7805 voltage regulator to power standalone atmega328

Hey fellas,

I am in the process of running the atmega328 from my duemillanove as a standalone and for power I am using a 12v source, so I got myself a 7805 voltage regulator. My question is, can I connect the 5v output from the regulator to the power pin on the atmega, or its there some "softening" to do before? i.e using capacitors.

Kind Regards,


All digital chips need de-coupling capacitors. All voltage regulators need de-coupling capacitors.

The datasheets tell you how much (or how to determine how much).

General information from Grumpy Mike: De-coupling

Here's my alarm clock which uses a 7805 regulator:

I use the documented capacitors for the voltage regulator, and the decoupling capacitors James mentions. Apart from that, you can connect to the output to the Vcc pin of the Atmega.

can I connect the 5v output from the regulator to the power pin on the atmega,

Yes, you can.

Many regulators require some input & output capacitance to avoid oscillation. Some don't:

"Considerable effort was expanded to make the LM78XX series of regulators easy to use and minimize the
number of external components. It is not necessary to bypass the output, although this does improve transient
response. Input bypassing is needed only if the regulator is located far from the filter capacitor of the power

Putting a 1uF on the input and 0.33uF on the output certainly won't hurt anything. I usually put a 10uF and 1uF on if I have them handy, or values in that ballpark, and then 0.1uF on the Vcc pin of every part.

Here's my alarm clock which uses a 7805 regulator

Will be useful as a clock if using a crystal as shown, or a Duemilanove [which "apparently"
also uses a crystal], but not when using a ceramic resonator or a UNO board, which appears
to use a resonator and not a crystal. Crystal = 20-50 PPM tolerance, resonator = 0.5%

Here's the full project: Gammon Forum : Electronics : Microprocessors : Alarm clock from Atmega328 and 7-segment display

It has a DS1307 clock chip, so the processor clock accuracy is not of great importance.