What is the purpose of this capacitor ?

Hello,

I have many arduino nano board without this capacitor (broken, unsoldered). Is this capacitor is important in the operation of the arduino ? Or the arduino can work properly without it ?

Thank you.

This picture says it's probably the AREF capacitor, which is only needed for "better noise performance" when using the ADC converter. OTOH, it's a "compatible" rather than an official Nano, so you'd have to ask the vendor for design documents (hah!) or trace it out to be sure. My Nano compatibles look entirely different.

It seems that this is it !
I use the 3.3v to power RFID sensors, es that it will alter their smooth operation?

RFID sensors tend to be digital. A missing AREF cap shouldn’t bother them. (I can’t tell for sure without knowing which RFID sensor, and researching its datasheet/etc.) And of course, if your boards have those caps ripped off by physical damage, who knows what else could be wrong.

They are arduino recover from old circuits, the extraction method caused the loss of this capacitor. I do not think there are other problems.

Thank you very much !

westfw:
RFID sensors tend to be digital. A missing AREF cap shouldn’t bother them. (I can’t tell for sure without knowing which RFID sensor, and researching its datasheet/etc.) And of course, if your boards have those caps ripped off by physical damage, who knows what else could be wrong.

Missing the AREF decoupling cap will cause the ADC readings to fall well out of specification I suspect, ie
significant amounts of cross-talk, noise, etc on readings. If this matters a 100nF ceramic capacitor should be
soldered back onto the pads.

But as the AREF is probably connected direct to Vcc anyway, it may behave OK if Vcc is relatively clean
and well decoupled itself.

There is already a 1000µF capacitor on the power line of my circuit board. I think it will be okay.