Step 2: The Radio Communications
My last balloon used the XTend 900 radio module from Digi (http://www.sparkfun.com/products/9411) as the main communication system. This 1 watt, 900 MHz radio allowed me to keep communication with the payload for the entire flight while getting flight data updates once every 5 seconds. The XTend 900 can interface to the XCTU configuration software to change the serial data rate in a user friendly GUI way (http://www.digi.com/support/productdetl.jsp?pid=3352&osvid=57&s=316&tp=5&tp2=0).
On the PC side of things you need to connect the XTend 900 to the PC's USB port. The best way to accomplish that is to get the uUSB-MB5 USB to serial converter from 4D Systems (http://www.4dsystems.com.au/prod.php?id=18) and the XTend breakout board from Sparkfun (http://www.sparkfun.com/products/9596). Solder the breakout board onto the XTend 900 or buy the proper connector. Then solder wires from the uUSB-MB5 to the breakout board in this order:
-uUSB-MB5 RX to breakout DO
-uUSB-MB5 TX to breakout DI
-uUSB-MB5 GND to breakout GND
-uUSB-MB5 +5V to breakout VCC
-On the breakout board you will also need to solder a 10k resistor between SHDN and VCC.
The balloon payload is similar and you'll need another breakout board to make things easy. Solder between the GS407 and XTend 900 breakout board like so:
-GS407 RXD to breakout DO
-GS407 TXD to breakout DI
-GS407 GND to breakout GND
-GS407 VCC to breakout VCC
-On the breakout board you need to solder a 10k resistor between SHDN and VCC
We almost have a fully functional radio link between the GPS and PC. Keep going to the next step to fire it up!