Intro: Barebones High-Altitude Balloon Cam
High-altitude ballooning, or HAB, involves sending a payload of cameras, scientific instruments, or other items on a journey into the stratosphere, strapped to a weather balloon. When the balloon bursts, a parachute brings the payload gently back down, where it (and your data/photos/freeze-dried food) can be recovered!
Most HAB systems are electronically complex, so we wanted to drastically simplify it. Our payload is only a smartphone designed to text its GPS location (for accurate recovery) and a Canon Powershot digital camera set to take a photo every few seconds until its memory is full.
Read on to see how we built it! Ours is far from the best design, and hasn't yet been field-tested, but the instruments work well enough. This is designed more as a starting point and a collection of tips.
Step 1: Instrumentation
The reason it's a balloon cam is, obviously, because there's a camera attached. We found a Canon Powershot A1000IS on eBay for $35 and installed CHDK on it.
CHDK is a nondestructive firmware hack that opens up all of a Canon Powershot camera's functionality. For our purposes, CHDK lets us put the camera in endless time-lapse mode under its own power, simulating a half-shutter press to focus and then snapping a photo at intervals of a few seconds. This means we can actually get photos from the balloon's journey!
The other essential piece of the equation is tracking and retrieval of the payload. To this end, we went with a simple (but slightly expensive) option: a Samsung Galaxy smartphone ($120 new on Amazon) with a temporary data plan from Walmart ($60).
With some clever Android programming, we made an app that, while running, texts the phone's current GPS coordinates to a designated number every five minutes. You can get the source code on GitHub.
The camera and phone are mounted in a custom-carved "book" of sorts, designed to fit snugly within the larger enclosure of the payload. This involved an hour or two of tracing, sculpting, and sanding the foam to fit the devices snugly, and then lining the inside with a few bits of electrical tape for extra grip.
Obviously the shapes of these mounts depend on which camera and phone you use--but the idea is to firmly hold both devices while only leaving room for the important part (the lens of the camera, protruding from the side of the box). The reason for the book shape is for easy access to both devices when assembling the payload--be sure to leave yourself room to reach the buttons on the camera, or activate your timelapse before you put it inside!
FAA regulations require unmanned balloons to include a radar reflector, which you can buy online if you want to be official. But there's a simpler way to include this: tape a layer of aluminum foil to the outside of the enclosure, shiny side out, and you'll mimic exactly what those expensive real reflectors are: a lot of shiny right angles. (The foil has the added bonus of making your payload look like a real space probe.)
Step 2: Lift and Drag
Based on the multitude of other high-altitude balloon projects shared online, we decided the tried-and-true Kaymont 600g weather balloon ($70) was our best bet.
For the return home (that is, a parachute, so that you don't drop a few expensive electronics at terminal velocity on someone's head from 90,000 feet), we went with another highly-recommended brand, Rocketman Parachutes. Depending on the weight of your payload, you may need a different chute--we went with a 4-footer ($45), rated for 3 pounds.
To tie it all together, we used 25 feet of neon orange paracord ($5), which was more than enough to work with. The inside fibers of this cord tend to splay out when the cord is cut; wrapping the ends in duct tape (a little like a shoelace) kept them in check.
While we're on the subject of cords, now is a good time to take ten seconds to learn a cool knot, the Eskimo Bowline. It's a very sturdy knot that makes a fixed-width loop at the end of your rope, perfect for attaching, say, a hypothetical weather balloon to the loop at the top of a hypothetical parachute.
Step 3: Enclosure
To build the actual structure of the payload, we bought a small rigid foam project board from Home Depot for around $6. If you have room in your vehicle and a little extra cash, it's much more cost-effective to buy a full 4'x8' sheet, but you'll want a reason to use it after this project--we didn't quite use all of our 2'x2' board.
We cut and assembled a rudimentary box using a utility knife (I recommend using one with a blade that extends out at least an inch; ours didn't quite make the cut all the way through our board, although snapping the foam along the score worked just fine) and duct tape. Be generous with the duct tape--it's fairly lightweight, and when you start making rough edges on your foam board, gluing securely gets to be a pain.
Step 4: Launch and Recovery
Be sure to notify your local air-traffic authorities well in advance. The same FAA regulations mentioned before also govern how heavy your payload can be and what kinds of documentation you need in order to launch. In our case, we didn't have an exact location pinned down the night before, so we were forced to postpone--precise coordinates are required in order for authorities to ensure you don't send a few hundred dollars' worth of electronics and paracord into a jet intake at 35,000 feet.
Do some research into how to safely fill and tie off a weather balloon; it's not as straightforward as you might think.
When we finally end up launching our balloon, this will be updated with the results! Good luck.