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  • Adding GPS to my RPi2

    Got a small USB with cable GPS receiver (Earthmate LT-20) and thinking if it could be integrated to my FR24 feeder ADSB receiver. I was able to run it using other Linux distros and hoping it will work on RPi2. I want it to run together with FR24 feeder. If this question already exist please point me to the link. Thanks

  • #2
    What do you hope to achieve with adding one.

    The FR24 supplied boxes use GPS for time and location accuracy.

    With USB TV sticks and the software we install your location is specified at the time of setup and time is sycnronised with NTP via the software calling it like others around you with the same devices. A GPS will likely only add time adjustments that NTP will then fight.
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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    • #3
      I see thanks for the input. I was thinking it could help the feeder to be more accurate aside from what i provIded during the setup. Anyway, i wont bother to add it on my box. I will maybe do other expirement with it. I appreciate your answer.

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      • #4
        The only GPS units that FR24 is using is the one connected to the FR24 box. Using a USB port to connect a GPS destroys most timing, because of USB latency.

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        • #5
          Got it Mike. Thanks for the helpful info.

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          • #6
            Mike,
            Would a GPS receiver that uses the GPIO on the RPi work any better than a USB GPS device?
            Thanks

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            • #7
              Originally posted by StupidDoes View Post
              Mike,
              Would a GPS receiver that uses the GPIO on the RPi work any better than a USB GPS device?
              Thanks
              Yes, there is a pulse per second feature built in the ntp, driver 22. If you use this with a GPS derived PPS signal, connected to one GPIO of the Raspberry, its system clock will sync much more precisely than with clicks from other NTP servers around. NTP will manage this well without letting the PPS signal fight against the other time sources. Accuracy will become as good as some few microseconds rather than a couple of milliseconds without PPS.
              To make things better: using a serial GPS receiver, you might provide position and time with much less jitter than via USB. The PPS thing is not dependant on any GPS position feed though. PPS is NTP-related.
              Do not expect the setup as a plug and play one. There are bad GPS receivers out there. You have to tweak things.
              By the way: As far as I know, the flightradar application does not improve with precision of the system clock. Even the MLAT thing cannot participate from a better system time (yet?).

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              • #8
                Do not expect the setup as a plug and play one. There are bad GPS receivers out there. You have to tweak things.
                So what GPS module would you recommend?? I was looking at one of the microstack ones off ebay?

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                • #9
                  Sorry, newbies on this forum are not allowed to post links.

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                  • #10
                    The simple point is, Investing in a GPS unit won't help anyone currently and will be a waste.

                    The software is hardcoded to probe NTP periodically and sync before sending data as part of its processing. Adding a device won't change that.

                    (unless of course you have it for other reasons outside the FR24feed process)
                    Last edited by Oblivian; 2016-01-05, 22:17.
                    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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                    • #11
                      GPS Receiver / defeating funny forum software

                      Originally posted by StupidDoes View Post
                      So what GPS module would you recommend?? ....
                      Recommending is somehow difficult, because I did it once. Which level of experience do you expect from such a person? To understand this statement read: "could be link" (this phrase denotes a link, which I am not allowed to post here)
                      OK, I use this one: "could be link" and from what I am reading, Ublox Neo6 or higher devices do a pretty good job. For getting the PPS signal, you have to solder a wire to Pin3 of the Ublox module. "could be link" After some search you should be able to identify a device with the PPS signal connected to a soldering point as such.
                      If you want to dig deeper, try: From this website you can get ample information on what to do. "could be link" But my last clue again is: For using PPS and gaining great time accuracy you do not need a GPS time input necessarily but PPS from GPS. You might use the common NTP scheme as well. Precision is about intergrating the PPS functionality, most easy from a GPS receiver. PPS is setting up NTP and (preferably) GPIO 18 on the Pi. Just one pin, no recompile of NTP, which you probably will find in old howtos.
                      Enable PPS via device tree and edit ntp.conf. Eventuelly install GPSD for gaining full GPS functionality.

                      This forum software is funny, stating: "Sorry rueckwaertsflieger, you are not allowed to post links in the forums. You must have a minimum of 4 posts in order to post links. You currently have 4 posts."

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                      • #12
                        Originally posted by rueckwaertsflieger View Post
                        This forum software is funny, stating: "Sorry rueckwaertsflieger, you are not allowed to post links in the forums. You must have a minimum of 4 posts in order to post links. You currently have 4 posts."
                        Im having the exact same issues yet as of posting this I have 7? there a few on ebay but im not sure if these are just your typical cheap Chinese SH! or not. albeit there of a 12-17 id be more than prepared to spend that little bit extra on one that actually works correctly and not going to break after a few uses!
                        Cheap one
                        Higher priced one

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                        • #13
                          (For the last time,) please be aware, the GPS rceiver will give no advantage for an ADS-B app. It is quite some kind of an effort to implement the PPS improvement for system clock precision.
                          The cheap one is the one I am using successfully. Big disadvantage is you have to have advanced soldering skills to pick up PPS. The higher priced one exposes the PPS signal to a "real" pin on the header besides the all expected RxTx signals. Should work also. In case, I am allowed to post links here, I will report them later.

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                          • #14
                            yes but you could learn from the experiance and you would end up with your NTP time server for everything else in your home

                            http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html

                            i learned a lot from this page in setting up a ntp server on a beaglebone.
                            T-EGLF8

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                            • #15
                              Yes SpaxmoidJAm, thank you, that's one of the good references I cannot post here.

                              @StupidDoes
                              Please pay extra attention to section "Configuring Linux for PPS on the GPIO port" because recent Raspbians definitely do require less things to do than older tutorials say, guess how I know - summary at the end. If you want use the GPS time feed additionally you best install gpsd, though ntp is even enabled to read from serial port GPS without GPSD module as well, using driver 20 (without gpsd). Have fun.


                              Things to do with a raspberry, when attaching a serial GPS receiver - short form:

                              Serial port, if you want connect the GPS feed, use the whole story (I guess you want)
                              free the tty at boot time, in:
                              /boot/cmdline.txt commentout:
                              # `console=ttyAMA0,115200`
                              # and `kgdboc=ttyAMA0,115200`

                              remove/comment the default tty configuration.
                              /etc/inittab comment out
                              # Spawn a getty on Raspberry Pi serial line
                              # T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

                              Todo for PPS kernel support
                              /boot/config.txt add
                              dtoverlay=pps-gpio # default-pin is 18
                              init_uart_baud=9600 # only if GPS is attached to UART (serial port)

                              pps-gpio module to be loaded at boot time, in:
                              /etc/modules add
                              pps-gpio

                              Then proceed with editing ntp.conf regarding the link from SpaxmoidJAm.

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