Buck converters tried out.

With a 7805 I think it takes at least 7V input to get a steady 5V out?

I put 5.2V measured into a DC-DC converter and got a solid 5.0V out. Then dialed down to 3.3V which is loosening the adjustment screw a lot of turns. It goes lower.

This is all supposed to be over 90% efficient. What was lost to heat with 78XX regulators is most all converted to more output current instead. A 9V battery loses 45% current going through a 7805. 9V on Arduino has been disappointing before. With a buck converter, the 9V will deliver almost 80% more than through the 7805. 6V would also work too where a 7805 needs 7+V and 6V would be voltage divided to get 5V plus heat, now it's 5V plus more current and some warmth.

Next, I buy boost converters. Run an Arduino UNO from a AAA or button cell or small alternate energy source. AVR don't eat much. Not to blink a led.

Indeed, they do exactly what it says on the packet ;) One thing to avoid is overload: try to take too much current and switching converters normally shutdown immediately, and/or refuse to start up.

For sensitive analog circuitry (microphone amplifier for instance) always use a linear regulator, the noise generated by switching is significant for such circuitry.

Ya man, DC/DC converters are great. You can get (slightly shoddy) ones on ebay for insanely low prices, too.

They do have higher quintescent current than linear regulators (as you might expect).

On the topic of overloads, make sure you know how your converters will react to an overload or short circuit. Some react gracefully - but others (of course, the cheaper chinese ones) just fail, sometimes spectacularly.

I've managed to accidentally short out three of these http://www.ebay.com/itm/181409861491 (no vendor endorsement) Even the briefest short will reward you with a brief flame from the left side of the chip near the pins and some foul smelling smoke. Not that that stops me from using them, but I know I have to be more careful with them.

The DC-DC converters need indeed a larger current. I have one that uses 15mA for doing nothing (nothing at the output). That is something to keep in mind when using batteries.

By the way, I think that a 7805 is too noisy for a mic pre-amplifier. The noise from zenerdiodes and transisotr is hard to remove. Decoupling capacitors is not enough.

DrAzzy, thanks for the warning. In my projects I have good converters, but I did buy those cheap ones. I better not use them then.

I'll just try and use half or less of the maximums, same as I would with Arduino pins.

Mostly this is a head's up for those who haven't used converters. They're out there and they're neat.