Cf mp3-player

Hardware (rev3)

KiCad 8 design files for the rev3 CF MP3 Player board, the board the firmware in this repository targets (BOARD_REV3=1, the default build). The silkscreen reads "CF Card MP3 Player V2.1"; the firmware and docs call this board rev3.

Top	Bottom (seen from below)

The schematic is also available as a PDF.

Files

The Gerbers match the fabricated rev3 boards. Compared with the set sent to fab on 2026-06-19, the only differences are the board's position on the sheet and one F.Cu copper-pour outline that moved by up to 0.12 mm when the zones were refilled. Tracks, pads, vias, mask, paste, silkscreen, outline and drill hits are unchanged.

Board: 62.8 x 61.7 mm, 4 layers, 1.6 mm, four M2 mounting holes.

Regenerating the outputs

Needs KiCad 8 (kicad-cli) and Python 3 with numpy, Pillow and PyMuPDF. The interactive BOM also needs the InteractiveHtmlBom plugin; the script skips it if the plugin is not installed.

python hardware/export_outputs.py

BOM notes

• ICs, connectors and switches carry Manufacturer and MPN fields in the schematic. Passives are listed by value and package only.
• Value notation: resistors 4.7K / 1M / 22R, capacitors 100nF / 10uF / 15pF.
• Do not populate: R35, an optional 0R link from the battery's third contact to the charger TS input; R36 (10K) is fitted instead.
• U5 is the RP2354B (RP2350B with 2 MB of flash in the package), so there is no external boot flash. U3 is the 8 MB PSRAM on QMI CS1, with C5 as its decoupling capacitor and R11 as its chip-select pull-up.
• The U4 front-end values (R9 47K, R39 3.9K, R29 1M) come from the bench notes. The fitted values are still to be confirmed; see docs/TONE_DECODE.md.
• Several footprints reference vendor 3D models (${KIPRJMOD}/*.step) that are not in this repository, so KiCad's 3D viewer leaves those parts out. cf_mp3_player.step contains the complete assembly.

TAC5212 support components vs. datasheet

Compared against the TAC5212 datasheet (SLASF23A, Figure 9-1 and the 9.4.2 layout example). The typical-application figure there is labelled "TAC5212 / TAC5112" because the two parts share a pinout.

The headset mic (jack sleeve, MIC_IN) is biased from MICBIAS through R30 (2.2K), AC-coupled into IN1P, and DC-coupled into IN2M so the firmware can read the remote buttons with the incremental ADC. With the default 5 kohm input impedance the 1 uF coupling capacitor puts the high-pass corner at about 32 Hz. Use low-voltage-coefficient (X7R) capacitors for C44 and C28.

AVDD runs at 3.3 V: the firmware leaves AVDD_MODE at its 3.3 V setting and programs VREF to 2.5 V, which the datasheet only allows with a 3.3 V AVDD. U7 is therefore the LP5912-3.3.

For a future spin: add 0.1 uF capacitors next to AVDD and DREG.

Board-level details the firmware depends on

All of these are in the design files:

• Headphone output wired single-ended and AC-coupled: OUT2P to the jack tip (left), OUT1P to ring1 (right), headphone return to board ground.
• Rotary encoder on GP15/GP14 with its centre push switch on GP46.
• U4 tone comparator front end dimensioned so GP7 receives the Apple remote's ultrasonic carrier (values in docs/TONE_DECODE.md; fit a TLV3201).
• Battery voltage sense through a /2 divider on GP47 (ADC7).
• TAC5212 DOUT used as the codec IRQ on GP9 (GP6 is not connected to it).

Pin map and codec routing: docs/HARDWARE.md. Known board-level limitations (cold power-on click, Microdrive read coupling, VBAT reference): docs/HARDWARE.md.