Introduction
Our current flight computer is a PowerPC-based single board computer, specifically chosen because of a "Linux on POWER" grant from IBM that Dr. Massey received a few years back.
We chose the TQ-Components TQM5200 as our SBC because it had everything we needed:
- a 400 MHz Freescale MPC5200 PowerPC (that's a 603e core) with double precision FPU
- 64 MB SDRAM / 32 MB FLASH
- Lots of peripherals: USB 1.1, CAN, UARTS, PCI, ATA/IDE, SPI, etc.
It's a relatively small board at 80 x 60 mm, with an array of high density surfacemount connectors on the bottom. We've created a "carrier board" which adapts it for use in the AV3 system.
The carrier board is essentially a flight worthy version of TQ Component's STK5200, a giant, multi-purpose carrier board that breaks out the TQM5200 into essentially a PC motherboard (includes VGA, USB, keyboard and mouse, etc). That's good for prototyping, but it's too big and fragile for a rocket.
Flight Computer Carrier Board Requirements
- General
- Should cost (,150,500) $
- Should be a (,2,4) layer PCB
- Size
- Must be fit in the rocket (ID of ~ 13.33 cm)
- Must have a width of < 10.6 cm
- Should be as small as possible, (48,100,150) cm^2
- Should have components on both sides of PCB.
- Must be fit in the rocket (ID of ~ 13.33 cm)
- Rocketbus connector
- Must be mechanically and electrically robust, polarized, and locking.
- Must be easily removable except when in a "flight mode" when it must be locked.
- Must be as small as possible (TODO: numbers?)
- Must carry 8 electrical signals: Vb, ground, USB D+, USB D-, CAN H, CAN L, Aux 1, Aux 2.
- Must double up signals on connector for reliability: thus, requires >= 16 pins.
- Must handle power capabilities 20V @ 2A continuously on power pins.
- Must have horizontal and "up" and "down" right angle options for off-board connector.
- Telemetry connector
- Must provide a secondardy USB 2.0 full speed electrical connection (data and power) to the 802.11a USB adapter.
- Must have a polarized, locking connector.
- Must be able to turn the USB power on and off from MPC5200 (TODO: USB peripheral power switches? GPIO?).
- May have some indication of power on/off, data transfer.
- CompactFlash Card and Connector
- Must securely retain CF without data loss at (10,20,) g's of force at hundreds of Hz.
- May have fastener to hold connector to PCB.
- Must handle (1,8,) GB of storage.
- Must support the fastest MPC5200 ATA interface, UDMA mode 2 (33 MB/s).
- Must be polarized and locking connector.
- Should be easily removable when not in flight mode; Must have a locked down flight mode (although this can be added to a COTS part).
- Should be as small and lightweight as possible.
- May give visual indication for power, reads, and writes.
- Must securely retain CF without data loss at (10,20,) g's of force at hundreds of Hz.
- Power supply
- Must take an input voltage of (10,14.7,20) V.
- Must provide 3.3V +/- (,1,5)% for the TQM5200 and CF card.
- Must provide 5.0V +/- (,5,10)% for the USB 802.11a adapter.
- Must provide enough current, by at least a factor of 120%.
- 3.3V: 2.2 A * 120% = 2.64A so (2.64,3,) A.
- 5.0V: 500mA as per USB 2.0 specification so (0.5,1,) A.
- Must have a small footprint <= 9 cm&2.
- Must be thin, <= 1 cm.
- Must be light weight (TODO: numbers?).
- Must be able to survive (10,20,) g load.
- Must be > 70% efficient under all operating loads.
- Should have undervoltage cutoff and overcurrent cutoff (foldback is OK).
- May have reverse polarity protection; if not, we'll provide it.
- Other board features
- Must have transcievers as required: CAN, Ethernet, etc.
- Must have ESD suppression on all non-power pins.
- Should provide 3.3V primary lithium battery for MPC5200 RTC.
- Should have at least 8 LEDs and one RGB LED to indication rocket status.
- Should have all GPIO available for use via a breakout connector.
- If there's an audio out: Should have a small speaker for generating low quality (< 10 KHz BW) tones/voice.
- Should breakout VGA, I2C, JTAG and SPI to breakout connectors (VGA needs a corresponding breakout connector to VGA cable).
- May have an Ethernet breakout connector (and a corresponding breakout connector to ethernet cable).
- Ethernet breakout should include physical layer chips as necessary (e.g., magnetics).
Capstone Project
The FC carrier was handed over to a 2009-2010 capstone team for design, build and test. They successfully built and brought up the board, although not all features have been tested yet. Please see their project for the rest of the information on this board.
Completed Schematic
Here's a PDF of the schematic for handy reference. Otherwise, you can find the EAGLE CAD files in the avionics-cad repository.