PPS missing

Stations Receivers
1

Hello,

The antennas on the sensor gnome that I am working with are reading at normal detection rates, however, the GPS and clock are reset to 2000-01-01. The PPS is not present and reads ‘PPS missing’. The sensor gnome software is up to date. We tried to reboot, but this did not solve the problem. Is this a problem with the GPS SM?

In addition, the sensor gnome is not recording as it usually does. Typically, when I download the data off the microSD inserted to the RaspberryPi, a folder is created automatically per day, yet the sensor gnome is not currently doing this. The folders all are dated to the year 2000. Are these issues related?

I am new to this technology and could not find answers on the Motus site, this google group, or sensorgnome.org. Any insight to this issue would be much appreciated.

Thank you!

2

SG sets date/time from GPS regardless of PPS being present or not. 2000-01-01 is the default date in the absence of GPS which would suggest a possible issue with your GPS module?

3

But… if it is internet connected, it takes the time from internet.

4

My SG are offline on test prior to deployment in the field so have no experience of internet being used as a time source. The only time source available to them is their GPS. Use of the default date of 2000-01-01 suggests the SG cannot find any valid time source at all?

5

Hi Michael,

The symptoms you describe are consistent with the GPS not getting a satellite fix so not updating the system time.

There’s no real time clock in a SG so when it first boots up the system clock defaults to 1970-01-01 00:00 and starts counting from there. When the GPS gets a satellite fix it updates the system clock to whatever the GPS satellites are sending it.

The PPS signal is generated by theGPS but if there’s no fix then there’s no PPS.

Here’s a few things to check:

  • Is the “FIX” LED on the GPS board blinking? see
    https://docs.motus.org/sensorgnome/appendix/anatomy
    & the GPS sections of
    https://www.instructables.com/Raspberry-Pi-SensorGnome/#solder

  • If this isn’t blinking at all then there is likely to be a problem with the connection between the GPS as the main Pi board, or the GPS has an internal problem.
    Try reseating the GPS board.

  • The FIX LED has two states:

  • Blinking on and off once every other second - NO FIX

  • Blinking once per 10 seconds or so - HAS FIX

  • If the FIX LED indicates it has a satellite FIX then there’s likely to be an internal software problem, but that’s beyond my understanding to help diagnose.

  • If you have no FIX, can you move the SG to get a better view of the sky.

  • Are you using an external antenna?
    If so check the fit of the ufL connector where it attaches to the GPS board.
    This connector is very fragile so avoid twisting or using force to fit it.

6

My SG running on an RPi 3B+ gave me the ‘PPS missing’. After trying many things, I ordered a RPi 3B and the problem went away.

7

@Ewan thank you. My SG, 2 x 3B, are running as they should with GPS solid complete with PPS.

@genedodd highlights something I certainly missed in the original @agpel post that their hardware was a 3B+. As I understand it the current stable release only runs on a 3B?