Rocket OBC Design

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Block Diagram

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Project Specification

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Project Specification Project Overview
Rocket payload onboard computer (OBC), status: Draft/Review. The board accepts regulated 3.3 V and hosts an ESP32-S3 development module, navigation/environment sensors, GPS, CAN payload networking, and a buzzer driver.
Intended Use
Prototype rocket payload OBC installed on the existing 89.6 mm circular PCB with three existing mounting holes.
What the Device Should Do
  • Operate the Heltec WiFi Kit 32 V3 at 3.3 V logic.
  • Read MPU6050, BMP280, and GY-271-compatible modules over one shared I2C bus.
  • Receive NMEA GPS data over UART and support GPS configuration transmit.
  • Interface the MCU TWAI/CAN controller to an external HiLetgo SN65HVD230 module.
  • Distribute CAN and selected low-current 3.3 V/control signals through payload FFC con...

Power Budget

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Power Budget Scope
3.3 V OBC rail only. Excludes the 24 external payload boards and any high-current load beyond the FFC boundary.
Input and Protection Sizing
  • Upstream regulated 3.3 V source recommendation: at least 1.0 A continuous capability with low transient impedance; 1.5 A preferred margin.
  • Input connector and fuse/protection path: target ≥1 A continuous without excessive voltage drop.
  • Local energy storage: 10 uF bulk plus 100 nF high-frequency bypass at input, with additional local decoupling per external module interface.
  • Because the source is already 3.3 V, series protection must have low resistance; excessive fuse/PTC drop can violate ESP32 brownout margin.
FFC Power Limitation
The FFC 3.3 V pins are auxiliary low-current distribution only. This budget do...

Firmware Getting Started

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Firmware Getting Started
Final GPIO assignments will be populated from the completed schematic. Target framework: ESP-IDF with Heltec WiFi Kit 32 V3 board support.
Required peripherals
  • I2C master: MPU6050, BMP280, GY-271-compatible module interfaces.
  • GPIO interrupt: MPU6050 INT.
  • UART: GPS RX/TX crossed at the connector.
  • TWAI: CAN TX/RX to external SN65HVD230 module.
  • GPIO output: buzzer MOSFET gate.
Startup sequence
  1. Configure safe GPIO defaults; keep buzzer off.
  2. Initialize I2C and probe expected addresses.
  3. Configure IMU interrupt input.
  4. Initialize GPS UART.
  5. Initialize TWAI at the mission bus bit rate; termination is external.
  6. Start sensor acquisition and telemetry tasks.
Electrical notes

flux

Built and verified the complete Rocket Payload OBC schematic. It includes the 3.3 V input protection, WiFi Kit 32 V3 interface, MPU6050/BMP280/GY-271, NEO-6M GPS, SN65HVD230 CAN interface, four active FFC ports plus one DNP port, and MOSFET-driven buzzer. Final ERC review reports no open warnings or errors.
Open items
  • Library uses 10051922-1210EHLF, not the requested 10051922-1210ELF; contact orientation and footprint must be corrected before manufacturing.
  • Modules are represented by verified headers because exact breakout-board parts were unavailable.
  • PCB components are not placed; some footprints remain outside the circular outline.
  • Further execution is paused because no ACUs remain.
Suggested next steps
  1. Import/create the exact 10051922-1210ELF connector.
  2. Review the schematic and documented FFC pinout.
  3. Place components on the circular PCB.
  4. Configure CAN/power trace rules, then route and run DRC.
Fix FFC connector
Review FFC pinout
Place components
Check ERC/DRC
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Files

Schematic

Layout

3D View

Firmware Getting Started
Target: ESP-IDF on Heltec WiFi Kit 32 V3 (ESP32-S3). The exact Heltec board is represented by two 1x18 receptacle interfaces because the exact board part was unavailable.
GPIO / header mapping

Table

FunctionHeltec header interfaceESP32-S3 GPIO from PDF header mapNet
GPS UART RX (receives GPS TX)JH1 pin 5GPIO44 / U0RXDGPS_RX_ESP
GPS UART TX (drives GPS RX)JH1 pin 6GPIO43 / U0TXDGPS_TX_ESP
I2C SDAJH1 pin 12GPIO7I2C_SDA
I2C SCLJH1 pin 13GPIO6I2C_SCL
MPU6050 interruptJH1 pin 14GPIO5IMU_INT
Buzzer outputJH1 pin 15GPIO4BUZZER_GPIO
TWAI RXJH1 pin 16GPIO3CAN_RX
TWAI TXJH1 pin 17GPIO2CAN_TX
Payload/module enableJH1 pin 18GPIO1BUS_EN
External module headers
  • J7 MPU6050: 1=3V3, 2=GND, 3=SDA, 4=SCL; J13 pin 1=IMU_INT.
  • J2 BMP280: 1=3V3, 2=GND, 3=SDA, 4=SCL.
  • J3 GY-271: 1=3V3, 2=GND, 3=SDA, 4=SCL.
  • J4 GPS: 1=3V3, 2=GPS_RX input (MCU TX), 3=GPS_TX output (MCU RX), 4=GND.
  • J5 SN65HVD230 logic/power: 1=3V3, 2=GND, 3=CTX/CAN_TX, 4=CRX/CAN_RX.
  • J6 SN65HVD230 bus/aux: 1=CANH, 2=CANL, 3=GND, 4=BUS_EN if supported; otherwise leave module-side pin unconnected.
ESP-IDF initialization sketch
C
// GPIO numbers above are board-header mappings from the reference PDF.
i2c_master_bus_config_t i2c_cfg = { .sda_io_num = 7, .scl_io_num = 6, .clk_source = I2C_CLK_SRC_DEFAULT };
twai_general_config_t can_g = TWAI_GENERAL_CONFIG_DEFAULT(2, 3, TWAI_MODE_NORMAL);
// UART0 pins 43/44 may conflict with programming/logging; use a remapped UART controller if USB-CDC is preferred.
Startup sequence
  1. Set GPIO4 low and GPIO1 to the safe mission default.
  2. Initialize I2C at 100 or 400 kHz; probe sensor module addresses.
  3. Configure GPIO5 as interrupt input per MPU6050 module polarity.
  4. Initialize GPS UART with RX=44, TX=43 (commonly 9600 baud for NEO-6M modules).
  5. Initialize TWAI with TX=2, RX=3 and the mission bus bitrate; termination is external.
  6. Start sensor, navigation, telemetry, and buzzer tasks.
Do not enable extra board-level I2C pull-ups unless the external breakout pull-ups are removed/disabled; the OBC contains one 4.7 kΩ pair.

  • GPIO / header mapping

  • External module headers

  • ESP-IDF initialization sketch

  • Startup sequence