# 100 nF capacitor between Arduini VIN and GND?

Hi! I'm using an Arduino Nano in a breadboard circuit. The Nano is power supplied by a 12 V battery. I was wondering if it is better to place a 100nF capacitor between GND and VIN, in order to assure stability to the circuit. Thanks.
Valerio

I typically like a filter cap like that on the input but I usually parallel it with a .1ufd ceramic cap to cut the high frequency stuff. In an ideal world, the 100nf would also take out high frequencies, but in the real world, the internal features of the 100nf cap (including lead inductance etc.) cause it to act more like an open at high frequencies (which is why you will often see schematics drawn with both electrolytics and ceramic caps in parallel).

mmm... I'm a little bit confused with values: 100 nF and 0.1uF should be the same values, am I right (100 nF = 100*0.001= 0.1 uF)?
If I understand, you are suggesting to use two capacitors with the same value in parallel, the first ceramic (100nF), the second electrolitic (0.1nF), because of their different features. Is it right?
Thanks a lot!

100 nF and 0.1uF should be the same values,

Yes I think that was a typo an 100nF should have been 100uF.

Sorry, my bad - I still miss the "nf" - I am used to ufd and uufd (I'm really old !! - think vacuum tubes :o ). Typically, I would have some sort of electrolytic - say 47ufd on the input with the 0.1ufd (or 100nf) in parallel with it. The comment about "ideal" vs "real world" is still valid though - the ideal value of reactance for a capacitor vs frequency should approach 0 as the frequency goes up, but in reality, many of the larger capacitors (electrolytics etc.) look more like a bandpass with a big dip in the middle and then the reactance goes back up again as the frequency goes up into the mhz and above range.

You state that Vin is 12V, and you've got it powering an Arduino Nano on breadboard.

The Arduino Nano contains an on-board regulator, but strangely, there doesn't appear to be an input capacitor on said regulator. LDO regulators normally want a cap on the input. Most want something like 4.7~22uf on the input, and may be picky about what kind of cap it is.

However, since most Nano's in circulation are clones now (the design is discontinued by Arduino), they're not all the same... a quick look at nano's on ebay showed that some of them have more caps than the official design had on them (on the first design I looked at on ebay, I counted 9 vs 7 on the official ones. One of the caps was very clearly an input cap on the regulator, which was also a different regulator than the one the official board uses (I suspect the other "extra" cap was an extra 0.1uf decoupling cap)

So... What I'd do is:

Look at the Nano, and follow the trace from the Vin pin (using multimeter in continuity mode is easiest) and see if it's already got an input cap on the board.

If it doesn't, identify the regulator, google the part number to get the datasheet. See what it says about input caps (regulator datasheets almost invariably have a section about input and output caps), and add a cap consistent with those specifications.
If it does include a cap, you're good on that front.

Either way, if you're concerned about the stability of the 12v supply, or the leads going from supply to breadboard are too long, you can go ahead and put a larger cap across Vin too.

gpsmikey:
Sorry, my bad - I still miss the "nf" - I am used to ufd and uufd (I'm really old !! - think vacuum tubes :o ). Typically, I would have some sort of electrolytic - say 47ufd on the input with the 0.1ufd (or 100nf) in parallel with it. The comment about "ideal" vs "real world" is still valid though - the ideal value of reactance for a capacitor vs frequency should approach 0 as the frequency goes up, but in reality, many of the larger capacitors (electrolytics etc.) look more like a bandpass with a big dip in the middle and then the reactance goes back up again as the frequency goes up into the mhz and above range.

The symbol for the farad is F, not f, f is not an SI unit, it is a multplier (femto). Yes the unit is called 'farad'
despite being named after Mr Farad. That's how SI is, its all very well explained and documented and standard.
Learn it!

I didn't say it wasn't a standard, I said I missed it - there is a difference.