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Precision clock weird timezone LED issue
parrotycheck Posted: 2 May 2022, 07:39 PM
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Posts: 2
Joined: 2-May 22
I just put my clock kit together and had a blast doing it; it's been ages since I did any soldering but I've got a hankering to do more now! The big takeaways for me were:

* I really need a decent temperature controlled fine-point soldering iron
* Electronics have gotten really small now, the resistors and LEDs seem to be tiny compared to what I remember
* It's a lot of fun!
* Soldering plated through-holes is a trip.

Apart from one duff connection causing a missing digit, it worked perfectly the first time I powered it up... well, almost.

I have an odd issue with the GMT timezone LEDs.

At the moment I'm in daylight time so the bottom two timezone LEDs are on - and looking at the top two leds (I haven't put the panel on yet) I can see that the left hand one is veeeery faintly glowing, the right one is off entirely. If I disable DST - then the left hand LED comes on full brightness, but the right hand one doesn't come on at all.

The LEDs are both in the right way round, and they both work when powered from my multimeter's diode checker.

I've redone the solder joints, and they seem sound. The schematics (amazing that they're freely avaialble) show that the LEDs are connected in parellel so I have to admit that I'm completely floored here.

Any suggestions would be very gratefully appreciated!







Two additonal thoughts -

1) I'm in awe of how good the dyamic brightness control is; I haven't adjusted the VR at all and it's absolutely perfect, and goes down very nicely in dark conditions (though I did need to suppress the LED on the GPS board)

2) I think a really useful firmware revision would be if when it first starts up, it scrolls an 8 across all digits so that you can be sure all your segment joints are good. One of mine was faulty but it was very obvious - but if you have a faulty segment in the date section, you might not realise it for a long while!

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mit Posted: 3 May 2022, 11:13 AM
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yeah whatever

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Posts: 541
Joined: 4-May 16
Hi. That is pretty confusing behaviour for the LEDs. I admit it's unusual to wire them in parallel (especially without limiting resistors) but in practice this has been totally fine so long as their forward voltages are the same. I make sure never to mix batches, so they should be pretty well matched.

I would first try to clean the solder joints if you can, especially if you used extra flux. Sometimes the flux residue is partially conductive, and can occasionally cause strange errors. Although if you resoldered it and the behaviour didn't change, it probably isn't that. I think it may be best to assume that one or both LEDs are damaged or mis-manufactured, and replace the pair. I can send you some fresh ones if you send me an email.

On your other points:

1) I'm glad you like it! I have always been pleased with how the analog current-mirror circuit works.

2) Someone else suggested this beforehand and I forgot about it. I had a plan to add a "digit test mode", maybe by shorting a pin when you power it on. Perhaps a quick animation would be better.

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