Getting a Garmin working and hacking it up?

[rwgast_lowlevellogicdesin]

Wasn't sure where to post this..... I have been working on a huge remotely controlled Software Defined Radio station, and the SDRs will all be connected to a RAS PI on top of a mountain behind my house, they will then use RTL TCP to send all the data down the hill to my main PC for DSP and recording, the main PC will use GNU Radio to modulate any data that needs to be transmitted then send the nicely modulated file backup the hill via wifi to the pi who will TX it using a custom built transmitter.

Well you can imagine if a Pi3 along with 6 RTL sticks that have more mods done to each one costing more than the stick get stolen.... not to mention the DC-Microwave antenna switching systems for bot wifi and RF. What s the answer...... well GPS of course! The pi needs to report its cordinates every few minites #1 and if it s stolen the will hopefully still be L band access so if the thief plugs it end the GPS will ping iridium and message me! Also GPS is usefull for othe RF applications.

I got a few cheapo 7 dollar sticks on ebay they used a ublox 7 chip and did GPS a long with glonass. The system worked great it just used a USB to serial chip and sent the nema info over a com port. Well for some reason after a few days of sitting in a drawer when I plugged them in they didnt work.... the 1pps light was sold and the computer didnt recognize any USB device. Im quite annoyed, there cheap but they take weeks to arrive!

I got a working Garmin Nuvi 200 for free, well it works but it doesnt have the flash card with the software I am assuming I should be able to get that for free from garmin and put it on my own flash card? I know the screen just shows the logo without there maps stuff, im not sure if it needs it to get a gps lock or not. What I would like is to take the thing apart and hopefully be able to push the gps and sat info to a USB to serial dongle and also tap on to the 1pps to use as a lock for some timing stuff. The super cheap Ublox had all these capabilities so anyone know if a garmin pcb can do the same stuff? I really have no need for the thing otherwise I mean google maps works fine on my phone...

[gnif]

I used the ublox in a project recently, the issue with them is they have a super cap to store their configuration data. Sitting in the drawer it likely went flat and lost its baud rate settings. If you look up the datasheet there are some configuration pins you can use to hard wire it's configuration. I made mine drop into the UBX binary protocol by pulling the config lines low, which is their own protocol, but fully documented and much faster to handle due to the lack of conversions from text to int/float, etc.

Code: [Select]

  while(true)
  {
    /* look for UBX sync bytes */
    if (chSequentialStreamGet(&SD2) != 0xB5 || chSequentialStreamGet(&SD2) != 0x62)
      continue;
 
    /* read the common header values */
    ckA = ckB = 0;
    ckA += (ubx.msgClass = chSequentialStreamGet(&SD2)); ckB += ckA;
    ckA += (ubx.msgID    = chSequentialStreamGet(&SD2)); ckB += ckA;
    ckA += (ubx.length   = chSequentialStreamGet(&SD2)); ckB += ckA;
    ckA += (tmp          = chSequentialStreamGet(&SD2)); ckB += ckA;
    ubx.length |= tmp << 8;
 
    /* read the payload */
    for(i = 0; i < ubx.length && i < sizeof(buffer); ++i)
      { ckA += (ubx.data[i] = chSequentialStreamGet(&SD2)); ckB += ckA; }
 
    /* verify the checksum */
    if (chSequentialStreamGet(&SD2) != ckA || chSequentialStreamGet(&SD2) != ckB)
      continue;
 
    gps_process_packet(&ubx);
  }


[Ian.M]

I doubt its worth hacking the Nuvi.  Its highly integrated with no NMEA0183 output capability.  Sell it on and put the money towards a suitable module with NMEA0183 and 1pps output.

[LabSpokane]

If all you want is NMEA 0183 output and 1pps, try this:

https://buy.garmin.com/en-US/US/oem/sensors-and-boards/gps-18x-oem/prod27594.html

Fairly cheap, robust and dirt simple.