/): Wi-Fi 4 and Bluetooth 5.2 Classic + LE (CYW43439), so the toy can be a Bluetooth A2DP audio sink (BTstack, in the Pico SDK) as well as a BLE-controlled device, and a USB audio device (TinyUSB) over its USB-C. 26 × 56.84 mm (squish_pcb.dxf with r = 10 mm lower tip offset inward by 2.0 mm), 6 layers. USB-C on the bottom tip is the only connector (the top dome is the RM2's RF keep-out); every other lead is an SMT pad row on the back.

Sensing is a 4-sensor diamond array of Infineon DPS368 barometers on the back (North, East, West, South), meant to be cast in soft elastomer after Tenzer, Jentoft & Howe, The Feel of MEMS Barometers (IEEE RAM 2014): rubber poured over the array and vacuum degassed so it fills the pressure ports, after which a load on the surface reads as pressure, linear to under 1 %, with 10 mN resolution. Each sensor is on SPI1 with its own chip select (CSB low at power-up selects SPI; the part has only two I2C addresses), on the switched 3.3 V rail, 100n beside it. An MP34DT05TR-A top-port digital PDM MEMS microphone (U40) sits on the front upper-right shoulder (PDM_CLK on GPIO29, PDM_DATA on GPIO28), and an LSM6DS3TR-C IMU on I2C1 sits on the back on the always-on rail, with both interrupts on GPIOs for wake-on-motion.

Same pipeline as the parent (python3 build.py here; the site stage rebuilds board b of the parent's pcbview.toml), with additions this denser board forced: route.py hands freerouting a tamed DSN (GND removed from its netlist since planes and pours carry it, the plane layers marked unroutable, its fixed GND copper turned into keepouts), lays the nets freerouting never closed by hand (the six QSPI lines, VBAT, PG_N, the PWM and SWD hops, the USB climb, LX, WL_CS, the RP2350's lone GND pin), draws every hand-laid bend at 45 degrees, and after routing puts a via in every GND pad it can (cutting freerouting's wires from under the ones it walled off; the finish stage re-closes them). The stackup is six layers (GND / signal / VSYS pour / GND inside) because four left 40-55 connections open. ROUTE_DRY=1 python3 scripts/route.py lays only the locked pre-routes, for a quick DRC of them.

What it is

Programming

Bridge the BOOT pad to the GND pad beside it while applying power (or call reset_usb_boot() from firmware) and the RP2350 enumerates as a UF2 drive on the USB-C. SWD on the same pad row for debugging. Firmware: Pico SDK with PICO_CYW43_SUPPORTED and a board file setting CYW43_DEFAULT_PIN_WL_DATA_OUT/_IN/_HOST_WAKE = 2 and CYW43_DEFAULT_PIN_WL_CLOCK = 3; BTstack's A2DP sink example is the starting point for sound-to-vibration; the DPS368s through spi1, one chip select at a time, in background mode at the rate the elastomer response needs (the paper sampled at 100 Hz per sensor).

Casting the array

Per the paper: a two-part room-temperature polyurethane (they used VytaFlex 20, E ≈ 280 kPa) poured over the back of the board to 4-10 mm over the sensors, then the mould placed in a vacuum chamber immediately so the air trapped in the sensor ports is pulled out and the rubber fills them; thinner rubber is more sensitive (1380 counts/N at 4 mm vs 165 at 10 mm for their sensor), thicker spreads the response. Solder the BAT and MOT leads before casting; the SWD pads under the radio can stay outside the cast area.

Before ordering

• The RM2 is not an LCSC part: Raspberry Pi approved resellers; consign it at JLCPCB or solder it by hand (castellated, 1.5 mm pitch).
• The RM2 footprint was drawn from the datasheet's figure 6 (release 7, 2026-02, docs/RM2-datasheet.pdf); check it against a module in hand.
• The DPS368 footprint is the LCSC/EasyEDA land for C3232508 (two columns of four 0.6 x 0.4 mm pads, 0.65 mm pitch, 1.45 mm apart); check it against Infineon's drawing. Pin 1 is the top-right pad.
• The DPS368 and the LSM6DS3TR-C are JLCPCB "extended" parts (a loading fee each per order). DPS368: $4.21 at 1-9, $3.60 at 10+ (2026-10).
• The flash is the 3 x 4 mm W25Q32JVUUIQ because the 2 x 3 mm 16 Mbit part had no stock; its KiCad land is by package name, check it against Winbond's drawing.
• No 3D models for the RM2 (not on LCSC) and the core inductor (LCSC land differs from KiCad's); the viewer draws boxes for them.