The MT3329, made by MediaTek, is an ultra-compact GPS module containing built in patch antenna. The module outputs positional information over a 38400 baud UART using the NMEA-0183 protocol. This device will be used to record position data to be broadcast over the APRS network.
The initial configuration of the MT-3329 was with the VBACKUP pin unconnected and the LED cathode connected to the 3D-FIX pin. After connecting VBACKUP to +3.3V as directed in the datasheet, the device transmitted serial data at approximately 24kBaud. The solution to this problem was found in the DIYDrones Forum; which states that the 3D-FIX pin acts as an input on startup, and if read high starts the device in the 24kBaud mode. The pin must be low on startup for the device to start normally.
The MT-3329 was tested on a Spirent GSS6300 GPS simulator, which revealed that the MT-3329 cuts off serial data at just over 60k feet; indicating that the max altitude/velocity limit is an OR relation (stops working if either is exceeded). This is due to the ITAR, which states that sale of GPS receivers capable of reporting position above 60,000 feet and 1000 knots is restricted. This is primarily a concern in the use of GPS and APRS or similar trackers in high altitude balloon or high power rocketry applications.
Bill of Materials
|Part||Quantity||Unit Cost||Total Cost||Source|
|TC1185 3.3V LDO||1||$0.45||$0.45||Digi-Key|
|0603 Capacitor||3||$0.0096||$0.03||eBay - mib_instruments|
|0603 Resistor||3||$0.00294||$0.01||eBay - mib_instruments|
|0603 Green LED||1||$0.11||$0.11||Digi-Key|
|USB Micro B Connector||1||$0.87||$0.87||Digi-Key|
|Total Unit Cost||$31.69|
- MediaTek Inc., "Mediatek - 3329 Datasheet," 30 April 2010. [Online]. Available: https://docs.google.com/fileview?id=0B_dHj7E2weiiNmUzNDA3OTktNTNhNy00Y2Y5LTg0YTQtMzIyNzJhZmFiNjcy&hl=en. [Accessed 7 March 2012].
- "ITAR Category XV" [Online]. Available: http://www.oria.cornell.edu/export/keywords/categoryXV.htm. [Accessed 7 March 2012]