[time] garmin gps25-hvs questions
Sat Dec 4 20:13:35 UTC 2004
On Sat, 04 Dec 2004 08:23:36 -0800, gnu not unix <gnu at wraith.sf.ca.us>
>In message <nvl3r0tqr0qcu41lnedimvo13qudm6easn at 4ax.com> you write:
>>worrying about calibrating for cable delays, etc. It is a Garmin
>>GPS25-HVS model (6-40 volt, rs232 output).
>I have a gps35-lvs and it has worked admirably here, as a
>reference clock working with ntpd.
>>2) Do I have to do anything special to the PPS output line in terms of
>>buffering, or do I just connect to the DCD pin? or some other pin?
>Yes, the PPS TTL level signal is not compatible with rs232.
>A MAX232 TTL to rs232 converter runs on +5 volts and will
>make the PPS compatible with the DCD pin on a pc's serial port.
>You will need a 7805 style +5 volt regulator to power this.
Note this is the HVS model, according to my reading of the pdf at
it swings from 0v to Vin, I was hoping this was good enough for the
serial port. In the short term it does no matter anyway as the initial
plan was just to connect it to a terminal emulator and grab some GPGSV
sentences and see how many (if any) satellites I can see, and how
strong they are. Would just sticking in a diode/transistor/resistor
http://www.buzzard.org.uk/jonathan/radioclock.html be enough?
>>3) If I connect all the unused pins on the serial port together via
>>diodes, is there enough power available to run the GPS rx (1W, 80mA)?
>>Or do I need to temporarily run it off a 12v sealed lead/acid battery
>>I have lying around?
>I'd not try sucking more than a few milliamps out of rs232 pins.
>Wire up a small fuse and connect to your pc's +12 rail. A ferrite
>core might help reduce possible spurious radiation.
this machine does not get switched off :-)
next planned reboot is when Debian 'Sarge' is released.
An out of date picture is at
since this was taken the windows laptop is now u/s, the ntp/webserver
that has been added is a 2nd box identical to the firewall that also
sits under the printer. Just plugging in a couple of serial cables
involved 30 minutes of fiddling and cursing.
>There are more details about PC's and ntp at this web site:
thanks - bookmarked
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