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).

• Positional Rate of 4Hz
• Supports Active or Passive Antennas
• Supports DGPS, WAAS, EGNOS, and MSAS

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

Sangshin Distributors

Systronic INC. - Alberta, Canada

20mm Salvaged "No Name" Atenna

works best on Tiny 0.9 through 1.1

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 Passive GPS Antenna

This antenna apparently works great with the u-blox series GPS receivers. 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.