On Thu, Nov 15, 2012 at 4:30 AM, David J Taylor <david-taylor@blueyonder.co.uk> wrote: > i just used this to with a raspberry pi with good success. > > https://www.adafruit.com/products/746 > > james > =============================================== > > It looks idea, James, but ... with the 15 mm square patch antenna it seems > deaf compared to similar devices with 25 mm antennas. Perhaps > understandable, but I just bought one and it's been sitting for well over an > hour and not yet acquired lock. The device I bought from China, sitting > next to it, has been happily locked for that whole period. (As I'm running > a test I don't want to unlock the other device). Just a caveat for someone > considering using these devices indoors - size matters! > > 25 mm antenna device: > http://www.satsignal.eu/ntp/NEO-6M-under-initial-test.jpg > http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html > > Cheers, > David > -- > SatSignal Software - Quality software written to your requirements > Web: http://www.satsignal.eu > Email: david-taylor@blueyonder.co.uk > all good points David. I originally had place mine close to a window to get a lock as it could not acquire any satellites in my home office otherwise. I don't have a south facing window and my office is on the first floor of a two story house. That may or may not have played a part but just placing it near the window and facing outside worked fine. I added the antenna (https://www.adafruit.com/products/960) and the connector (https://www.adafruit.com/products/851) and now I don't have to keep my RPi and gps near the window. What I liked about this one was it would interface with the RPi GPIO pins without having to use a converter from RS232 to 3.3v and I never considered a USB gps due to the inherent issues with USB and timing. Thanks, James

From: james machado [] all good points David. I originally had place mine close to a window to get a lock as it could not acquire any satellites in my home office otherwise. I don't have a south facing window and my office is on the first floor of a two story house. That may or may not have played a part but just placing it near the window and facing outside worked fine. I added the antenna (https://www.adafruit.com/products/960) and the connector (https://www.adafruit.com/products/851) and now I don't have to keep my RPi and gps near the window. What I liked about this one was it would interface with the RPi GPIO pins without having to use a converter from RS232 to 3.3v and I never considered a USB gps due to the inherent issues with USB and timing. Thanks, James ============================================= Well, after 5 hours the Adafruit unit finally locked - must have been just the right combination of satellites! I was slightly surprised by the difference in antenna size. It would have to be placed near a window for normal use. Like you I have some puck antennas which I've used on other GPS devices, with the GPS 18 LVC being placed on the roof (it's not very sensitive), the GPS 18x LVC and the other units being placed indoors, some on a south-facing wall, but all on the top storey of a two-storey house. Having the extra antenna cable allows more versatility in placing the unit, but these are so small - even /with/ the computer, that it's a choice between antenna cable or Ethernet/power cable. The 25 mm antenna NEO-6M board I got also has 3.3V interfacing which, as you say, is a bonus. USB would suit as a source of coarse seconds if you needed a stand-alone unit for operation when out portable, although, as you will know, the Raspberry Pi also has a serial interface you can program for two of the GPIO pins, freeing up the USB ports for something else. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-taylor@blueyonder.co.uk

On Thu, Nov 15, 2012 at 9:02 PM, Jim Lux <jimlux@earthlink.net> wrote: > > > ALl good ideas.. but I was looking more for something a bit more > packaged.. like a hockey puck with wires coming out. > > Me too, please. Something with a PPS, and an RS-232 output, withour soldering. -- Sanjeev Gupta +65 98551208 http://www.linkedin.com/in/ghane

On Thu, 15 Nov 2012 15:06:10 -0000, "David J Taylor" <david-taylor@blueyonder.co.uk> wrote: >-----Original Message----- >From: David >[] >So the 16x manual says. As far as I know, all of the Garmin LVC, HVC, >and 5Hz versions of their receivers have a timing pulse output. > >The GPS18 series that I have was replaced by the GPS18x series. > >Some of their receivers have "TIA-232-F (RS-232) Compatible Polarity" >which means exactly that. They do not provide RS-232 voltage levels >so for my GPS18-5Hz, I had to hack together a little non-inverting >level shifter (two transistors, some resistors, and a dual power >supply) to convert the 0 to 5 volts into -12 and +12 volts. >=================================================== > >I must have been lucky with my combination of 18, 18x and various PC serial >port receivers, as I haven't needed a level shifter with either. But the >slightly less than 3V from a different 3.3V GPS does /not/ register on a >different serial port. > >Circuits: > http://www.satsignal.eu/ntp/GPS-interface-1.png > http://www.satsignal.eu/ntp/GPS-interface-2.png > >from: > http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm None of those circuits would have worked for me. The GPS18-5Hz manual says "0 V to Vin, between 4 and 5.5 V (Asynchronous Serial, TIA-232-F (RS-232) Compatible Polarity)" and as far as I know, most if not all of the other Garmin serial outputs are similar. The timing and polarity are RS-232 compatible but the levels are not. RS-232 traditionally requires a minimum of -3 and +3 volts, in between is undefined, and -12 and +12 volts is more typical to provide sufficient noise immunity for error free operation at high speeds and with long cable runs. In addition, since the serial output is "Compatible Polarity", it is not inverted so it cannot be directly used with an RS-232 level translator because they all expect an inverted logic level signal. That is easy enough to fix with a single transistor inverter but still annoying. It is doubly annoying when you consider that interfacing it directly with a standard UART would also require an inversion. I gather than some serial ports, like those on many USB to serial dongles, will work with the nonstandard 0 to 5 volt levels but none of my equipment will. My temporary solution was to build a little two transistor level shifter so I can play with the GPS18-5Hz and decide if it is worth working with: http://www.banishedsouls.org/c2df3757f1/GPS18/RS-232.jpg On that board there is also a simple RS-232 to logic level driver so the computer can talk back to the GPS18-5Hz (I had to upload new firmware and configuration data.) and a shunt mode 50 ohm cable driver to unload the 5 pulse per second output. The shunt mode 50 ohm cable driver is rather power hungry but produces an exceptionally clean output. My current plan is to build an improved level translator so I can move the GPS18-5Hz to the peak of my roof and use a standard cat-5 cable for simple 12V power, bidirectional RS-232, and a clean 5 pulse per second signal. After I get an OnCore receiver that supports sawtooth correction, the GPS18-5Hz can feed a local NTP server instead of a GPSDO.