What's the difference between these two capacitor wirings?

As I understand it from other threads, C1 would be a decoupling capacitor; when there’s a dip in VCC, C1 makes sure to compensate for it thus providing IC1 with a stable voltage. On the other hand, I’ve also seen capacitors like C2 all over the place but I’m not entirely sure why they are wired like that.

What’s the difference between these two?

PS: I’ve picked a random IC from eagle for this schematic just as an example.

On the other hand, I've also seen capacitors like C2 all over the place but I'm not entirely sure why they are wired like that.

Really? Do you have an example?

I've seen those wired to ground like that, and not connected to VCC but some other pin where it just needs a capacitor to ground. #1 is far more common and actually useful.

What’s the difference between these two?

Simplified, a capacitor is a barrier for DC and a pass through for AC.
C1 acts as a buffer, so that one is understood correct.
C2 is an AC pass through, and will never be used as drawn (to a power supply connection).
One would connect one side a a capacitor to some signal and the other pin to some input connection if one wants to make sure they are only receiving AC signals.

Read AC as continuously changing levels in this case.

Again this is very simplified, and there’s much more to be said about this.

Thanks for the prompt reply. As I was learning to make my breadboard prototypes into PCBs I found this eagle schematic online (see C7 and C9 in the attachment). I’ve used it to build a few PCBs without problems but these capacitors always intrigued me.

I’ve seen this also in guitar pedal schematics where (as MAS3) mentions they were dealing with audio signals and it makes sense that they would want to block DC. Still it puzzles me , if what you say is true, how they were working in the attached schematics. In all the PCBs I made with this -not many- the VCC pin had 5V even with the “DC blocking” caps. But again, I might be measuring things wrong since I’m pretty new at this.

Sorry that schematic is absolute rubbish. The capacitors on those power pins C7 and C9 are all wrong and would prevent the chip from getting a proper supply. A circuit built like that would not work correctly.

The caps on the crystal are correct however. I have no idea where the one on the reset goes but that looks wrong as well.

Mike, thanks for your reply. The other end of that cap goes to an FTDI pin. Here’s the other part of the screenshot.

In that case C5 is correct. It resets the Arduino whenever a serial connection is initiated.

The caps in the VCC and AVCC lines just are wrong, the controller will not be powered this way.

All Vcc pins on the chip must be connected together, and AVcc must be either connected to Vcc or kept within 0.3V of Vcc. That diagram is broken.