Jan Hoevers wrote: >> i wish to modify the wiring instructions given here: >> http://time.qnan.org/ > Saw that page a few weeks ago. Frowned on the idea of attatching > unbuffered leds to a time critical signal. Semiconductors do have a > capacity and I've never heard of high frequency leds. Apart from that a > pcb is overkill for two leds and a fuse. >> i will eliminate the circuit board and leds > Good, that's settled then. >> instead opting for an inline fuse > I would dump the fuse to. Even a fast blow fuse is much to slow to > protect the electronics of the usb port you use as power supply, so it's > useless. > Fuses are to prevent fire in the home. In a power supply the fuse goes > between the mains connector and the transformer, not on the output. > Besides, I've never seen a fuse in an usb device, I suppose usb ports > have an electronic overcurrent protection.
I wired up my GPS 18 LVC directly to a female DB9 connecter, with a hood to protect the soldered connections. I opted not to use a fuse or LEDs, as similarly, I've never seen a fuse in USB device (although the Garmin specs do call for a one amp fuse between the power source and the GPS), and the LEDs I just wasn't interested in. > Did you realize that once you use the pps, the rs232 is not time > critical anymore. The pps defines the UTC second boundaries, ntpd needs > the nmea data only to "label" the seconds. You could even forget about > the rs232 and use a ntp server on the internet for that "labeling". I also went this route. I use the shmpps driver from http://time.qnan.org/#driver-shm , which only provides the PPS signal. I get the time from internet servers. Even if I were to get the time from the GPS, I'd still want to have some internet servers in there for sanity checks anyway. As a side note, this also has the bonus of allowing me to avoid patching and recompiling the Linux kernel (which I have bad luck with ;)) to use LinuxPPS. I tried using gpsd, but I couldn't get it to read the PPS signal, it would only read the GPS time, which was fairly inaccurate. Does anyone run gpsd with the Garmin GPS 18 LVC and have it successfully read both PPS and GPS time? I'm interested to know, as I would rather go that route. The disadvantage to using the PPS signal only, is that the outside servers I use for time are clamped to minpoll (64sec) by the PPS driver, making my NTP server somewhat unfriendly to them. They would be polled at the same rate as the PPS signal (16sec) if I set minpoll 4, but I can't bring myself to poll an NTP server at such a rate. David Mills explained to me that polling the time source(es) at intervals longer than the time constant ntroduces a potential clockhop issue should the PPS signal fail, although I haven't had any trouble yet. So obviously I would like to use a local time source, which would eliminate those issues. Chuck wrote: > i wish to modify the wiring instructions given here: > > http://time.qnan.org/ You might also check out David Taylor's page on the same subject, http://www.david-taylor.myby.co.uk/ntp/FreeBSD-GPS-PPS.htm Regards, Dennis -- Dennis Hilberg, Jr. [EMAIL PROTECTED] NTP Server Information: http://saturn.dennishilberg.com/ntp.php _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
