I have an old Canon Ixus camera which still functions. I had the idea of sending that out into the air with a helium balloon, along with a GPS tracker, so that I can retrieve the images it takes along the way. I believe the Pi could do that GPS transmission for me, with a GSM module.
The basics are these:
A store nearby sells 90cm diameter latex balloons filled with helium for about 30€. I calculated that a fully inflated balloon this big can carry approximately 500-600 grams of stuff. This balloon can reach about 10km on paper; however, if I only inflate it with half the helium gas (ie. 250L instead of 500L), there's a small chance it might fly higher before popping (I'm still working on that whether it's plausible). I might actually get two balloons filled with one's volume of helium. Obviously, I would need a permission from the local air traffic organization to release this, and make sure the winds are favourable. According to some articles, a meteorological balloon which flies as high as 35 km will travel about 200km, so if I can get to half of that or less, I should be looking at about 100km travel to get the stuff.
I've got some extra XPS insulation foam left over, so I could make a box out of it and stuff the camera and the Pi inside it. I suppose I would need to buy a clear acrylic sheet for a window. Anyone have any experience of photographing at 10+ km high through an acrylic sheet, will I get glares? The point here is that once that thing lands, it needs to float in case it splashes on water. As a parachute, I plan on using a plain old plastic bag! It can dangle behind the whole thing during ascend. Or will it freeze and break? Do I need to heat these things up at that altitude? At least the Pi won't need any heat sinks...
The camera would be set up to take a photo every 5 seconds or so. That way I should be able to fill about a 4Gb or 8Gb card within the 2-3 hours the balloon is up in the air, as long as the battery lasts (I need to check that it does...).
For the Pi, I already have an old 2000mA battery bank. I've got an Adafruit v3 GPS module with a backup battery (why does it have a backup battery if it's connected to a power Pi? It can't broadcast it's location so what does it need a battery for, unless it's able to store the GPS location data?). I need to buy a GSM module for the Pi and set it up to transmit the location data via SMS. If I can get a GSM module with 3G or faster, maybe I could even install another camera to the Pi and get it to transfer all the photos online directly to my ftp server? I've got some cheap camera for a Pi, but it's not a very high resolution one. Perhaps I should also invest in a barometric/altitude sensor module and store the flight data, just for giggles. Of course, with a limited battery bank, the less data crunch the better. I've got another battery bank of same size I could throw in there, maybe a good idea?
For weight calculation, the Canon Ixus weights about 128g with battery and card. The battery bank is about 75-100g. GPS and GSM module weight, don't know yet but shouldn't exceed 50g? A Pi board weights about 9-45g, so that's about 300g of equipment inside the foam case. The case itself... not sure how much that would weight, since I haven't carved it out yet. Wouldn't expect it to be too much? Overall, we should be within the lifting capability of the 90cm balloon, as long as it's fully inflated, or two balloons half-filled with helium.
My question to you good people at Raspberry Pi Forum is this: Which Pi should I put in? I've got a Zero, Pi1B+ and Pi2B to spare. Each cost me about 15€, so we're talking dirt cheap experiment here, as the Canon Ixus is 10 years old and has no value left. I know there's a weight difference between the boards, but that's about 10% of the whole mass. Still, less is better, right?
I suppose the total cost of the whole project comes to about 60-70€, so totally worth it. I don't want to invest too much on this, considering I might just lose it all. Has anyone ever tried this? Any tips on setting up the Pi? One thing is for sure, I need to disable HDMI, leds, pretty much everything else than what I need. Anything I've missed here, is this even possible?