At AREF, it's just decoupling capacitor as in the datasheet... Anyway, I am not using the AD...
Maybe it's not the charging that makes it stop... I thought that was the reason, cause when I saw it discharged, the circuit worked again... it doesn't work too long by the way
Are you sure the cap is connected to where you think it is? What does the cap charge up to when it stops working?
Once VCC is over ~3.9 volts, the processor should just run, and if it continues to 5V it should not make a difference.
If the power supply has enough current, the cap should charge up almost immediately if it is actually connected to VCC.
the atmega, the 100n caps and the shift registers are smd... the capacitor itself is pth
I'm starting to think that the behavior after I discharge the capacitor is just a coincidence, and it's charging is not actually the reason of the problem...
Still it is difficult to explain this issue besides faulty wiring. Other than that I would check reset, power (including brown-out detection) and clock.
Stupid question, can you take the capacitor out of the circuit? Or change the program you're using to troubleshoot the problem?
If you're not sure if it's the capacitor or the software, changing one of them would be enough to determine that. Also, what's the voltage on the capacitor pins once it finishes charging?
I don't think the capacitor is defective, as I switched it and the problem wasn't solved...
bubulindo, I took the capacitor out of the circuit, and the problem never happened again. I'm just trying to understand what happend, so I don't make the same mistake again.
BenF, I also don't think that wiring problem. I soldered it, but it's a manucfatured board. Reset is right, and the brown-out detection is disabled. Also, I checked the 3v3 line after the system got stuck, and it's just fine... fixed at 3v3
And when it gets to 3.3V the circuit stops working? Watch it with a scope - does it ramp up smoothly, or does it look to have some switching noise or something on it?
That sounds like a really crappy power supply, or there is some other signal connected in.
What are you using for a power source?
With that size cap, it should be a lot smoother.
I might be getting somewhere in the other forum (avr-freaks: http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=104717&postdays=0&postorder=asc)... There was a suggestion that maybe my capacitor (which probably has relativelly high ESR) is introducing noise to the supply source with the raise of both the output capacitance and ESR for the supply source with the extra capacitor inserted.
CrossRoads, I'm using a L5973D based circuit using the 12V of a regular computer power supply. I'm getting a ripple of around 100mV...
brenin:
I have a circuit and when I put a big capacitor (330uF) near the atmega, the atmega gets stuck after running for a while. When I discharge the capacitor the circuit works again for a while and then stops again. On oscylloscope, i saw that the circuit stops working after the capacitor charges.
I don't understand this bit. Until the capacitor charges, the processor does not have full VCC voltage, right? So it shouldn't be working before it charges. And you are saying it doesn't work after it charges. So it doesn't work at all, basically?
What the capacitor might be doing is confusing the processor with a slow VCC ramp-up. At a certain threshold the processor detects that VCC is high enough and initiates reset processing. But the very act of doing this causes extra power consumption (eg. pull-up resistors) which drops VCC down below operating voltage. The processor might be confused.
What might help is a capacitor/resistor on the reset pin that delays reset processing slightly.
brenin:
As i pondered before, it was more like a coincidence that the circuit stopped working and it worked again when I discharged the capacitor.
It stops working long time after the capacitor charges completelly... It has a ripple noise of around 100mV... There are also some 300mV spikes..
[quote author=Nick Gammon link=topic=55711]
I don't understand this bit. Until the capacitor charges, the processor does not have full VCC voltage, right? So it shouldn't be working before it charges. And you are saying it doesn't work after it charges. So it doesn't work at all, basically?[/quote]
The circuit works after the capacitor is charged... It actually charges pretty fast, much faster then the time needed to get stuck...
What happens is that it stop working after running for some time (i.e hours on the first time it happens and up to minutes on the following occurrences)