Project Specification
Project Overview
Status: Rev-A schematic complete pending physical schematic cleanup and PCB implementation.
Drone-focused, ArduPilot-compatible flight controller using the STM32H753VIT6 as the only MCU. Rev-A retains the Hades-derived sensor/storage/interface set, uses external ESCs and external RF/GNSS, and keeps propulsion power distribution separate from protected avionics power.
Fixed Architecture
- One MCU only: STM32H753VIT6 (U1), LQFP-100.
- 4S LiPo: 12.0 V normal depleted point, 14.8 V nominal, 16.8 V fully charged.
- No onboard ESC bridges/gate drivers and no battery charging.
- Four raw VBAT/GND XT60 branches for external ESCs.
- One grouped 3-column x 4-row ESC signal header with DShot/PWM, signal ground, and telemetry per ESC.
- External u-blox MAX-M8C/MAX-M8-class GNSS over UART plus PPS.
- External ExpressLRS/CRSF receiver connector; no onboard RF transceiver.
- One USB-C USB 2.0 device/service connector. USB VBUS is sensed only and cannot back-power the 5 V or battery rails.
- One compact U1-only SWD header.
- External-camera control only; no analog/digital video passthrough.
Functional Blocks
- Power Input/PDB: J3 battery input, J4-J7 raw ESC branches, TVS, TPS26630 protected avionics branch, external blocking MOSFET.
- 5V/3V3: LMR33640 5 V buck, MP2332 3.3 V buck, MPQ20056 fixed 3.3 V low-noise sensor LDO.
- H753 Core: U1, HSE/LSE, reset/boot, decoupling, SWD.
- Sensors: corrected BMI088, ICM-42688-P, BMP390, IIS2MDC, TMP36.
- Storage: W25Q128 and microSD.
- USB/SWD, RF/CRSF, GNSS, CAN, ESC Signals, Camera, PMU.
Sensor Suite
- U7 BMI088 corrected project-local part, independent accel/gyro chip-selects and interrupts.
- U8 ICM-42688-P on SPI2 with interrupt.
- U9 BMP390 and U10 IIS2MDC on I2C1 with data-ready/interrupt signals.
- U14 TMP36 analog board-temperature sensor. The HadesMicro BOM has no standalone temperature device; its BMX055 only provides an internal die-temperature reading, so Rev-A uses a dedicated TMP36 implementation supported by ArduPilot analog temperature monitoring.
ESC Signal Interface
J18 is a 12-contact 2.54 mm header with a 3 x 4 physical grid, oriented as three columns by four ESC rows:
- ESC1: pin 1 signal, pin 5 GND, pin 9 telemetry.
- ESC2: pin 2 signal, pin 6 GND, pin 10 telemetry.
- ESC3: pin 3 signal, pin 7 GND, pin 11 telemetry.
- ESC4: pin 4 signal, pin 8 GND, pin 12 telemetry.
Signals use U1 TIM1_CH1..CH4 on PE9/PE11/PE13/PE14, each with 22 ohm source damping and a 100 kohm connector-side pull-down. Telemetry inputs use PE0/UART8_RX, PD9/USART3_RX, PD2/UART5_RX, and PE7/UART7_RX. Connector telemetry is 3.3 V logic only.
Camera Interface
J19 supports externally powered/control-capable still cameras and action cameras accepting a conventional active-low shutter input:
- Pin 1: regulated 5 V, budgeted to 500 mA maximum.
- Pin 2: GND.
- Pin 3: 5 V idle-high, BSS138 open-drain active-low trigger.
- Pin 4: reserved/no-connect; pins 5/6 are connector mechanical terminals.
U1 PE5/TIM15_CH1 drives the stage through 1 kohm; a 100 kohm gate pull-down ensures off at boot. No FPV video is routed through the controller.
PMU
Battery voltage
VBAT_RAW is divided by 102 kohm / 20 kohm and filtered before U1 PC0/ADC123_INP10.
- Scale: 6.10 V/V.
- 16.8 V battery -> 2.754 V ADC.
- Divider current at 16.8 V: 137.7 uA.
Battery current
The 80 A propulsion current does not pass through an onboard PCB shunt. J20 accepts paired Kelvin leads from an external 0.5 milliohm high-side shunt rated at least 5 W continuous. U13 INA240A2 provides 50 V/V gain and drives U1 PA0/ADC1_INP16 through an RC filter.
- Current scaling: 40 A/V.
- 80 A -> 40 mV shunt -> 2.00 V ADC and 3.2 W external shunt dissipation.
- 100 A -> 50 mV -> 2.50 V and 5.0 W.
- Nominal ADC span permits approximately 128 A before a 3.2 V practical output ceiling.
Power Safety Audit
- TPS26630 B_GATE maximum was checked against Q1 absolute maximum VGS; CSD19537Q3 is rated +/-20 V and is compatible with the controller's 14 V maximum gate drive.
- U6 is the fixed 3.3 V MPQ20056 variant. FB is tied to OUT as required by the fixed-output application; no adjustable divider is used.
- L1 saturation requirement is at least the LMR33640 6.2 A maximum current-limit envelope; the schematic requirement is 6.5 A.
- USB VBUS remains isolated from the system 5 V rail and is used only for ESD bias and VBUS sensing.
Power Limits
- GNSS allowance: 250 mA at 5 V.
- CRSF/ExpressLRS allowance: 500 mA at 5 V.
- CAN auxiliary allowance: 100 mA at 5 V.
- Camera allowance: 500 mA at 5 V.
- J18 provides no ESC auxiliary 5 V power.
- Raw propulsion-current capability remains a PCB-layout/current-density validation item.
Physical Design Constraints
- Final board direction is square and 8-layer.
- Keep switching loops and high-current copper away from sensors and analog PMU nets.
- Route USB D+/D- as 90 ohm differential with continuous reference.
- Place the external-shunt input filter and INA240 as a symmetric Kelvin measurement block.
- Do not claim 4 x 20 A branch capability until copper, vias, connector pads, temperature rise, and fault containment are validated.