Created the Raspberry Pi 5 UPS Display HAT project requirements and power budget, targeting instantaneous active power-path switchover, a stable 5.1 V/6 A rail, and 4–6 hours from a 60–90 Wh protected external battery.
Open items
The schematic build finished in the executor, but I could not inspect or independently verify it because no ACUs remain.
ERC, component ratings, display GPIO conflicts, and zero-reset transition behavior still require review.
Next steps
Add ACUs, then request a schematic verification pass.
Confirm the exact display model and battery-pack connector/thermistor pinout.
After the schematic is clean, proceed to PCB placement and high-current routing.
Received notification from "Raspberry Pi UPS HAT" that it finished — picking the work back up.
The executor reports the UPS HAT schematic build is complete, but I cannot reconcile or independently verify its output because no ACUs are currently available.
Remaining work: inspect the schematic, run ERC, verify 5.1 V/6 A ratings and seamless switchover, check Pi/display GPIO conflicts, and validate the external battery connector pinout. Add ACUs, then request “verify and finish the UPS HAT schematic.”
A thin 40-pin stacking UPS HAT for Raspberry Pi 5, installed between the Pi and a 3.5-inch 480x320 SPI display using an XPT2046 touch controller. The board keeps the Pi and display operating when external power is unplugged and reports battery state to Linux.
Intended Use
Portable Raspberry Pi 5 touchscreen computer for hobbyist use. External power normally comes from a USB-C PD-capable power bank or adapter; an external protected rechargeable battery pack provides seamless backup and 4–6 hours of operation.
What the Device Should Do
Pass all 40 Raspberry Pi GPIO header pins through to the display.
Supply a stable 5.1 V rail to the Pi and display without interruption during source changes.
Charge and power the system simultaneously when adequate USB-C PD input is available.
Continue from battery immediately when external input is unplugged.
Measure battery voltage/current/state of charge and expose percentage to the Pi.
Assert a low-battery GPIO warning so Linux can shut down safely.
Allow the Pi to command final power-off after shutdown.
Raspberry Pi standard 40-pin GPIO stacking interface.
Display-side 40-pin female stacking receptacle.
USB-C power input; no USB data required.
External protected battery connector with battery temperature-sense support where available.
Reserved Pi signals: I2C SDA/SCL plus one low-battery alert GPIO and one shutdown-complete/power-hold GPIO. Final GPIO numbers must avoid the display's SPI and touch assignments.
Power and Runtime Expectations
Runtime target: 4–6 hours under typical Pi 5 plus display use.
The design must tolerate unplugging either external power or the battery without resetting while the other valid source remains.
Battery percentage must be readable by Raspberry Pi OS.
Power Tree and Power Budget
Preliminary load budget
Table
Load
Typical
Design peak
Raspberry Pi 5
7–12 W
25 W
3.5-inch SPI display/touch
1–2 W
2.5 W
UPS electronics/losses
1–2 W
3 W
Total
9–16 W
30.5 W
The 5.1 V rail is provisionally sized for 6 A transient capability. At a representative 12 W average load, 4–6 hours requires 48–72 Wh delivered. Allowing conversion loss and reserve, the recommended external battery class is approximately 60–90 Wh. A protected 2-series-cell pack around 7.4 V nominal and 8–12 Ah is the initial assumption.
USB-C input should support at least 45 W PD; 60 W is preferred if simultaneous operation and useful-rate battery charging are required. A basic 5 V power bank is not guaranteed to run a Pi 5 at full load and charge the backup battery simultaneously.
Prefer a four-layer PCB for low-impedance 5 V and ground distribution.
Use readily sourced components with thermal and current margin.
High-current connectors and copper paths must be sized from the final power budget.
Firmware-Relevant Hardware Requirements
Linux-readable I2C fuel-gauge registers.
Alert interrupt for low state of charge.
External-power-present status.
Configurable shutdown threshold and delay.
A daemon should request OS shutdown on critical battery, then signal hardware to remove power after halt.
Physical Design Expectations
Thin HAT/interposer positioned between Raspberry Pi 5 and the display.
Standard Raspberry Pi 40-pin header alignment and mounting-hole compatibility where the display permits.
Power and battery connectors accessible from a board edge.
Keep high-current switching circuitry away from SPI/touch lines.
Important Design Decisions
Use an external protected battery rather than mounting cells on the HAT.
Use active power-path control rather than diode OR-ing to minimize voltage drop.
Preserve the complete 40-pin interface while reserving only non-conflicting GPIOs for UPS telemetry/control.
Design for Pi 5 peak power, not only light desktop use.
Assumptions
The display is GPIO-powered at 5 V and uses standard Raspberry Pi SPI plus XPT2046 touch signals.
Exact display GPIO assignments will be verified from its model documentation before assigning UPS control GPIOs.
The battery pack includes cell protection/BMS but relies on the HAT for compatible charging.
Battery chemistry is initially assumed to be a 2S lithium-ion pack; final pack pinout, thermistor, capacity, and charge limits must be confirmed before fabrication.