Diagnosing GPS Issues

All variants of Notecard Cellular and Notecard Cell+WiFi include a GPS/GNSS module for gathering location data in outdoor settings. This guide is meant to help diagnose and resolve some of the most common issues users encounter when building location-aware applications.

• Avoid Simultaneous Usage of Cellular and GPS
• Verify Antenna Connection and Device Placement
• Other Issues and Potential Solutions

Avoid Simultaneous Usage of Cellular and GPS

The Notecard is not designed to allow for simultaneous usage of both the cellular radio and GPS/GNSS module, due to limitations of the cellular modem itself. Location-aware applications must be built with this in mind.

note

If concurrent use of cellular and GPS is required in your solution, we recommend using an external GPS module.

Using Continuous Mode for Both Cellular and GPS

The Notecard does not support running both a continuous cellular connection ({"req":"hub.set", "mode":"continuous"}) and continuous GPS ({"req":"card.location.mode", "mode":"continuous"}). If you attempt to set both to continuous mode, the Notecard will return an error:

{"err": "cannot simultaneously use continuous card.location.mode and hub.set modes"}

Solution: Use periodic mode for one or both of hub.set and card.location.mode requests, being aware of other potential issues with short connection cycles (see below). Or use an external GPS module.

Using Periodic Mode with Short Connection Cycles

A common workaround to effectively enable continuous mode for both cellular and GPS/GNSS is to set one or both to periodic mode, but then either sync data (with cellular) or gather location data (with GPS/GNSS) on a too-frequent basis (e.g. < 5 minutes). This effectively puts the Notecard into continuous mode for either technology, but doesn't fail as gracefully as the error provided above. This is because the Notecard ends up constantly fighting with itself to enable either cellular or GPS/GNSS, with the net effect of neither of them working well (or at all).

To better explain this with an example, if GPS/GNSS is in periodic mode and the seconds value is very low (e.g. {"req":"card.location.mode", "mode":"periodic", "seconds":30}), location will be sampled every 30 seconds (if the Notecard detects motion during that period). This effectively doesn't allow the Notecard to enable the cellular radio at all during periods of consistent motion.

Solution: Make sure the outbound and inbound arguments in your hub.set request are set at a value >=5 minutes (e.g. {"req":"hub.set", "mode":"periodic", "outbound":60, "inbound":360}). Likewise, make sure the seconds argument of your card.location.mode request is set to the highest value possible to gather location data (e.g. {"req":"card.location.mode", "mode":"periodic", "seconds":6000}).

Not Providing the GPS/GNSS Module Enough Time

The Notecard will not enable the GPS/GNSS module until it has made a successful network connection upon startup to obtain the current time. In addition, when first enabling the GPS/GNSS module after a cold boot of the Notecard, expect the Notecard to take at least 1-2 minutes to acquire ephemeris data and identify locations of GPS satellites.

Likewise, when the Notecard switches between cellular and GPS/GNSS modes (or vice versa) be aware that it can take up to a minute (or longer) to reestablish a cellular connection or to re-orient with GPS satellites.

Solution: Monitor the current status of the GPS/GNSS module by inspecting the status field in a card.location response. The [x] sats value will identify how many satellites the Notecard can see.

{
  "status": "GPS updated (58 sec, 41dB SNR, 9 sats) {gps-active}
            {gps-signal} {gps-sats} {gps}",
  "mode":   "periodic",
  "lat":    42.577600,
  "lon":    -70.871340,
  "time":   1598554399,
  "max":    25
}

Verify Antenna Connection and Device Placement

Many GPS-related issues are easily resolved by double-checking the GPS antenna and the physical location/orientation of the device itself.

Check the Antenna Connection

Verify that the U.FL connector from the antenna to the Notecard is seated properly. When seated properly, you will feel it "click" into place. If the U.FL connector is not fully secured, this will prevent any signal from getting through.

If you're using a Notecarrier with onboard antennas, ensure the connector labeled GPS is properly seated on both ends of the connection (i.e. on the Notecard and the antenna).

Ensure No Antenna Signal Interference

Antennas that are touching/too close to metal objects or other devices that produce electro-magnetic interference (EMI) may prevent the establishment of a cellular connection. This is most often an issue when using a Notecarrier with onboard antennas, like the Notecarrier A.

If using the Notecarrier A (or any previously sold Notecarrier with onboard antennas), ensure that there are no metal objects within the regions labelled "Keep-Out Zones". These regions represent an 11 mm cylinder around the cellular and GPS antennas mounted on the board. You should also consider elevating the Notecarrier from the table surface and moving it away from your laptop computer and other metal objects.

Ensure the Antenna is Not Damaged

Flexible antennas that are cut, or board-mounted antennas that have broken free, have been sources of connectivity issues for some of our customers.

Verify the Type of Antenna

If using an external GPS/GNSS antenna with your Notecard, be sure it supports a broad frequency range of 1164 MHz to 1591 MHz (depending on which GNSS solution you are utilizing).

Make Sure Antenna Has Clear View of Sky

It is extremely difficult to access GPS/GNSS satellites when indoors. Therefore, be sure the device is located outdoors with a clear view of the sky (i.e. verify there are no physical obstructions like buildings or trees that may be blocking access to the satellites).

Other Issues and Potential Solutions

Wideband vs Narrowband Notecards for GPS/GNSS

Use of a wideband (WB*) Notecard has proven over time to provide a better experience when using GPS/GNSS for location tracking. An added benefit is the cellular radio used on the wideband Notecards generally allows for improved cellular signal strength and quality.

Gathering Detailed Trace Log Data

If requested by Blues Support, it is possible to capture a more detailed log of GPS activity beyond what appears in the responses to a card.location request.

Connect your Notecard/Notecarrier to the In-Browser Terminal and issue the trace +gps command. You will see a stream of data related to the GPS module. This data can be sent to Blues for further investigation.

Arduino GPS Example

Some best practices for using the Notecard's GPS module with Arduino are included in the Cold Chain Monitor accelerator application. Specifically, the referenced function in this sketch on GitHub.