[time-nuts] Best Chance GPS module

Nick Sayer nsayer at kfu.com
Sun Mar 19 10:57:43 EDT 2017


Ok. It wasn’t totally clear from your earlier message what you were looking at, but just be aware that the LED pin is just a “blinkenlichten” pin that means almost nothing. You have to actually separately look at the PPS pin to see what it’s doing. There’s (almost) no connection between the activity on the two pins.


> On Mar 19, 2017, at 2:13 AM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
> 
>> On Dec 1, 2016, at 7:44 AM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
>> 
>> 
>> Venus838LPX-T.   Seems to go into a non-locked state for a proportion of the time but still emits a PPS signal, which increasingly deviates from true UTC.  That's using a 25 mm square 28 dB active patch antenna, similar to the antennas on other similarly located GPS receivers.  This was indoors, on the top floor of a two-storey building, with just the power fed to it, watching the LED flash.
>> 
>> Maybe I was unlucky?  I wonder what experience others have?
> 
> From: Nick Sayer via time-nuts
> 
> Was the LED on the PPS pin or on the FIX pin?
> 
> The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what the rules are for it. When things are working properly, it blinks at 0.5 Hz, but the leading and trailing edges are something like 120-150 msec after the second. It’s very, very loose. My own interpretation is that the controller flips the bit when it’s got nothing better to do.
> 
> I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, but it’s not a failure mode I’ve expended a lot of effort to examine.
> ===================================================
> 
> Nick,
> 
> I had to dig out the module to check, but as far as I can tell the LED is connected to pin 7 on the chip, listed as GPIO0/LED on the data sheet. Nominally, navigation status.
> 
> The PPS output which I was monitoring comes from the PPS pin (40) on the chip - GPIO3/P1PPS1
> 
> Cheers,
> David
> -- 
> SatSignal Software - Quality software written to your requirements
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> Email: david-taylor at blueyonder.co.uk
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