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Clock outputting complete garbage every second, only when updating while in sun.
Tkonk Posted: 29 Aug 2022, 05:09 PM
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I recently purchased 2 clocks as gifts; one works perfectly and is very cool, but the other displays complete garbage data on the display after acquiring a lock. It seems like it only does this when the clock is updating its time live and while it is in the sun during the day; at night it works completely normally. From research on other posts here, I believe that it is something along the lines of the temperature causing the clock speed of the attiny to change, causing problems when receiving the data from the GPS module (but I could be completely wrong). Due to the materials of my house, I cannot place it anywhere other than a window for it to acquire a signal so my theory cannot be ideally tested. I would obviously like to fix this problem before gifting them so any advice someone could share would be extremely valuable; I do not have a programming cable and, while I could, I would not like to purchase one if not necessary since I would have no other use for it than this one project.

Thank you for your time.

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mit Posted: 29 Aug 2022, 05:16 PM
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yeah whatever

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The first thing I would check is whether this happens if you use a different power supply. The fact it happens when the display is brightest suggests that there is electrical noise due to the high segment currents switching. A beefier power supply might solve the problem. If that does fix it, you might be able to improve the clock by adding some big electrolytic capacitors (say 10uF or 100uF) to the power input or even one on each display driver chip.

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Tkonk Posted: 30 Aug 2022, 06:02 PM
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This seems to have extremely mitigated the issue, enough for me to call it fine. While it still occasionally scrambles the output, as long as the brightness knob isn't set to max it usually is never noticeable unless you sit there and stare at it for 15 minutes. I was just worried I had messed up building one of my clocks since of the 2 random phone charger bricks I tried, one of the clocks was fine with either of them and the other one was having the problems previously stated. Turns out they were both 5v 1a so I found one that was 2a and here we are.

Thank you for your time, my issue is solved; no further reply is required.

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mit Posted: 31 Aug 2022, 08:14 AM
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yeah whatever

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It is interesting that one clock is affected more than the other. You could try swapping the ATtiny chips between the clocks to see if one is more sensitive to noise (or perhaps one set of driver chips is more noisy).

Do consider adding some capacitors, you can make use of the space next to the optional regulator near the middle of the board. If you fit a big electrolytic capacitor into the unpopulated 1u footprint it should help. Make sure to check the polarity, the ground pin should be identifiable by its connection to the ground plane.

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