[ntp:questions] Re: Looking for time sync hardware supported under Linux for under $400?

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jan 18 01:49:30 UTC 2006

Mark Hansen wrote:

> On 01/17/2006 12:01 PM, Steve Kostecke wrote:
>> On 2006-01-17, Mark Hansen <meh at NOSPAMwinfirst.com> wrote:
>>> It is possible to find a time synchronization device which is
>>> supported by the NTP software (NTP version 4.2.0.a on CentOS 4.2) for
>>> under $400?
>> Garmin GPS-18LVC
> Thanks. Can I please ask a couple other questions about this?
> The documentation for it says that the serial interface is TTL levels
> (which are 0-5v, if I understand correctly), rather than what would be
> expected by a PC serial port (which are 0-15v, again IIUC).
> Can this just be connected to the PC serial port, or will I have
> to build/buy a TTL -> RS-232 converter/adapter?
> I looked through the 'Comprehensive list of clock drivers' supplied with
> the NTP software, and didn't see this device mentioned. Is it know by
> another name to the NTP software?
> Thanks again!

You will need to shift the levels;  RS232 uses both positive and 
negative voltages for signaling.  I believe that there is a chip that 
will convert TTL to RS232 levels.  I vaguely recall a number like MC1447 
but that's just a vague recollection; get the facts before you spend 
your money!  You will, of course, need both positive and negative supply 
voltages; I think +/- 12VDC will get the job done and you might even get 
away with +/- 5VDC.

The Garmin  GPS-18LVC uses the NMEA driver.

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