I have a very simple design that I'm now working on the PCB layout for. And at the moment I'm thinking about the issue of decoupling capacitors. The board is very simple and only consists of this:
1 x ATtiny85 3 x resistors 1 x 32.768 kHz crystal 2 x 22 pF caps for crystal 3 x LED
The board is powered by 2xAAA batteries. The MCU is clocked at 32.768 kHz by the crystal.
So as you can imagine it's just a real-time clock with some additional logging functions. Now, the question is this: Do I need decoupling capacitors for this circuit? If so, do I place them:
1. Between the Vcc and GND pins of the ATtiny, close to the ATtiny 2. Between the Vcc and GND traces, close to the battery 3. BOTH of those, i.e. use two capacitors, one close to the MCU and one close to the battery
...or can I simply ignore decoupling caps for a circuit as simple as this? And do you have any advice on which capacitance to use for the decoupling caps?
Also, if I do need decoupling caps, it would be great if someone could explain the advantage of them. I.e. do they help improve the stability of the real-time clock? Do batteries normally have voltage dips in certain circumstances?