Powering the Atmega328p

Hi guys.

I have an Atmega328p that will be in use for 3 days in a year. An hour a day, but with delays. Not more than a minute in a row. So I made it with batteries. Two cr2032 to be precise. Those batteries gave 6V which is a little much for that MCU.

I made a similar with the same components a few years ago. Pro Mini runs two years with 2 cr2032. But, is there a better solution, than LDO? Those batteries quickly go down to 2,7V so it is only for initial days.

Some say to use LDO after all, some to use Zener. What do you guys say?

The chip can run on as little as 1.8volt with the right clock and fuse settings.
What does it have to do. Can't you use a single CR2032?
Did you read Nick Gammon's low power pages?
Leo..

I have an Oled display and a few things that need 5V, though Oled has its LDO. I just need a solution for those 6V to low a bit. It will not be in use for a long period of time, but when in use those 30 secs or a minute, it needs to work as it should. So, basically, any on the fly solution will do the job. I am much to Zener, say, BZV55C 5V1.

But as I am not sure...

I have an Atmega328p that will be in use for 3 days in a year. An hour a day, but with delays. Not more than a minute in a row

There's nothing here to suggest it is going to powered on the other 362 days of the year. Is that correct ?
You will switch it on and off as needed but that is only three days in the year , right ?

Pro Mini runs two years with 2 cr2032

How many days was it on during those two years ?

It will work say, 5 days a year MAX. On batteries. And on that one day, it will work some 30 sec, with delays of half an hour or so. It will be powered up with a switch.
As I said, I have something I made with 2 CR2032. It works for years. I didn't say it won't damage MCU.
I don't care if I have to change batteries every year. Just to make it work that small amount of time, without a hassle.

I don't believe that it will work for more than 30 min on a yearly basis. Maybe less.

It will work say, 5 days a year MAX

As I said, I have something I made with 2 CR2032. It works for years.

Which is it ? 5 days or 'years'. If by years, you mean the shelf life of the batteries all that time it is off and not being
used ? Or do you mean you can leave it on for years. I think you mean the former and not the latter.

Mate, it will stay shut down for centuries.
It will work damn little. Not much to care about. Forget about it, please.

Question is:
How to drop 6V just a little bit? I think 5,5V will do the job. Although, batteries will drop a little so it ain't make a big problem.

Just use a 1N4001 diode between the batteries and the ATMega328 (anode on battery side, cathode (banded end)
on MCU side.) That will drop it 0.5 to 0.7V.
6-0-0.7=5.3V. ATMega325 can tollerate up to 5.5V, mate.

IIRC ATMega have 6.0 V abs max.
But some Lithium coins have more than 3.0 V.
I doubt a diode will drop 0.5V with current in order of uAs.
This is work for a low quiescent current LDO such as HT7550. Or even better: single cell.

EDIT: I just measured forward voltage drop of a Zener diode (I did not find "normal" silicon diode quickly enough). The forward drop was over 0.5 V down to about 0.5 uA (at room temperature). Using one or two diodes to drop the voltage may be reasonably safe after all.

Very informative ! Looks like the OP only needs one battery.. I actually did the same thing once with a
2x16 LCD. I think I got down to about 2V. That was
about five years ago. I had completely forgotten until I saw this.

I just measured forward voltage drop of a Zener diode (I did not find “normal” silicon diode quickly enough). The forward drop was over 0.5 V down to about 0.5 uA (at room temperature). Using one or two diodes to drop the voltage may be reasonably safe after all.

I just measured the voltage drop of a 1n4001 diode at 50uA and it was 0.3874V.
Circuit:
Vcc=3.00V
Vcc to diode to 1.5k + 91k to GND
V1N4001=0.3874V

54 μA
Using an Arduino Pro Mini, with a simple modification, the power consumption goes down to 54 μA (0.054 mA) with the 3.3 V version or 23 μA (0.023 mA) with the 5 V version, in power-down sleep. That is 4 years on a 9 V battery with 1,200 mAh capacity or 2,000 times more efficient than the Arduino Uno.

Can 1n4007 do the job?

A 1N4007 is merely a higher grade of 1N4001, rated to withstand 1000 Volts rather than just 50. the current rating is the same.

For less than 100 mA, a 1N914 will even do!