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MERGEN ABRA ROV Main Control Board - Project Specification
Purpose
Integrated main control PCB for an unmanned underwater vehicle (ROV). The board combines onboard electronics power conversion from a 48 V tether input, STM32-based control, Jetson Nano interface, sensor acquisition, ESC PWM signal interfaces, RS485/Ethernet/tether connectivity, test/debug access, and underwater-enclosure mechanical constraints.
Major Power Architecture Change
The previous internal 4S LiPo battery assumption is obsolete. The ROV is powered from a surface station through a shielded tether cable. There is no internal battery on the vehicle-side control board.
Removed assumptions:
  • Internal 4S LiPo battery.
  • XT60 battery input connector.
  • 13.0-13.5 V low-battery cutoff threshold.
  • 4S LiPo-specific buck-boost / SEPIC decision for the Jetson rail.
  • Reverse polarity protection using a P-MOSFET specifically for LiPo polarity protection.
Power Input
  • Source: external DC supply at surface station.
  • Transmission: shielded tether cable carrying power + Ethernet/RS485/control.
  • Tether length: approximately 20 m.
  • Recommended input voltage: 48 V DC.
  • Vehicle-side voltage must be calculated after tether cable cross-section and internal resistance are known.
  • Buck converter input range must be selected from the minimum vehicle-side tether voltage, not from nominal 48 V only.
Cable voltage-drop rule to apply later:
Vvehicle=Vsurface−Itether×RroundtripV_{vehicle}=V_{surface}-I_{tether}\times R_{roundtrip}
where round-trip resistance includes both supply and return conductors.
Onboard Power Conversion
Electronics rails on the control PCB:

Table

RailInputOutputMax CurrentLoad
Jetson Rail48 V tether12 V3 ANVIDIA Jetson Nano
System Rail48 V tether5 V2 ACamera, communication, connectors
Logic Rail48 V tether3.3 V1 ASTM32, sensors, logic
ESC rail:
  • 48 V to 12-16 V equivalent ESC rail conversion is handled on the PDB, not on this PCB.
  • ESC output voltage target, typically 12 V or 14.8 V, requires separate approval before any PDB/ESC rail design work.
  • This control PCB shall not implement the ESC power converter without explicit additional approval.
ESC PWM Architecture
  • ESC battery power does not pass through the PCB.
  • The PDB performs 48 V to ESC rail conversion and distributes ESC power.
  • This PCB only provides PWM signal and GND reference to the ESCs.
  • ESC connectors on PCB: 3-pin, GND / PWM / NC.
  • Each PWM line requires a 33 ohm series resistor.
  • ESC PWM connectors shall be aligned along one board edge.
Mechanical and Environmental Requirements
  • Preferred PCB envelope: <=100 mm x 160 mm; circular or rectangular to fit inside a PMMA cylindrical waterproof enclosure.
  • PCB stackup target: 4 layers: Top Copper / GND Plane / Power Plane / Bottom Copper.
  • Copper target: 2 oz outer layers, 1 oz inner layers.
  • PCB thickness: 1.6 mm.
  • Finish: ENIG.
  • Solder mask: blue or black, both sides.
  • Mounting: M3 mounting holes at corners/edges, connected to GND plane.
  • Connector strategy: external connector outputs aligned along one direction for enclosure-axis cable management.
  • Environment: vibration and humidity inside waterproof enclosure; conformal coating markings required around connector regions.
Functional Blocks
  1. 48 V Tether Input and Electronics Power
    • Tether power input connector/pads.
    • Input protection appropriate for 48 V DC tether system.
    • Tether voltage-drop validation after cable resistance is known.
    • 48 V input buck conversion to 12 V / 3 A, 5 V / 2 A, and 3.3 V / 1 A.
    • Independent STM32-controlled enable pin for each electronics rail.
    • Rail indicator LED and test point for each rail.
    • Output filtering: ferrite bead + bulk capacitor + bypass capacitor per rail.
  2. Jetson Nano Interface
    • Preferred connection: 2x20 pin header interface rather than SO-DIMM module socket.
    • Dedicated filtered 12 V / 3 A supply.
    • UART link to STM32 through 3.3 V-compatible interface.
    • 15-pin FFC/FPC connector for IMX219 MIPI CSI-2 camera.
    • Ethernet handled by Jetson; PCB provides magnetics-integrated RJ45 or tether cable pad.
    • Local bypass capacitor array close to Jetson power pins.
  3. STM32F407VGT MCU Core
    • STM32F407VGT in LQFP-100.
    • 8 MHz HSE crystal with two 18-22 pF load capacitors.
    • 10-pin Cortex SWD/JTAG debug header.
    • Reset button with 100 nF filter capacitor.
    • BOOT0 selectable through DIP switch or jumper, held low for normal boot.
    • Decoupling per STM32F4 hardware guidance: 100 nF on each VDD, bulk capacitor, VDDA filtering, VCAP capacitors.
    • Interfaces: UART1 to Jetson, I2C1/I2C2 sensor groups, 1-Wire DS18B20, ADC for current sensor, PWM outputs for ESC signals, emergency stop EXTI.
  4. Sensors
    • BNO055 IMU on I2C, SMD-mounted, decoupled locally, ADR/COM3 pulled low for 0x28 if used.
    • MS5837-30BA pressure sensor external via JST-SH 4-pin connector.
    • DS18B20 external via JST 3-pin connector.
    • ACS758 or alternative current sensor measures electronics input current only: Jetson + STM32 + sensors, excluding ESC line.
  5. Communication and Tether
    • RS485 using SP3485/MAX3485-class 3.3 V transceiver.
    • A/B differential line output to tether.
    • 120 ohm termination selectable via jumper.
    • TX enable from STM32 GPIO.
    • Ethernet output through RJ45 or tether pads; Ethernet managed by Jetson Nano.
    • Emergency stop isolated input through optocoupler from tether.
  6. Test and Marking
    • Test points for tether input, 12 V, 5 V, 3.3 V, UART TX/RX, I2C lines, and each PWM output.
    • Silkscreen: board version, team name MERGEN ABRA, production date, component orientation/value markings.
Open Approvals Required Before Schematic Design
  1. Surface power supply output voltage and maximum current capacity.
  2. Tether cable cross-section in mm² and internal resistance, or exact cable part number/datasheet.
  3. Minimum vehicle-side input voltage after 20 m tether voltage drop.
  4. ESC rail target voltage approval for PDB-side design: 12 V or 14.8 V.
  5. Final 48 V input buck converter IC family approval, e.g. LM5116, LTC3786, or equivalent alternatives.

    Purpose

    Major Power Architecture Change

    Power Input

    Onboard Power Conversion

    ESC PWM Architecture

    Mechanical and Environmental Requirements

    Functional Blocks

    Open Approvals Required Before Schematic Design

Documents

    MERGEN ABRA ROV Main Control Board - Project Specification

    Power Budget and Safety Notes

    Part Selection Notes

Assets

Assets are files uploaded to this project which can be used in various ways.

MERGEN ABRA ROV Main Control Board thumbnail
Integrated 4-layer ROV main control board for 48 V tether-powered underwater vehicle, with onboard 48 V to 12 V/5 V/3.3 V electronics power conversion, STM32F407 control, Jetson Nano interface, sensors, ESC PWM signal outputs, RS485/Ethernet tether interfaces, and conformal-coated underwater-enclosure constraints.

Properties

Pricing & Availability

Distributor

Qty 1

Arrow

$36.29–$39.48

Digi-Key

$9,546.14–$9,551.45

HQonline

$24.77–$25.01

LCSC

$42.94–$43.26

Mouser

$65.56–$65.68

TME

$17.46

Verical

$19.07–$51.62

Controls