Sensors/GPS
GPS Receivers
We currently use and support two different GPS Receivers from u-blox.
uBlox LEA GPS Receiver
The Tiny uses the new LEA-4P from uBlox. It features their new Antaris-4 technology and uses uBlox's more efficient UBX binary protocol. This module is a surface mount package which is soldered directly onto the target board (Tiny in this case).
ublox LEA GPS Receiver
uBlox SAM-LS GPS Smart Antenna
The other boards use a stand alone module from u-blox called the SAM-LS. It is an integrated TIM-LP module with a ceramic patch antenna. This processor also runs on 4hz and is reprogrammed to run on UBX protocol. Both modules have proven reliable and robust. With battery back up they show hot starts of around a couple seconds. The LEA-LA processor weighs a couple grams, while the SAM-LS module with antenna and shielding weighs about 20grams.
ublox SAM-LS GPS Smart Antenna
This section should be rather short as the GPS receivers from Ublox are pretty much ready to go when you get them. Some things are different in protocol however so you will need to program them using Ublox's software.
Sourcing from u-blox
uBlox keeps tight control over the distribution of their products. They must be obtained DIRECTLY from their own reseller offices. These offices may not be available in your area, for example Canada does not have a reseller. Sample quantities can be obtained from uBlox but overnight or 2 day shipping is required which drives the cost up considerably. While it is a large hassle obtaining these devices, it is undoubtedly worth it. Check with project members to see if they have a few lying around first.
GPS & Control Boards
The autopilot hardware currently uses two different GPS receivers and are summarized below.
Tiny AP
This board is designed to have both the GPS receiver and antenna soldered directly to it. It accepts any receiver from the u-blox LEA. Keep in mind that if you are not using a GPS model with flash (LEA-LA) you will need to configure the AP to send boot commands to the GPS on start up. The programmable models include Flash EEPROM internally and save their configurations indefinitely.
Classix and Lite AP
These boards are configured to connect to an externally mounted u-blox SAM-LS module The SAM-LS runs at 3.3v(Lite uses a resistor bridge). The only suggestion here is to remove the case on bottom, and solder the 4 wires directly to the TIM GPS module(GND (pin 1) ,VCC (pin 2),TX (Pin 5),RX (pin 4)) u-blox has the pinout in the manual for the GPS.
1.2.1 AVR and RoboStix AP
This board requires a GPS board which includes a 3.3v regulator and a resistor bridge. The PCB files for this board are in the CVS under SAM-LS.
GPS configuration using U-Center
U-Center is a GPS evalutation software from Ublox. It allows you to graphically view the status of your GPS and to configure it. It's available for download at the Ublox web site. It is unfortunately only available for Windows.
In order to configure your module for use with your AP, you first need to connect it to your computer. Keep in mind that the Uart from the module is running at TTL level, not RS232. So you can either use a MAX232 or use a USB-serial adapter (TTL) such the pololu: http://www.pololu.com/products/pololu/0391/ or the sparkfun: http://www.sparkfun.com/commerce/product_info.php?products_id=199. Using these USB device has the additional advantage that you can use the 3.3V regulator that is built in to supply your GPS.
Once it's connected, start U-center, choose your com port from the pull down list under the connect button. Choose your baudrate from the pull down box right of the connect button.
Then you need to open the message window (menu View->messages view) to start the configuration process. Here's the list of steps that needs to be done:
1. Right Click on the NMEA Icon and choose disable child 2. Choose ubx->cfg->nav2 - set it to use Airborne 4G 3. Ubx->cfg->rate - change the period to 250ms 4. ubx->cfg->prt - set USART0 to 38400bps 5. Change the baudrate of U-Center to 38400bps 6. ubx->cfg->sbas : Disable 7. ubx->nav (not cfg->nav): double click on posutm, status, svinfo, velned. They should change from grey to black 8. ubx->cfg->cfg : save current config, click send
To save the configuration to a file: under the tools menu, choose GPS config, then click GPS>>file
Antennas
Sangshin
Part of interest: KSA-ST1580MS13
The Tiny 0.99 (not 0.9) and 1.1 were designed for this antenna however this part has not been verified for best performance yet.
Conclusion: [waiting for Jeremy to tell me how it worked]
Size: 13 x 13 mm
Center Frequency: 1580 MHz
Bandwidth: 5 MHz
@Fo: -15 dB
GAIN (dBi): 0 dBi
Ground Plane: 50 x 50 mm
Available From
Systronic INC. - Alberta, Canada
20mm Salvaged "No Name" Atenna
works best on Tiny 0.9 through 1.1
TransplantGPS
these guys are in MN and have 1580 18mm antennas in stock for $3.55/ea but they may want you to buy $50 worth or so: http://www.transplantgps.com/modules.html
Sarantel GeoHelix-P2
GeoHelix-P2 Passive GPS Antenna
This antenna apparently works great with the u-blox series GPS receivers so is not tied to any version of the board. It does not mount directly to the board. Impedence is 50ohm so almost any radio coax will work. Remember the antenna is passive with no RF amplification done at the antenna so every inch of extra coax introduces loss.