Monday 25 July 2011

Microprize flight micro/altimeter.

We have been having some pretty good success with the flight computers we have been building.   They are based on the excellent leaflabs maple.
The Front of the board.  This shows the72MHz ARM Cortex M3 (STM32F103RB) with 20k ram and 128k flash.  It also shows the currently unpopulated voltage regulator.

The back of the board with the SD card socket, 200 g accelerometer (unpopulated in the pic) , BMP085 pressure sensor and two dual channel N-fets for ejection charges (4 channels total)

The board is only 18mm wide and as such will serve as a development board with the larger flight computer.  The larger flight computer has more sensors and a set of lower g accelerometers for dead reckoning in case the gps fails.

The GPS we are using is the venus module from sparkfun.  The breakout board just fits on the top of the board using header pins.  I considered using the module without the breakout board but I'm not that confident that I can design the high frequency bits of the circuit well (you have to make sure your antenna feed traces are 50 Ohm impedance etc)  Basically I decided to trust sparkfun on this one.  Plus it gave us one less thing to debug.

Obviously the 200 g accelerometer is pretty overkill and doesn't have much resolution in the range even rockets work in.  In fact the noise in its signal is about +-0.3 g  (one standard deviation) with a fair degree of oversampling and simple digital filtering.    This isn't too far from the chips stated RMS noise of 0.28g so I'm pretty happy with that.    The main reason for this is to test some launch techniques and to estimate shock loads.  (parachute openings etc.)

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