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

Mark Hansen meh at NOSPAMwinfirst.com
Wed Jan 18 15:21:25 UTC 2006

On 01/17/2006 05:49 PM, Richard B. Gilbert wrote:
> 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.

Thanks. I found that Garmin sells a PC version of this receiver, which
is made to plug into the serial port, so no adapters/converters are
necessary. Here's a link to someone that sells it:


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