GPS Atomic Time Sync

Discussion in 'Mac Apps and Mac App Store' started by alexkrishnan, Oct 15, 2009.

  1. alexkrishnan macrumors newbie

    Oct 15, 2009
    Hello, long-time reader, first-time poster around here!

    Hey Geeks!

    I am out on a nerdy mission tonight! I have recently moved to Santa Cruz, California, USA and I have discovered that the Atomic Clock that I have that syncs via the radio waves from WWVB in Boulder, Colorado does not obtain a strong enough signal to synchronize with atomic time.

    I know that GPS can provide an EXTREMELY accurate time stamp (within nanoseconds) if it has a valid time sample of about 24 hours. I have a nice Bluetooth GPS receiver, so I was wondering if anybody knew of some good mac software I could use to read the time stamp from my GPS receiver so that I can obtain accurate time.


  2. old-wiz macrumors G3

    Mar 26, 2008
    West Suburban Boston Ma
  3. alexkrishnan thread starter macrumors newbie

    Oct 15, 2009

    I have figured it out, and the solution is very geeky! For those fellow nerds who are interested and have a bluetooth and/or USB/Serial GPS reciever:

    1. Pair your bluetooth receiver using the normal setup assistant
    2. Download the cool software from furrysoft called goSerial at This software can send and receive serial data from any serial port in your mac (including bluetooth serial ports).
    3. Launch the app and you should see a configuration dialog. Under the "Port" tab choose the name of your newly-paired BT GPS reciever.
    4. Now we must set up the COM port settings as per the NMEA communication standard as detailed at This means that we must set the speed (baud rate) to 4800, Data Bits to 8, Parity to none, and Stop Bits to 1.
    5. Now click OK and press the button in the top right corner that looks like a plug. You should now see a bunch of text scrolling across the screen (if your GPS receiver has a valid fix).
    6. Now pause the readout by pressing the same button so that you can read through the output and interpret it.
    7. Read the section at entitled "Decode of selected position sentences".
    8. Read through your output and see which types of data your device is outputting. You will see many different line prefixes, but my bet would be that almost all devices will output a line that starts with $GPRMC, then a number (such as 123519).
    9. This first number after the comma is UTC time that is accurate within about a nanosecond, depending on your GPS unit. Of course there is about a 1 second delay before the data is actually transmitted and printed to the computer screen so you will still only see accuracy of about 1 second if you are viewing the live data output of your device.

    Post any questions/problems you run into if anyone is interested!


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