This transmitter setup includes: One Arduino Uno board, one Ublox GPS board and one 433Mhz FSK transmitter board. Using the standard 433mhz license free frequency and Arduino Uno. Arduino Uno board($15 on Ebay): 1- Transmitter setup: GPS board: Ublox NEO6MV2 Module, this module have been tested to work above the 60,000 feet Cocom limit. This is a 3.3volts based board. This gps board(gps) have 4 points connections to the Arduino Uno(au): Ground(gps) -> Ground(au). 3.3volts(gps) -> 3.3volts(au). Tx gps board(gps) -> Digital pin 4(au). Rx gps board(gps) ->(voltage divisor) Digital pin 5(au). Ublox GPS board($20 on Ebay): For the voltage divisor connect a 10k resistor between ground and Rx in gps board and then a 4.7k( or 5k) resistor between Rx in gps board and digital pin 5 in au. This is to limit to 3.3 volts the voltage that will reach Rx in the gps board, each digital pin in the arduino is 5volts based. FSK 433MHZ Transmitter Module: This FSK transmitter board(tb) have 3 points connections to the Arduino Uno(au): 1- Ground(tb) -> Ground(au). 2- 5vols(tb) -> 5volts(au). 3- Data(tb) ->Digital pin 12(au). FSK Transmitter/Receiver boards($10 on Ebay): Using FSK modulation is a good way to eliminate noise in weak signals. Even when this is a very weak transmitter: 6dBm, about 4 mW, it have a very good range and is very reliable, you can always boost its output using a Transmitter Amplifier like this one: http://electronics-diy.com/product_details.php?pid=499. Emergency Release Commands: This Arduino code includes two emergency release modes: 1-Limiting Coordinate Rectangle: We defined 4 limiting Coordinates values, two latitudes and two longitudes. A MaxLatitude, MinLatitude, MaxLongitude and MinLongitude, this basically define a coordinate rectangle, we assume that the balloon is going to be launched from a point inside this rectangle, if at some point any boundary in this rectangle is reached then Digital pin 6 is set to HIGH. The idea is to use this to trigger a thermal wire and cut the line joining the parachute and balloon. This will allow you to do a emergency release in case that the balloon goes beyond a reasonable landing area. 2- Pressure Release valve: We defined a Maximal allowed Altitude, defined by default to be 27432 meters (90,000 feet), of course that can be changed. If the current altitude goes beyond this MaxAltitude then Digital pin 7 is set to HIGH. This will allow you to connect a trigger to this pin that will open a valve and release pressure from the Balloon, if the Balloon is still inside of the Limiting Coordinate Rectangle then this potentially will extend the time that the balloon will stay afloat without bursting. Connecting pins 6 and 7 is optional. Working Source Code for Transmitter: The code is based in the VirtualWire library created by Mike McCauley (
[email protected]). TransmitterGPS Code Possible extensions to this setup: 1- Add a Bluetooth board, similar to the one in the receiver setup, to communicate with another Bluetooth aware component in the payload, like an android phone, this will allow sending GPS updates to the second device and receive commands from that device. 2- Video Overlay: If your payload have a setup where you have a video camera and then a separate video recording device you can use a board similar to this one from Video Experimenter to overlay text and/or graphics into the video signal before recording it, or send it. You can also capture low res video frames and maybe you can send that in the signal payload.
