Propulsion Testing PCB

This project is part of the Duke AERO liquid propulsion test platform. To increase the reliability of the electrical system during test runs of the team's experimental liquid rocket engine, I am developing a PCB designed to perform analog signal sampling, power distribution, and valve control.

Problem Overview

The test platform is built around a network of pressurized tanks, tubing, valves, and sensors. Pressure transducers monitor system pressures up to 1000 PSI and output analog signals, which are captured and processed by an external measurement unit. The valves are actuated by servos that respond to external HIGH/LOW control signals.

Plumbing Diagram

Plumbing diagram. Image credit: Duke AERO.

Signal Sampling

The pressure transducers interface directly with the PCB, where they receive power and have their analog outputs routed to a connector for the external measurement unit.

  • Ground Referencing: Because the external unit uses differential inputs while the sensors are ground-referenced, ground is treated as S-, with 25 kΩ bias resistors pulling to an external COM reference.
  • ADC Integration: Two TLA2518 ADCs provide onboard sampling to validate sensor readings and help diagnose wiring issues between the PCB and the measurement unit.
Sampling Interface

Power Distribution

Buck converters regulate the fluctuating +12 V battery input into stable lower-voltage rails for the PCB.

  • Voltage Rails: Two independent AP63300 converters supply +6 V to separate servo banks, while an AP63205 converter generates the +5 V rail used by the ESP32-C3 and the pressure transducers.
  • Layout Optimization: The placement of the buck converters and their supporting components is optimized to minimize switching noise and reduce inductive coupling. High-current traces and copper pours are used to support elevated load currents and help dissipate heat generated by the converters.
Buck Schematic Buck PCB

Valve Control

The test platform's valves are actuated by servos controlled through a PCA9685 PWM driver, which provides eight independent output channels. To meet competition requirements, external trigger lines are also routed to the MCU, with an additional TLA2518 functioning as an I/O expander to capture these signals reliably.

Servo Interface

Future Plans

The PCB is currently in review, where the schematic and layout are under consideration prior to fabrication. Once manufactured, the board will undergo a validation process that includes:

  1. Power rail stability testing.
  2. Signal-integrity checks.
  3. Verification of all analog and digital interfaces.

Findings from this evaluation will guide any necessary design iterations before the PCB is fully integrated into the liquid propulsion test platform.

Full PCB