How to get a constant 5V output regardless of input voltage?

[Saylor]

Hi there. I'm an absolute electronics newbie and I've just recently started designing some toys using the arduino IC atmega328p-pu. It's the great new hobby I was looking for. But I've run into a little problem:
As I understand it, the IC needs a constant voltage of 5V to operate properly, anything lower than that will trigger the internal brownout detectors and the device resets.
Since I want my little toy to be portable, I decided to power it using two CR2450 cells, giving me an initial voltage of 6V. So initially, I have to lower this voltage to 5V to operate the IC. But as the battery voltage drops, my output voltage needs to stay the same. So, in essence, I need a magic circuit which takes whatever input voltage from 6V to 1.5V or however far the cells discharge and outputs a constant and relatively stable 5V to power the IC.

What would be the proper way of doing this? I understand some things about buck converters to raise the voltage and some things about the 7805 voltage regulator to lower the voltage but I need a device or circuit that does both. Thanks for your help!

 

[Arouse1973]

Hello. A buck boost regulator is what you need. You will find many on the net. Let us know if you need any help.
Thanks
Adam

 

[Audioguru]

Your two CR2450 cells in series produce about 6.4V when new and about 4.8V when run down.
The datasheet of a 7805 voltage regulator says its minimum input is 7V so you cannot use it. A "low dropout" 5V regulator minimum input voltage is about 5.2V.

 

[biosonar1]

Just a word word advice, make sure the IC you select for your regulator is not obsolete. You can find lots of circuits on the web that are from various archives that use components that just can't be had easily (except from China, but be careful they can be counterfeit).