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I am building a circuit based on an ATmega328P. In the schematic of the datasheet are 3 capacitors (1uF, 4.7uF polarized, 1uF) in parallel on the power supply Vcc. I assume these are for decoupling purpose.

snippet from schematic diagram

I currently only have 470nF ceramic film capacitors (805) and tantalum capacitors (805). Is it possible to connect 2x470nF in parallel to achieve the ~1uF on the respective lines? In theory the capacitance is 940nF, but since it is used for decoupling it might be bad for the signal, because I solder two parts instead of one (more solder, cables, cable length, more resistance, ...).

Does this matter in a practical situation?

EDIT: I build the circuit on a hole grid breadboard

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    \$\begingroup\$ Do not forget that capacitors add in parallel and not in series. \$\endgroup\$ – Wheatley Oct 31 '19 at 9:02
  • \$\begingroup\$ My mistake. I changed it the desired situation. Thanks \$\endgroup\$ – v3xX Oct 31 '19 at 9:07
  • \$\begingroup\$ However, I think it does not really matter. A simple 470nF shoud be enough because your microcontroller does not draw a lot of current. \$\endgroup\$ – Wheatley Oct 31 '19 at 9:08
  • \$\begingroup\$ The VCC and AVCC pins should be decoupled independently, they are very far away from each other: place a small cap (10–100 nF) close to each supply pin. \$\endgroup\$ – Marcus Müller Oct 31 '19 at 9:14
  • \$\begingroup\$ As a courtesy and good practice, please have your decoupling capacitors facing up/down and ground pointing downwards. Drawing common circuit elements in an unusual way obfuscates the meaning of your circuit, which defeats the entire purpose of the schematic. \$\endgroup\$ – BB ON Oct 31 '19 at 15:28
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Does this matter in a practical situation?

NO, one capacitor of more than 100 nF is usually already enough in 99.99% of all situations.

Place the capacitor as close to the VCC pins as possible.

There is really no need to place more than one 1 uF ceramic capacitor.

There is no point to combine decoupling or bypass capacitors such that they have a certain value.

Learn more about bypass capacitors by watching the EEVBlog video on the subject.

EDIT: I build the circuit on a hole grid breadboard

When using a breadboard, connections are so bad (due to contact resistance) anyway that it really doesn't matter what capacitor values you use.

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  • \$\begingroup\$ Why are there 3 capacitors in the datasheet? And explicit a polarized one? They must have some function \$\endgroup\$ – v3xX Oct 31 '19 at 9:10
  • \$\begingroup\$ When the circuit is working I will commission a PCB where the connections are much better \$\endgroup\$ – v3xX Oct 31 '19 at 9:14
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    \$\begingroup\$ @v3xX Either inexperienced designer or that is the only Vcc bulk capacitor on the board. If the latter, you should avoid drawing like that to avoid these questions. \$\endgroup\$ – winny Oct 31 '19 at 9:16
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    \$\begingroup\$ Why are there 3 capacitors in the datasheet? Because the chip has 3 VCC/AVCC pins each pin gets its own capacitor. The polarized capacitor has a larger value and also a "buffer" for energy. A non-polarized capacitor with the same capacitance is larger and more expensive. There are many things that (experienced) designers do in certain ways because these ways have been proven to work. Just follow their lead, do what they do. You might not always fully understand but that does not matter. Your circuit is non-critical, add a capacitor here and there and it will just work. \$\endgroup\$ – Bimpelrekkie Oct 31 '19 at 9:25
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    \$\begingroup\$ Yes that is the correct approach. \$\endgroup\$ – Bimpelrekkie Oct 31 '19 at 9:33

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