Tracksoar is the smallest lightest open source APRS tracker available. It makes tracking weather balloons, model rockets, RC aircraft, and anything else that flies as easy as possible.
It is able to report location, altitude, temperature pressure and humidity to Internet once a minute for twelve hours with 2xAA batteries.
Because Tracksoar is open source you can also add your own modules to accommodate custom sensors to meet your specific requirements. By flying Tracksoar on a weather balloon you can reduce the required helium and balloon costs per launch and it can pay for itself with just 2 launches. No other APRS solution offers this level of integration, compact size, and customization.
Nice project, used also in Santa Barbara HackerSpace project to track baloons, as reported by the team:
We at the Santa barbara Hackerspace have been involved in around a dozen weather balloon launches. We have had a lot of fun with these launches and learned a lot, but found some issues. Most of the commercially available APRS trackers are closed source, large, and heavy, all of which add to the complexity of launching a balloon. So we decided to do something about it, and the Tracksoar was born. The tracksoar is designed to be flown under anything capable of lifting 60 grams, including balloons, RC planes, quad copters, or anything else that flies. The Tracksoar uses the 2 meter radio band (144.390MHz) which requires an amateur radio license to operate.
Since it is a real open source project, following this link you can find all the schematics, software and resources released.
If you like it, help them be funded on Kickstarter. Still 14 days to go!