Power (rev H)
Sources
- USB-C (
J4) — VBUS into the charger / power-path IC; D+/D− to the Teensy USB pads. - LiPo (
J16) — VBAT / GND into BQ24075 (IC1).
The BQ24075 provides USB-friendly charging and power-path management (system rail while charging). Status LEDs D4 (red) / D5 (yellow) hang off charger status pins.
Main switch
EG2219 (S1) sits between the charger system output path and the board +5V distribution used by Teensy VIN-side power, encoder 5V, PAM8403, etc.
JP1 is a 3-pad solder jumper and it ships open. The center pad goes to the “on” side of S1. The switch common is the board +5V rail (Teensy VIN, the LDOs, encoder 5 V, PAM8403). With no bridge, sliding the switch does nothing and the rail stays dead.
Bridge one side only:
| Bridge | What runs |
|---|---|
| Center ↔ VYS (pad B, the end opposite the pin-1 mark) | Normal use. +5V comes from the BQ24075 system output. USB and the LiPo both feed the board through the charger, and S1 switches that rail. |
| Center ↔ VBUS (pad A, the pin-1 end) | USB only. +5V is raw USB 5 V, ahead of the charger output. Unplugging USB kills the rail even if a battery is connected. Useful while checking the board before you trust the charger path. |
Bridging both ends shorts USB 5 V to the charger output.
Regulated rails
| Regulator | Part | Rail |
|---|---|---|
U1, U7 | SPX3819 3.3V | +3.3V (logic / SD / parts of codec digital) |
U2 | SPX3819 1.8V | +1V8 (SGTL5000) |
| Codec analog | derived | +3.3VA net for SGTL analog supply |
Keep digital and analog returns as in the layout — don’t casually short +3.3V and +3.3VA plane strategy when editing copper.
Load switch (accessory / strip)
TPS22918 (U8):
- Input from +5V
- Enable from Teensy pin
36 - Switched output feeds
J9(with GND)
Firmware can gate power to an external WS2812 strip / accessory so it isn’t drawing when disabled.
Battery sense (firmware)
Firmware reads battery through A16 (pin 40) with a divider documented in toern.ino:
- 1M (
R15) top (VBAT → A16), 1.5M (R19) bottom (A16 → GND), plus smoothing cap - Nominal divider ratio:
1.5 / (1.0 + 1.5) = 0.600; firmware uses calibrated0.595
See Firmware pin map for the ADC constants.
Speaker amp
PAM8403 (U13) runs from +5V, takes analog feed from the audio path, and drives J10. Shutdown / control ties into Teensy GPIO (net 30_CRX3 on the enable-related pin in the PCB netlist).
Power-off and storage
S1 cuts the supply directly. Firmware cannot perform a shutdown save after that cut. Save to a numbered PATT slot before switching off; autosave is a separate pause/sample-load checkpoint with a five-second cooldown.