The electronics package that will be used for my Weather Balloon project is now complete. It consists of a Raspberry Pi Model B+, fitted with a Real Time Clock module and a camera. Power is supplied by a USB power ‘brick’ that provides 5 volts at 2 amps and should do that for 6 to 8 hours. An EA900TRS radio, a WiFi dongle, an 8gb USB memory stick and a GPS consisting of a USB FTDI board connected to a logic level converter then to a Ublox NEO6 GPS.
The total current consumption is about 450ma rising to about 750ma when the camera operates. The total weight is under 400gms and it will be packaged in a container constructed from foam board.
A python program reads the Serial Data stream from the EA900TRS radio. This consists of commands from the ground that can take single images, timelapse video and video files. The location and height can also be sent back to the ground from the balloon.
On the ground a laptop fitted with another EA900TRS radio runs a control programme written in Visual Basic.
This control programme allows the following:
Taking single pictures, Timelapse video and Videos. The interval and runtime for timelapse videos and runtime for videos can be altered from drop down lists.
GPS data showing location and height can be requested and it is a simple matter to input the latitude and longitude readings into Google Earth to show the location of the balloon.
A number of diagnostic data can be sent back from the balloon, the temperature of the EA900TRS, signal strength at the balloon and data from the radio on the PC, temperature, baud rate, channel number, Tx power output and signal strength.
A countdown timer is useful for determining if contact with the balloon has been lost. The balloon sends a response back to the ground when the requested action has been completed. If the signal is lost this response will not be received and the control panel will ‘lock up’ waiting for a signal that will never come. To get around this a BREAK button is provided, pressing this will stop the console looking for a response from the balloon.
A Sync button resets both the ground unit and the balloon to ensure the variables on both units match, this is used after contact has been lost, then regained. A ‘Find Me’ button can be used to confirm that communication exists between the balloon and ground.
The Raspberry Pi runs ‘header less’ and a WiFi Access Point is used in the field to allow the Raspberry Pi to be set up, and to allow an iPad to take pictures using Berrycam. The expected range for this is at least 100 feet.
All images are stored on an 8gb nano USB memory stick.
One example of the need for through testing occurred when I took the unit outside to test the range of the radios. The Raspberry Pi was set up using WiFi, then taken outside, everything went well until I returned inside. The Raspberry Pi did not reconnect to the WiFi and the only way to shut it down was to pull the power plug – not the best thing to do. The answer was to add another button (not shown in the image above) that shut the Pi down. The control panel sends a shutdown command, the Pi receives this and uses
os.system("sudo shutdown -h now")
to shutdown the Raspberry Pi.