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Topic: Where do these caps go? (Read 961 times)previous topic - next topic

mikecurry

Feb 08, 2011, 02:53 am
I can't figure out how to place these capacitors?  (the two by the 5v regulator)

Any help would be appreciated.

Here is the big image: http://itp.nyu.edu/physcomp/uploads/arduinobb_07.jpg

James C4S

#1
Feb 08, 2011, 03:01 am
The negative of a polarized capacitor is going to be connected to ground.  So the capacitor on the right is connected to the positive (red) and negative / GND (black) rails of the breadboard.

The one of the left shares the GND pin of the regulator which looks to be the middle pin.  So the cap on the left will connect across the VIN and GND of the regulator.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

mikecurry

#2
Feb 08, 2011, 03:43 am

The negative of a polarized capacitor is going to be connected to ground.  So the capacitor on the right is connected to the positive (red) and negative / GND (black) rails of the breadboard.

The one of the left shares the GND pin of the regulator which looks to be the middle pin.  So the cap on the left will connect across the VIN and GND of the regulator.

Ok cool, thanks!  But how come the capacitor goes from + to - in both cases?  I don't see the reasoning, what is the purpose of doing that?

James C4S

#3
Feb 08, 2011, 03:57 am
One provides de-coupling on the regulated 5v side, the other provides de-coupling on the unregulated side.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

Bill_Kerr

#4
Feb 12, 2011, 03:07 am
Hi Mike

Sometimes a picture is worth a 1000 words, check out
http://artengine.ca/~pflemming/flemmweb_current/schem/opamp_linear/7805.pdf
this should give you a good idea of the connections

I would also suggest adding a .1uF ceramic capacitor on the output pin to GND.  This will sometimes prevent high frequency oscillation on the output voltage.  It is reccommended on the spec sheets.  I have only seen the oscillation once, but it caused me grief not having it, so I now just add it.

A ceramic capacitor has no + or - orientation.

Regards  Bill
Don't you just hate ONE D 10 T problems?

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