"hi,
Missionplanner secretly (shhhh!) outputs subsets of its internal data in response to html requests, in JSON. Take a look at http://127.0.0.1:56781/mavlink/ while Missionplanner is connected to a real plane or to a SITL aircraft. …"
"A mechanical solution may be simpler .... if your waterproof container is not rigid, the internal pressure will stay the same as outside. On a rigid container, you can drill a hole and glue on a loose piece of rubber balloon to achieve the same…"