|Flight data encoded onto JT65 transmission|
Dave VE3KCL has used stripped-down versions of the U3S in a number of balloon flights including several that have circumnavigated the world. His balloons are simply mylar party balloons available just about anywhere at a very low price. He uses his own firmware loaded into the controller and powers it with tiny solar cells like these that weigh less than half a gram.
Hans mentions that he is now almost finished with the firmware for his balloon-optimized U3S (perhaps it should have a new name) and is hoping to make a few test flights in the next few weeks. Operational voltage requirements will be 0.5 to 5.5 volts. No word on current requirement but Dave powers his directly from "a few" of the solar cells mentioned above.
Evidently, there has been great interest in these tiny lightweight transmitters that can be put aloft with an equally tiny budget. The roadblock that stops most people has been the firmware which enables various telemetry data (battery voltage, temperature, altitude) to be sent via JT65. Now that that's being addressed, it may soon be possible for non-code writing hams to inexpensively send a party balloon across the ocean or around the world and track it via WSPR the entire way.