| kotor2knight | Posted: 5 Nov 2025, 01:22 AM |
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 Member Posts: 4 Joined: 5-November 25 |
My clock ran for over a year with no issue indoors keeping a GPS fix the whole time. After a power outage it wouldn't do anything more than count the hours since power on. Leaving the unit outside for hours with a clear view of the sky it still doesn't display a time. The PPS light is flashing after just a few minutes on the board and GPS module. Not sure if this is the right place for this question, Thanks in advance. ------------- |
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| mit | Posted: 5 Nov 2025, 11:34 AM |
 yeah whatever Admin Posts: 653 Joined: 4-May 16 |
If PPS is blinking, the GPS module is still working, so it's either that the connection between the GPS and Attiny is bad, or that the ATtiny is misbehaving somehow. It's possible that the power outage caused a spike that trashed the EEPROM on the Attiny. The first byte of EEPROM stores the calibration value for the RC oscillator. If it's way off, it may not be able to decoded the serial data at all. You could do a quick test to see if that's the case, by measuring how fast the clock is ticking. Look at the whole number of seconds after you power it up, and compare it to another clock or stopwatch. If it's off by more than 10%, that's probably the case. If it's ticking really slow, so slow you can see the hundredths of a second clearly, then it might be the fuse bytes (option bytes) got corrupted. In either case you need to re-flash the ATTiny. It might even be worth buying a new one and flashing that, if you think the power surge damaged it. Flashing a new one just means following the instructions here and also setting the fuse bytes, as described here. If you leave the EEPROM empty, it will use the default calibration, which is usually fine. ------------- |
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| kotor2knight | Posted: 6 Nov 2025, 06:52 PM |
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Member Posts: 4 Joined: 5-November 25 |
It gained about 2 minutes and 03 seconds over an hour. That's like 3% Ill get another ATtiny and program it fresh before i mess with the one on the clock. Want to make sure i get the correct AT. this one on digikey is readily available in my area. https://www.digikey.com/en/products/detail/microchip-technology/ATTINY2313-20PU/1008418 Thanks for the help, love the project!!!!!! ------------- |
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| mit | Posted: 6 Nov 2025, 08:50 PM |
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yeah whatever Admin Posts: 653 Joined: 4-May 16 |
Yep that's the correct part. Hmm, at 3% it should still be able to decode something. Might be some other aspect of it got fried. It could also be worth checking the continuity between the GPS module's TX pin and the RX pin of the attiny (labelled as GPS_DATA on the interactive viewer) ------------- |
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| kotor2knight | Posted: 6 Nov 2025, 10:07 PM |
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Member Posts: 4 Joined: 5-November 25 |
Good continuity between those two pins. I'll order that part from Digi and flash it. I put my crappy O scope on the RX pin on the micro and I'm seeing a burst of data about every second. Thanks for your help Mit!!!! ------------- |
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| kotor2knight | Posted: 25 Nov 2025, 01:04 AM |
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Member Posts: 4 Joined: 5-November 25 |
Fried the new MCU due to not looking at the pinout close enough flashed the MCU that came with my clock and it still just displays the count up. i flashed with the firmware as well as sending the code to set the fuses. ------------- |
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| mit | Posted: 26 Nov 2025, 12:57 PM |
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yeah whatever Admin Posts: 653 Joined: 4-May 16 |
Are you sure you fried the new one? They're pretty resilient outside of putting higher voltages into them. New chips are shipped with the DIV8 bit set, which drops the clock speed. If you try talking to it with avrdude and a slower speed it might work, add something like -B2000 to slow it right down. Once you set the fuse bytes it should then communicate at normal speed. With the old chip, you can try reading out the EEPROM data. The first byte of it is the oscillator calibration value. ------------- |
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