In First Year I worked with a single partner for my first project. We designed, built, and launched a small sensor package meant to go onto a high altitude weather balloon. The package had both humidity, pressure sensors, and a thermistor to passively measure temperature. They sent data to a PIC 12F1572 (our good old 8-pin PIC 12), and the data was output to a 433Mhz transmitter that was picked up by a ground station. The entire package was able to be powered by a single 9V LIon battery for over a week
Using the PIC 12 as the core, I set up the pressure sensor to work in conjunction with my partner's humidity sensor. They have to have their output boosted through a 5V Op Amp in order to get better resolution with their signals. The sensors took turns to communicate, since the PIC 12 is only capable processing one input pin at a time. The pressure data was used to measure the altitude as the balloon traveled. The calculations for that were done directly on the PIC, and output to the transmitter. In order to differentiate between the outputs of each sensor, we scaled the signals to create different tones, as well as outputting marker signals when the output was being switched. This allowed us to clearly decode and see the data we were receiving from the package.
I designed the PCB for both sensors and populating it when it arrived. After that we did some basic tests using what we had available. For the pressure sensor, I made a makeshift pressure chamber using a glass bottle and an electric pump. This was sufficient to demonstrate that the sensor did respond to changes, and we were able to calculate a fairly accurate pressure. I also built the enclosure pictured, in order to seal the board off from the elements. We were not permitted to use conformal coating, so a foam enclosure was required instead. After verification we successfully launched the package on a balloon which flew over the state and landed in a farm. We lost the payload for over a year before it was returned to us. To our surprise, we were able to just change the battery and the payload worked fine!