Power Architecture
How power is distributed across an OpenSkyhawk cockpit. The firmware/hardware contracts cover the logic-side rails in detail; high-current actuator boards are not yet designed and are marked TBD below.
Distribution
A PC ATX power supply feeds the main bus with 12 V and 5 V, distributed between controller groups over Molex Mini-Fit Jr connectors. Each board generates its own 3.3 V locally — the 3.3 V rail is never distributed across the bus.
| Rail | Source | Used for |
|---|---|---|
| 12 V | ATX PSU, main bus | LED backlight strings; input to local 5 V buck on high-current boards |
| 5 V | ATX PSU, main bus | Input to the local 3.3 V regulator; stepper driver motor supply (VM) |
| 3.3 V | Generated on each board | STM32 / RP2040 logic, MCP23017, ADS1115, SN65HVD230 |
Local 3.3 V regulation
Every MCU and breakout board carries an AMS1117-3.3 LDO (SOT-223) that drops the bus 5 V to 3.3 V. The 1.7 V drop is acceptable at the boards' logic load (≤ ~175 mA). Local decoupling is required on every board: 100 nF + 10 µF per rail, placed close to each IC.
For the rare board that needs significant 5 V current, an AP63205WU switching buck (SOT-23-6) converts 12 V → 5 V on-board. This is not used on standard MCU or breakout boards — only on future high-5V-current boards.
Never use a linear regulator for 12 V → 5 V
The 12 V → 5 V step is done with a switching buck (AP63205WU) where needed, never an LDO — the drop would dissipate too much power. The AMS1117 LDO is only for the small 5 V → 3.3 V step.
Board power budget — logic + LED boards
Standard MCU and breakout boards are designed to stay within ≤ 500 mA at 12 V input:
| Rail | Typical | Max expected |
|---|---|---|
| 12 V → LEDs | 54–180 mA | ~360 mA (large panel) |
| 12 V → AP63205 input (if fitted) | ~100 mA | ~150 mA |
| Total 12 V per board | ~160–280 mA | ~510 mA (large-panel edge case) |
| 5 V → stepper driver VM | 15–30 mA | 50 mA |
| 3.3 V → STM32 + MCP23017 + CAN | ~125 mA | ~175 mA |
Across a full ~20-board cockpit that's roughly 2.3 A at 12 V — well under 10% of what a 500–600 W ATX supply delivers on its 12 V rail.
Cross-tier notes
- CAN transceiver (SN65HVD230) runs directly from the 3.3 V rail — no level shifter.
- RP2040 SimGateway is bus-powered from USB. If it's co-located with STM32 CAN hardware, share GND only — do not tie the RP2040 module's 3.3 V to the STM32 board's 3.3 V.
- Stepper driver motor supply (VM) runs from the 5 V rail. The driver is a DRV8833 dual H-bridge (four logic inputs per motor).
TBD — not yet specified
Marked TBD because it isn't in source material yet
- Actuator boards (solenoids, servos, large steppers) are not yet designed. Each will need its own power-budget analysis before PCB work — flyback protection, dedicated supply rails, and driver selection are all open. The established boundary is that logic + LED boards stay ≤ 500 mA at 12 V; actuator boards are sized to their specific loads and require separate design review.