POWER PATH

Charging uses a TP4056 with the charge current set by two solder jumpers (BR1 and BR2): 100 mA, 355 mA, 700 mA, or 955 mA.

The board implements the P-ch MOSFET from the reference circuit in the Raspberry Pi Pico datasheet. While USB is connected, the MOSFET disconnects the battery from VSYS, so the Pico runs from USB while the battery charges at the same time. When USB is removed, the battery takes over and supplies VSYS.

VBUS is a shared node. Charging works through the USB-C port on this board or through the USB Micro-B port on the Pico itself. Only one of the two should be connected at a time.

SOFT POWER CONTROL

One tact switch drives the whole power sequence. Pressing it once turns the system on, which is a fixed hardware behavior. The Pico then holds POWER_KEEP to latch its own supply, and the button state is available to firmware on POWER_SW, so the action that enters sleep or shutdown is defined in software.

The onboard switch is all that is needed for normal use. As an option, the POWER_SW pads on the back are wired in parallel with it, for a panel mounted button in an enclosure. A 2 pin header can be soldered horizontally, or wires can be attached directly.

BATTERY PROTECTION

The board includes a battery protection circuit with over discharge, over current, and over charge protection.

Above that hardware layer, the firmware can shut the system down before the protection circuit cuts in. This leaves time to save data or close files, which the protection circuit alone cannot offer since it simply disconnects the cell.

INDICATORS

Red LED: charging in progress
Green LED: charge complete
White LED: 3V3 rail present, enabled by bridging BR3

BR3 is open by default. The 3V3 rail stays up during sleep, so the white LED would remain lit in that state, and continuous operation draws current that matters on battery. Bridging it is useful as a power indicator when sleep is not used, or as a quick check of the 3V3 rail during bring up.

PIN ASSIGNMENT

The wing occupies 9 positions aligned to the Pico right side header:

VBUS, VSYS, GND, 3V3_EN, 3V3, ADC_VREF (NC), GP28, AGND (NC), GP27

Seven pins are connected. ADC_VREF and AGND appear on the wing but are not connected to anything on the board.

GP28 carries POWER_SW and GP27 carries POWER_KEEP. Two GPIO are required in total. If the board is not mounted directly side by side, each of them can be assigned independently to a different pin in the library configuration.

FIRMWARE

pico_battery_op provides the power state machine, button handling, voltage monitoring, and the shutdown and sleep transitions. Both a Pico SDK version and an Arduino version are available. Application code runs on top of the library, so an existing Pico project can be given battery operation without restructuring it.

SPECIFICATIONS

Target: Raspberry Pi Pico and Pico 2 (Pico W and Pico 2 W are not supported)
Charger: TP4056, charge current selectable by solder jumpers
Protection: over discharge, over current, and over charge
Power path: P-ch MOSFET per the Pico datasheet reference circuit, so the Pico runs from USB while the battery charges
Charging input: USB-C on the board, or USB Micro-B on the Pico
Battery connector: JST-PH 2.0 mm, 2 pin, right angle
Battery: single cell LiPo or Li-ion, 3.7 V nominal, not included
Board size: 27.3 mm (L) x 21.5 mm (W) x 6.6 mm (H), including protruding parts

NOTES

Set the charge current to match the battery. A high setting with a small cell can overheat or damage it.

JST-PH battery wiring is not standardized across suppliers. Check the polarity marking on the board against the battery before connecting.

The castellated pads are not guaranteed as a connection method. Solder the 9 pin header into the through holes.