2005/06 Capstone Avionics Systems Team Project

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2005/06 Capstone Avionics Systems Team Project

• Project Title The Node Front End design for the
  PSAS LV2b Avionics System
• Members
• Sarah Bailey
• Jacob Davidson
• Glenn LeBrasseur
• Date 2006-2-3

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2005/06 Capstone Project Team

• Team members
• Sarah Bailey
• Jacob Davidson
• Glenn LeBrasseur
• Industry sponsor
• Andrew Greenberg
• Faculty advisor
• Mark Faust

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Who are our customers?

• Our single customer is the Portland State
  Aerospace Society (PSAS)
• PSAS is currently in the process of designing
  their fourth rocket or launch vehicle (LV) titled
  LV2b
• Our Capstone Team will produce the interface
  electronics of all of the LV's avionics systems

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Redesign of a network based open avionics system

• What is it?
• The common electronics which will control the
  interfacing of the various LV avionics systems
• Why is it needed?
• To ensure the integrity of the data the rocket
  generates and its safe recovery from a flight,
  all systems within the rocket must reliably
  interface with each other
• What needs to be done?
• Design and build the interface circuitry
• What will be produced?
• A two-layer PCB containing the electronics
  implementing the interface

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Who is the Portland State Aerospace Society
(PSAS)?

• Founded in 1997
• First US student chapter of the Aerospace and
  Electrical Systems Society (AESS) which is a
  technical society of the Institute of Electrical
  and Electronics Engineers (IEEE)
• As far as the group knows, they are the most
  advanced amateur rocket group in the world
• PSAS designs, builds and launch amateur rockets
  or launch vehicles (LV) into the lower atmosphere

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What is the purpose of PSAS and their objectives?

• Pioneering active guidance and open source
  software and hardware aerospace systems
• Long term goal
• Design, build and put a nanosatellite into
  Earth orbit

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What are the future plans for PSAS?

• Design their fourth rocket, LV2b, which will be a
  research platform for active guidance
• The rocket will consist of a network of nodes,
  each doing a specific function
• The following is the block diagram of the LV2a
  avionics system

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We are going to redesign the old node interface
of each node
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LV2b nodes

• MASTER NODE Flight Computer (FC)
• Amateur TV (ATV)
• Inertial Measurement Unit (IMU)
• Global Positioning System/Satellite (GPS)
• Environmental Sensors
• Magnetometer
• Recovery Node

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Where does the Capstone team fit into PSAS plans?

• We are in charge of designing the common
  electronics that run all of the avionics nodes
• Called a node front end, it includes
• 32-bit microcontroller
• Switching power supply
• Communication bus interface

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Block diagram of LV2b Node Front End
LV2b Avionics Node
Switching power supply
Application specific circuits (e.g. IMU, GPS)
32-bit microcontroller
Node Front End
Power bus
Comm bus
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What are the deliverables required of the
Capstone Team?

• Design of the node front end
• Schematic capture and PCB layout
• Design notes
• Front End prototype which includes
• Commercially built two-layer PCB
• Populated and tested components
• A white paper of the node front end design

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What is the Node Front End?(Example Recovery
Node)
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What is the Node Front End?

• Designed for PSAS
• Used with every Avionics Node
• Communications relay
• Local processor for sensor data
• Supplies power

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Node Front End Environment

• Rocket Environment
• -5o C to 40o C
• Intense vibration
• Acceleration up to 20 g
• EMI (10MHz to gt 2.4GHz)
• Test Environment
• frequent handling and transport
• frequent power and communications
  connect/disconnect

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Front End Constraints

• Should be lt 150
• Must be very robust
• Immune to EMI
• 1" x 2" in size
• lt 0.5" thick
• Power consumption lt 190mW
• Condition power bus (10-20V) to required voltages
  for the node

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Parts Constrains

• Parts should be
• surface mount
• able to be routed on a two-layer board
• connectors should lock down during flight
• Board may have a conformal coating
• Redundant external connectors

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Reproducibility

• COTS components
• open source or free software
• documentation
• PSAS wiki
• design notebook
• white paper

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Power Supply Requirements

• must condition 10V to 20V input to required node
  voltage
• gt 70 efficiency
• EMI from supply should not interfere with other
  systems
• external shutdown control
• undervoltage lockout
• overvoltage protection
• current limited

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Communications Bus Hard Requirements

• Must handle
• EMI
• shorts and opens on PHY layer
• acceleration and vibration
• Must prioritize messages
• System critical messages should be sent, even at
  the expense of non-critical messages
• bandwidth gt 1Mbps

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Communications Bus Soft Requirements

• Shoulds
• software handling retransmission
• Faulty nodes can be shut down by FC
• previous use in critical real-time systems
• easy interface to laptops
• node controllers flashed over bus
• existing bus protocol drivers

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CAN vs. USB

• differential bus
• 1Mbps
• CAN in cars
• message-by-message prioritization
• peer-to-peer
• automatic retransmission

• differential bus
• 12Mbps
• USB in medical devices
• bandwidth prioritization
• mastered bus
• depends on transfer type

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CAN vs. USB

• laptop interfaces through special hardware
• PSAS members wrote CAN drivers for PIC
• no CAN drivers for Linux or eCos

• laptop can directly plug into the bus
• local contacts who wrote USB drivers
• Linux has many USB drivers
• eCos has hardware-independent USB driver framework

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Microcontroller Requirements

• Needs
• 32-bit, gt 128K flash, gt 32K SRAM
• gt 10 MIPS (around 60 MIPS is the goal)
• OSS tools like gcc, gdb, or binutils
• open debugger protocol (e.g. JTAG)
• Usable packaging
• QFP, less than 144 pins (64 pins is ideal)
• BGA lt 32 pins (with commercial mounting)
• communication bus connection (USB or CAN)

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Microcontroller Requirements

• Wants
• multiple implementations from more than one
  manufacturer
• integer math ALU, 10 bit ADC, 3 PWM, watchdog
  timer, brown out reset
• reasonable voltage requirements (3.3V only or
  3.3/5V)
• existing open source RTOS, like eCos
• low power modes
• low cost