Hardware

Waspmote can integrate a GPS receiver which allows to know the exact outside location of the mote anytime. In this way the exact position of the mote can be obtained and even the current time and date, to synchronize the Waspmote internal clock (RTC) with the real time.

• Model: JN3 (Telit)

• Sensitivity:

  • Acquisition: -147 dBm

  • Navigation: -160 dBm

  • Tracking: -163 dBm

• Hot start time: \<1 s

• Cold start time: \<35 s

• Positional accuracy error: \< 2.5 m

• Speed accuracy: \< 0.01 m/s

• EGNOS, WAAS, GAGAN and MSAS capability

Antenna (Waspmote OEM):

• Cable length: 9 cm

• Connector: UFL

• Gain: 24 dBi (active)

Antenna (Plug & Sense!):

• Cable length: 2 m

• Connector: SMA

• Gain: 26 dBi (active)

Available information: latitude, longitude, altitude, speed, direction, date&time and ephemeris management

Figure: GPS Module

Note2: The test points named as A, B, C and D are not used to obtain GPS position information and there is no need to use them in any of the features described in this guide. They are just for test purposes and other not relevant features. They correspond with module pin-out as follows:

• A - 1PPS

• B - SCA

• C - SCL

• D - V_BAT

Due to the GPS signal is weak inside buildings, It is recommended to use the GPS module outdoors, with a direct line of sight to the sky. This will ensure the necessary signal quality to obtain valid GPS data.

The GPS module gives us information about:

• latitude

• longitude

• altitude

• speed

• direction

• date/time

• ephemeris

The functions implemented in the API allow this information to be extracted simply, calling functions such as:

{
    GPS.getAltitude();
    GPS.getSpeed();
    GPS.getLongitude();
    GPS.getLatitude();
}

The GPS receiver uses the UART_1 to communicate with the microcontroller, sharing this UART with the other modules plugged on socket 1. As the 2 modules share this UART, a multiplexer has been enabled in order to select the module with which we wish to communicate at any time. This is not a problem; since all actions are sequential, in practice there is parallel availability of both devices.

The GPS starts up by default at 4800 bps. This speed can be increased using the library functions that have been designed for controlling and managing the module.

The GPS receiver has 2 operational modes: NMEA (National Marine Electronic Association) mode and binary mode. NMEA mode uses statements from this standard to obtain location, time and date. The binary mode is based on the sending of structured frames to establish communication between the microcontroller and the GPS receiver, i.e. to read/set ephemeris.

The different types of NMEA statements that the Waspmote's built in GPS receiver supports are:

• NMEA GGA: provides location data and an indicator of data accuracy

• NMEA GSA: provides the status of the satellites the GPS receiver has been connected to

• NMEA GSV: provides information about the satellites the GPS receiver has been connected to

• NMEA RMC: provides information about the date, time, location and speed

• NMEA VTG: provides information about the speed and course of the GPS receiver

• NEMA GLL: provides information about the location of the GPS receiver

The most important NMEA statements are the GGA statements which provide a validity indicator of the measurement carried out, the RMC statement which provides location, speed and date/time and the GSA statement which provides information about the status of the satellites the GPS receiver has been connected to.

(To obtain more information about the NMEA standard and the NMEA statements, visit the website:

http://www.gpsinformation.org/dale/nmea.htm

Figure: GPS module connected to Waspmote