2015-07-04 Long outside battery running test
On the on-board computer side, almost everyhting is ready, but the resilient-to-something-stop-working is still to do. I'm still considering using ChibiOS (the alternative being using various libraries with timeout in all the serial / I2C / SPI communications). But then, I would rather compile from the command line, and although having tried many (arscons, sonsduino, ino), I still haven't found a make or scons approach that allows the easy compilation of the zillions of files necessary.
I also would like to add another temperature sensor to get the temperature inside the capsule (so far there's only one thermometric probe). I'm considering either another BMP180 (luckily there are two I2C buses on the Teensy 3, so there would be no I2C bus addressing conflict), either the DHT11, but I'm not in a hurry to add yet another communication protocol to the wholething, my understanding being that the DHT 11 uses a kind of 1-wire bus. It might not be very fast for acquisition (and thus keep the MCU busy for too long), but I don't know, it has to be tested.
The tests on this Saturday gave three results.
I put the on-board computer, powered by a lithium battery on an old record player (that I got for 10€+port on ebay). The kind that is old enough to have a 16 RPM speed. Since the capsule of the balloon is always rotating and oscillating, I was worrying it would disturb the satellite signal (it doesn't, at least not noticeably).
The results are
- Although there are a lot of trees around my house, with a reasonably clear view of the sky, the rockblock had a close to 100% time transmission capability. I haven't been through the logs yet, but it could transmit almost all the time
- The rotation had no noticeable effet on the transmission
- Very importantly, the battery lost less than 0,1V on a 90 minutes session, in spite of the modem being a power hog when charging (but not when it has a satellite in sight). This gives a very high confidence in the computer capabilities to sustain a several hours mission.