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GPS Fix LED
TreKKiwL Posted: 22 Feb 2021, 02:02 AM
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Joined: 21-February 21
Hi Tim,

Great Kit!! (#225

I enjoyed putting it together but mine was one of the kits with faulty display drivers. That problem fixed.

Now I notice that the 'GPS FIX' Led is very, very dim and appears to be 'on' all the time. Closer inspection showed a very short time when it would go off, in time with the PPS signal.

Using an oscilloscope, showed an 8ms pulse going from HI (2.93V) to LO (o.3V), hence the reason for always appearing to be 'on' .

I have removed the two displays in that area so I could recheck my soldering, replaced resistor and LED (even though both checked OK).

Checked continuity of tracks, etc but still I have a very dim GPS FIX led which seems to be pulsing opposite to what I would have thought.

Everything about the clock works fine and I know the GPS FIX led is redundant, but I would just like to know. I have run out of ideas.

Don

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mit Posted: 22 Feb 2021, 01:02 PM
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yeah whatever

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Joined: 4-May 16
Hi, that is interesting. There are only two possible reasons:

- something is shorted (but by the sound of it, that's unlikely)

- the GPS module is behaving differently to expected

I can completely believe the second reason, the GPS modules have been sent with possibly different firmware on them at least twice in the past. I don't think it's possible to update their firmware, but you can find out what it's running by listening to the serial data it outputs during power-up.

So long as the rising edge of the pulse is aligned to the start of the second, the clock display should still be accurate. Have you compared it to some other time sources? Although I suppose it would be very hard to spot if it was out by only 8ms.

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TreKKiwL Posted: 22 Feb 2021, 08:02 PM
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Joined: 21-February 21
Hi Tim,

Yes, I had more or less came to the same conclusion that the GPS module may be the cause, however, I don't (at this stage) have a second unit to swap it with. I have two more on order, from different sources, but have yet to arrive. I will let you know of the result.

The only other time source I have it Time.Is on the computer, and can't see any difference. As you say, 8ms is hard to see!!



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