2015-05-23 More on the pressure sensor, battery level display, satellite modem status LED, decoupling capacitors
Problems with the computation of pressure / altitude are solved (debugged with a mix of comparing the results with the Arduino output and using Bosch release notes).
I've added 3 LEDs to get an idea of the battery level during the first (to come) field tests: 9 to 8V, 8 to 7, below 7 with a 0.1V hysteresis. All controlled and powered by the Teensy (and blinking to save some power).
I've also added a LED to show the status of the "net" pin of the satellite modem. My understanding is that the pin is on when the modem has a satellite in visibility, however it sometimes lit while the signal strength reported by the modem is zero ??? Not clear, but I like blinking LEDs anyway :-). I guess I can't draw much current from the modem pin, so the LED is powered on the main 5V through a MOSFET driven by the modem status pin.
Decoupling capacitors have been installed on every loads (470pF ceramic).