On 26/09/2012, at 10:11 AM, damien.w...@gmail.com wrote:
> Brilliant stuff, Scott!
> Keen to hear more about the results of this scientific study.
> Care to tell us more details about how they work?
> Presumably, you have a gyro+accelerometer, microprocessor (Arduino?)
> and data-logger, radio transmitter, and some kind of battery that can
> withstand extremely low temperatures.
* AVR 2560, using Arduino Boot loader and some libraries
* LDO regulator, meaning we draw about 200uA while sleeping
* ARM CPU for Maths processing, only runs for about 5 minutes every 3 hours. Used a Beagle Bone due to memory requirements. This is the main part I would like to change. I think we could even do the maths on the AVR with a bit of effort.
* Iridium Satellite modem, very low power version that only send short messages (max size 340 bytes)
* Lithium batteries, derated to about 75% due to low temperature (-20 degrees)
* WDT - simple 555 timer, can't beat the simple solutions
* Kisteler accelerometer (thousands of $) and TI 24 bit ADC (with real 24 bits of data, very accurate, temperature compensated)
* POLOLU mini IMU for backup accel, direction, roll and pitch
* Temperature sensor (Dalas)
* Lots of FETs to control all the power circuits
* GPS for location and Time - automatically sleeps for approximate time, minus some safety margin (internal oscillator on AVR, very inaccurate and changes with temperature), then requires satellite. GPS has a small amount of power to improve start time, still within that 200uA and often will get a lock in 5 seconds and almost always less than 30 (50 seconds from cold).
* uSD cards for storage.
We built a motion platform, initially with a stepper, but moved to a simpler motor due to the noise from the stepper. In the end I was able to detect a 20 mm movement over 30 second - which is in the uG space!
Other Arduino test equipment we built:
* Arduino ISP
* Power monitor. Uses 24 bit DAC and calibrated low power shunt to measure power consumption over days
* Motor drivers - for motion platform
* Logic Analyser
* Lots of unit test - each hardware component was built on a shield
What I love about the little arduino boards hanging around and their popularity is that lots of problems are already solved and open license. E.g. it was quicker to grab an Arduino Mega to make a logic analyser, than wait for one to arrive, same for the ISP. I ordered one anyway, and have not even used it yet.