7 July 15

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This past week we received the balloon parachute and did some rough testing inside of Bergen by dropping the balloon with a 1.5Kg simulated payload (a textbook). The height of the drop was measured and the drop was timed. We were able to calculate the descent velocity to be ~3.8m/s. This will be sufficient for the payload to survive hitting the ground, but not too slow that we will end with what is reffered to as a "floater": a balloon that takes too long to descend and will end up either in Canada or the Ocean due to the jetstream. You can use the Oxford Calculator to see this by entering a sufficiently low descent rate (0.1m/s really demonstrates this principle).

We have also activated the spot gps trackers and will keep a link in the links page that will allow anyone to track our balloon progress, we have set one up as a test here, however we are unsure how long the page will be valid.

Video Capture
Inorder to record the moment the balloon pops, we created a program in Python, temp_video.py, using OpenCV and the program to read temperature, temp.py, that activates a Logitech HD Pro Webcam attached to the Beagle Bone Black thru the USB port.  In order to run the camera, the BBB must be plugged into an external power supply.

The program created,  simply starts reading and recording video when the temperature increases over 300 Kelvin, which is just above room temperature. (Of course, in the balloon we want the camera recording when the balloon is at its apex, thus we will test for this when the Y-axis acceleration is 0.) You can test it by simply enclosing the thermistor with your thumb and forefinger.  The power supply for the sensor must use the 1.8 V ADC pin on the BBB which is P9_32, and ground to P9_34.  The circuit is set in series from VDD to a 1000 Ohm resistor to the thermistor to ground.  The voltage of the temperature sensor is connected to P9_37. See the yellow wire bellow.



We changed the clock speed of the BBB to 1000 MHz. (Check out this site for cpu frequency commands.)
cpufreq-set -f 1000
At this speed, the CPU usage is more than 95% when the video capture and recording kicks in.  At 300 MHz it is about 75%.  The programm also slows down considerably.  I suggest that if we are going to use this system to record the balloon popping, we use a separated BeagleBone Black and probably a separate power supply.




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