Make the temperature sensor
The circuit cannot be simpler. We used the power unit with an Energiser lithium battery. Cold eats into the life of a battery so we used lithium batteries as they are the best to cope with this. The power unit is attached to the thermometer and number unit to display the temperature. We set this to Fahrenheit to give a greater range of temperatures displayed.
Circuit in box and insulation
Insulate the sensor from the cold.
The thick cardboard of the littleBits Space kit provides great insulation from the cold of near space, as does scrap packaging styrofoam. Hollow out the styrofoam to mount the circuit. Get as much of the battery in the Styrofoam by putting it lengthways through the Styrofoam. We put bubble wrap either end of the thermometer to limit the cold air getting into the rest of the box.
Record the temperature.
This is done with a small light weight video camera. The type we used was Catcam but there are others available. Turn it on before the balloon is launched and record the time it is turned on.
video image of numbers display with time stamp.
Check the temperature recordings and record thermometer height
Use another video camera to record the view of the Earth. This allows you to find the time after launch in which the balloon bursts and the payload lands. You also need to record the time you turn this camera on. You can then correlate it with the video from the thermometer and find the temperature at burst point. We used a Zlog 7 GPS data logger to track the altitude of the balloon. The data is time stamped so you can correlate the altitude and temperature using time. It also had an external temperature sensor so we could check the accuracy of the littleBits Space thermometer.
Zlog 7 GPs data logger in box
High altitude balloon launches need FAA permission. In the UK it is the CAA. After you get permission then wait for a nice day in your launch window. The Little Bits box needs to be attached to a suitable parachute and balloon to take it into the Stratosphere. We filled the balloon with helium to lift the balloon but, with some care, you can use hydrogen too. We forecast the balloon trajectory and launched it on a day when the balloon drifted over open countryside. The littleBits was recovered using a SPOT GPS tracker and GSM locator but you can use radio tracking devices as well.
Up, up, and away with the littleBits thermometer