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Those GPS 1pps problems. (Some bystander thoughts)
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"andyfoad@..."
Yesterday I thought I'd try to do a bit of research regarding the
GPS modules used by kit owners. Now I'm not sure if I've got all the model numbers correct but from what I've seen so far, all the modules have a very narrow 1pps width output. For example I've seen figures of nanoseconds and microseconds quoted on the troublesome modules, yet my Reyax UP501 which works flawlessly has a whole 100ms width for the 1pps output. From where I am standing it does seem that this pulse width is the key to it all. I remember some month ago some work by KA7OEI regarding using and RC network across the 1pps outputs might help broaden the pulses to work. Maybe a trawl through this groups archive might reveal some more ? Just thinking aloud... 73 de Andy G0FTD (Reyax UP501 GPS user with zero hassles) |
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g3zjo
On 16/06/2013 10:04, andyfoad@... wrote:
For example I've seen figures of nanoseconds and microseconds quoted onAndy Did the Rayax work on v2.01 The 1pps pulse width does seem to be tied up with the claimed accuracy for for timing / frequency purposes. Hans obviously knows how to handle long and short versions, a mid way compromise seems to be needed, if v2.01 had not got it right for the Trimble I may have been thinking about adding a Schmitt Trigger. Hans was still exuding confidence on a solution last time we spoke on the subject. I didn't comment at the time because I haven't tried it, but your tip of using an LED to detect the PPS signal I am fairly sure would not work on the Trimble GPS, its too quick for the Scope so I don't think the eye would catch it. 73 Eddie |
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Hans Summers
Hi Eddie, Andy Thanks for the thoughts on this. This is the next challenge - to make the GPS Interface work with both very short, and very long pulses.
I don't know if I mentioned it before, But I have what I call a "GPS simulator" which I use for testing such things. It basically is an ATmega168 (the same chip) programmed to produce a $GPRMC sentence and code the time and location into it, and a 1pps signal. It also has a button to toggle the GPS on/off which can simulate the effect of disconnecting it or it losing satellite lock. I am able to adjust the pulse-width in this "simulator". So with sufficient effort, I ought to be able to model the Trimble and the Rayax 501 and produce code which works with both of them, even though I physically own neither.
I believe the Rayax 501 worked with both U1 and U2 v2.01 and v2.02. So it is as Andy says - GPS modules with the very short pulse times seem to be the challenge.? 73 Hans G0UPL On Sun, Jun 16, 2013 at 10:33 AM, g3zjo <g3zjo@...> wrote:
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"David Atkins"
I tried a pulse-stretcher using a 555 [found on the net, not my design] with
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both a Trimble unit and a Sure development board. Neither of them had any success ;-( OTOH, the 555 isn't the best chip to use for this job. I just happened to have some in the junk-box. Anyway, I've ordered new processors for my Ultimates, so I hope my problems will be behind me soon. By the way, I want to use my Ultimates as portable units. Having a separate antenna makes it possible to put the transmitter in a strong metal box, but nearly all the 'recommended' GPS units appear to have integrated antennas which need delicate surgery to the case and make waterproofing more difficult. Any thoughts on that? David G8XBZ -----Original Message-----
From: QRPLabs@... [mailto:QRPLabs@...] On Behalf Of andyfoad@... Sent: 16 June 2013 10:05 To: QRPLabs@... Subject: [QRPLabs] Those GPS 1pps problems. (Some bystander thoughts) Yesterday I thought I'd try to do a bit of research regarding the GPS modules used by kit owners. Now I'm not sure if I've got all the model numbers correct but from what I've seen so far, all the modules have a very narrow 1pps width output. For example I've seen figures of nanoseconds and microseconds quoted on the troublesome modules, yet my Reyax UP501 which works flawlessly has a whole 100ms width for the 1pps output. From where I am standing it does seem that this pulse width is the key to it all. I remember some month ago some work by KA7OEI regarding using and RC network across the 1pps outputs might help broaden the pulses to work. Maybe a trawl through this groups archive might reveal some more ? Just thinking aloud... 73 de Andy G0FTD (Reyax UP501 GPS user with zero hassles) |
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dean smith
I second FTD,s remarks on the reyax UP501 modules... Faultless.. Plug n play ;-)
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g3zjo
On 16/06/2013 10:59, David Atkins wrote:
nearly all the 'recommended' GPS units appear to have integrated antennasHi David That is why I liked the Trimble, integrated antenna, and also an auto switched SMA antenna socket for use with an external (waterproof antenna). Otherwise you could use a separate waterproof enclosure for the GPS and waterproof plugs and socket to connect. 73 Eddie G3ZJO |
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"g8voip"
Hi Guys,
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Just in case anyone gets confused, there is no such thing as a Reyax UP501 GPS module! Reyax are simply one of several Far Eastern sellers on ebay. The GPS module being talked about was manufactured by Fastrax, since taken over by ublox (microblox). The UP501 is now an obsolete device now. Looking at the spec should have worked ok with the U2 as I believe the 1 PPS was edge detected in the first release of software and there was the facility to choose positive rising or negative falling edges (or simply invert). Operation with the U1 is far less certain as I recall there was a problem reported and Hans perhaps can confirm that the software uses 100mS as a cross over in the pulse window detector. The UP501 1 PPS signal according to the spec sheet is 100mS +/- a nats whisker so in theory might not work reliably. 73, Bob G8VOI --- In QRPLabs@..., dean smith <g7eob1@...> wrote:
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