EPS Hardware

Guide to the Electrical Power System (EPS) on the BIRDS Platform

Estimated time to complete: 7 minutes

This guide provides practical insights and frequently asked questions (FAQs) related to the Electrical Power System (EPS) used in the BIRDS satellite platform. It is aimed at new EPS team members who are onboarding or seeking clarity on implementation and testing practices.

Table of Contents

System Overview

The EPS module is central to distributing regulated power to all satellite subsystems. It includes multiple DC-DC converters, fuses, analog-digital converters (ADCs), and microcontrollers that help manage power delivery and monitoring.

EPS typically interfaces with four microcontrollers (PICs):

  • MAIN PIC — core controller
  • COM PIC — communications controller
  • RESET PIC — responsible for satellite resets
  • START PIC — used at startup
  • Other components include: burn wires, MUXes, shared flash memories, and external interfaces (e.g., UART, SPI)

Power Line Configuration 

flowchart LR

  subgraph Power_Lines
    RAW[RAW POWER]
    DCDC1[DC/DC → 3.3V #1]
    DCDC2[DC/DC → 3.3V #2]
    DCDC3[DC/DC → 5.0V]
    DCDC4[DC/DC → Unreg #1]
    DCDC5[DC/DC → Unreg #2]
    RAW --> DCDC1 --> MAIN_PIC
    RAW --> DCDC2 --> COM_PIC
    RAW --> DCDC3 --> RESET_PIC
    RAW --> DCDC4 --> START_PIC
    RAW --> DCDC5 --> BURNER
  end

  subgraph OBC_Module
    MAIN_PIC[MAIN PIC]
    COM_PIC[COM PIC]
    RESET_PIC[RESET PIC]
    START_PIC[START PIC]
    MAIN_FM[MAIN FM]
    COM_FM[Shared COM FM]
    MSN_FM[Shared MSN FM]
    MUX1[MUX 1]
    MUX2[MUX 2]
  end

  MAIN_PIC -- SPI --> MUX1
  MUX1 -- SPI --> MAIN_FM

  COM_PIC -- SPI --> MUX2
  MUX2 -- SPI --> COM_FM

  MAIN_PIC -- UART --> COM_PIC
  MAIN_PIC -- UART --> RESET_PIC

The diagram above illustrates how RAW power is distributed to different voltage rails and used to power various microcontrollers and functional blocks.

Fuse Configurations and LED Indicators

  • Fuses are placed on each regulated power line to prevent damage during overcurrent conditions.
  • The LED indicators next to each fuse are useful for visually identifying which lines are live or broken.
  • Use a multimeter in continuity mode to test fuses and trace broken power lines.
  • Fuses are surface-mounted; replacement or bridging should be done cautiously.

Testing and Debugging Practices

Using External Power Supplies

  • During board-level testing, it is often better to use bench power supplies with current limiting features instead of satellite batteries.
  • Apply power to the RAW or VBAT pin with a regulated 8–12 V source.

Ground Station Test Environment

  • Ground Station programs are often developed using Visual Studio Community (free). The paid Professional version is not required.

RF Shielding for Command Testing

  • In some cases, a metal (aluminum) box is used to shield antennas during integration testing to simulate realistic RF conditions.

Sensor Behavior and I/O Behavior

Battery Temperature Sensor Behavior

  • The temperature sensor in the battery box outputs a voltage that decreases with increasing temperature.

  • The heater control works such that:

    • RD0 = 1 → heater ON
    • RD0 = 0 → heater OFF

Signal Interrupts on the FAB

  • For signals like DEPSW4 that seem interrupted at connectors like J15, this is intentional by design.
  • In many cases, jumper pins or manual soldering are added post-fabrication for continuity.

Tips from Past Missions

Communication Between COM PIC and Reset PIC

Although the circuit diagram shows a UART connection between COM PIC and Reset PIC, this is not functionally implemented in the firmware.

  • The UART connection exists on the schematic for debugging and flexibility, but was not needed for the flight version.
  • RB6 and RB7 on the Reset PIC are reserved for UART during development to send data directly to a PC for debugging, bypassing the Main PIC.

Software Update Limitations

How were software updates and patches handled for BIRDS satellites after launch? Software updates were not possible after launch due to hardware constraints. Therefore, robust testing was performed before launch to reduce the risk of in-orbit issues.

Additional Q&A

We continue to update this guide as new experiences are gained across missions.

If you have additional questions, please contact your EPS mentor or refer to the EPS debug manual.