Measurement of Bandgap voltage

[retrolefty]

Cool, something to play with tonight.

So is the purpose of this so that the A/D conversion is performed in a quieter condition then normal non-sleeping condition? I have noticed that on the code I've posted that if I perform just one read of the bandgap voltage it has not settled down to a stable count value. Three reads is OK, within a count or two, and four has the same stable count reading that stays the same no matter how long the function continues. I recall reading in the datasheet about having to perform multiple A/D conversions before obtaining a stable reading, but I thought that was only when changing voltage references, which I'm not doing?

Again thanks for posting the code.

Lefty

[Coding Badly]

So is the purpose of this so that the A/D conversion is performed in a quieter condition then normal non-sleeping condition?

Exactly.  I've notice some difference on the ATmega processors.  There seems to be less jitter in the least-significant bit.  I've noticed a huge difference on the ATtiny processors.  The values are rather erratic in "polling mode" but rock solid in "noise reduction mode".

I have noticed that on the code I've posted that if I perform just one read of the bandgap voltage it has not settled down to a stable count value.

My 168 and 328 processors behave the same way.  The first reading after switching ADMUX to "measure the bandgap" is garbage.

Three reads is OK, within a count or two, and four has the same stable count reading that stays the same no matter how long the function continues.

About the same here.  I usually have a short time delay between readings so, in my case, the readings are stable by the third one.