Placing decoupling capacitors when building an Arduino PCB with Atmega328-PU

Question

I have previously asked this question:

Custom build of arduino on a pcb

And thanks to the answer by Majenco I have learned that my circuit works a lot better when adding a capacitor. For example I am using the NRF24L01 and it is much more stable when using a capacitor. I am placing the capacitor for now next to the power supply like this:

enter image description here

Right now I am running this on a breadboard. The Atmega328 chip is very cheap compared to the arduino uno board; therefore, I will like to continue building my projects based on the atmega328P-PU chip.

Anyways before printing the PCB based on the Atmega328P-PU chip, where should I place the capacitors in order to reduce the most noise? The capacitors are very cheap and making one good design will enable me for all my future designs to be based from this one.

From researching on the internet I see a lot of different examples. Everyone uses different capacitance sizes. For example I have found this:

enter image description here I got that from this link: https://www.autodesk.com/products/eagle/blog/what-are-decoupling-capacitors/

On other places they say to place the capacitance closest to the pins such as from this video. If that is true should I just place one capacitor on pins 7 and 8. Lastly the other capacitor on pins 20 and 22?

I do not mind soldering extra pins knowing my circuit will have the best performance.

• hcheung: There is a reason that many chip has VCC and GND next to each other or nearby. You should place the capacitors close to those pins, for both VCC and AVCC. Read the datasheet as it provide much more information.

Answer 1

The Autodesk link explains it very well.

You should place small/fast decoupling capacitors (0.1uF) close to the power pins of your on-board ICs to deal with local spikes in power consumption of those devices.

Place a larger/slower decoupling capacitor (1uF or larger, depending on many factors such as distance of the power supply from the board and expected power consumption) somewhere on the board to deal with varying loads and ripples in your power supply.

This has been common practice at least since I’ve started with electronics about 40 years ago (and probably much longer).