# Is inputting 12V to a 3.3V arduino inefficient or won't it matter?

So i have a arduino pro mini here is the schematic:

So looking at the board i can input between 3.35V and 12V to the board. I will use 4 CR2032 which are 3V(2V discharge voltage) each so 12V(8V discharge) in total. This is the cheapest for me, stores near me sell them for really cheap. But im a newb at the electronics. If i stack those 4 coins cell buttons on top of each other and input the 12V, will power get lost? Or does the board limit the voltage and draw less from the batteries?

Else i will have to look for solutions to get the power down from 12v to 3.3v, only if power gets lost.
I'm trying to keep this machine as small as possible. Thanks for your reading, hope someone can answer this question. I tried googling it but i didn't find a direct answer to this question.

On top of that i found out that you can power save the arduino with sleep functions and let the arduino for example use 0.84 mA instead of 15 mA, when the arduino only uses 0.84 mA will it only draw 0.84 mA, or much more than that?

Yes, using a 12V battery pack would waste a most of the power in that pack, given off as heat from the regulator.

You can power the Pro Mini from a single CR2032 through the Vcc pin. If you do, the Pro Mini should run at 8 MHz (use the 8 MHz internal clock).

In this case it is best to remove the power LED and regulator using a solder pencil, and carefully follow the suggestions in this tutorial on power saving.

It is very inefficient, because the Pro Mini uses a linear regulator, not a switching one.

If you must run it off of a coin cell, remove the voltage regulator and LEDs from the Pro Mini and download a custom core that will let you run slower than 8 MHz. I think MiniCore can do that. You will need something to use as the programmer though, like another Arduino board or a USBASP. Then you can power the controller directly from a single cell.

Depending on what you are doing and how aggressively you use the power-saving features, an ATmega328P can run for a very, very long time on a single coin cell. The deepest sleep mode sips only 100 nA typically, and could last well over a century on a 100 mAh battery.

Real battery life with a circuit that actually does something will obviously be far less, but it is not out of the question to get months or even years of operational life. However, effectively managing power is a significant undertaking in and of itself. You must plan how often and how deeply you can put the controller to sleep, how to wake it from sleep, and how to turn on and off the external parts of your circuit (if necessary).

All of this needs to be guided by the creation of a power budget, an accounting of all of the parts that use power, how much power they use, and how long they use it for. This lets you tackle the big fish first; if you've got some power LED that always on pissing away milliamps, there's no point in squeezing extra microamps out of your microcontroller. You can also use the budget to estimate how much battery life you can get per mAh of capacity.

Thank you both very much, i also have a 3.3v-6v screen connected but have decided to connect it to a separate power supply of 2 coin cells. And just connect the arduino to 1 coin cell and underclock it. I will remove the leds to save some power, and add a physical button to wake the arduino and also connect the 2 coins cell to the screen.
Another question if i connect 6V instead of 3V to a arduino will the arduino's battery life last longer or will the extra 3V all be just completely wasted?

If you have a 3.3V Pro Mini, then the voltage above 3.3V is "used up" as heat in the regulator.

dennis_arduinouser:
Thank you both very much, i also have a 3.3v-6v screen connected but have decided to connect it to a separate power supply of 2 coin cells. And just connect the arduino to 1 coin cell and underclock it. I will remove the leds to save some power, and add a physical button to wake the arduino and also connect the 2 coins cell to the screen.

What kind of display? A display might be a bit much to work off a coin cell.

Another question if i connect 6V instead of 3V to a arduino will the arduino's battery life last longer or will the extra 3V all be just completely wasted?

Higher voltage means higher current draw. Your battery life will be reduced.

Alright thanks for the help, ill just use less coin cell batteries. This is the display:

However connecting the VCC and ground pin to 2 coin cell batteries doesn’t work. (the other 2 pins are connected to the board for data)
It does work when connecting it to the 5V or 3.3V pin on my arduino and a ground pin.
Any ideas why it doesn’t work?

An LED display like that is definitely too much for a couple coin cells. They're meant for a couple hundred uAs of load, not many mA. Even if it could run, that display will drain the batteries flat in a few hours.

Thanks that actually isn't my biggest problem whenever i press a button i turn the display on for 5 seconds and then back of again so if the battery is drained in 1 hour with the screen on that isn't that big of a deal, 8 CR2032 cost 90 cents here. But the screen won't turn on at all when connecting the Vcc and ground to 2 coin cell or do i need to connect it straight to the arduino?

dennis_arduinouser:
So looking at the board i can input between 3.35V and 12V to the board. I will use 4 CR2032 which are 3V(2V discharge voltage) each so 12V(8V discharge) in total.

Stop there - CR2032 are typically good for 1 or 2mA current drain at most.

dennis_arduinouser:
Thanks that actually isn't my biggest problem whenever i press a button i turn the display on for 5 seconds and then back of again so if the battery is drained in 1 hour with the screen on that isn't that big of a deal, 8 CR2032 cost 90 cents here. But the screen won't turn on at all when connecting the Vcc and ground to 2 coin cell or do i need to connect it straight to the arduino?

The batteries can't produce enough current to power the display. Even if you wanted to use a capacitor, you'd need a beefy one. By my reckoning, for the voltage to drop 5% or less with a 5 second draw of 10 mA (probably low-balling the current usage of the display), you'd need 0.5 F. That's regular farads, not milli-, micro-, or nano-.

Coin cell batteries are meant for applications that use very little current. They are unsuitable for an OLED display.

Thanks for the replys but after trying to use the vin and ground pin i got it to work with 2 coin cell batteries or 3 aaa batteries.
One thing i dont fully understand the power consumption for example i connect 2 coin cell (3V 190mAh each) to the arduino. And i do some things like removing leds and set it to 8mhz to let the arduino only consume 4mah instead of 16mah will it actually draw less from the batteries or wil the power consumption always be the same no matter if a screen is attached? Since the 2 batteries input 6V.

Firstly you are confusing current (measured in A and mA) with charge (measured in Ah, mAh or C). They
are not the same thing.

The symbol for amp is 'A', not 'a' which means atto.

You question seems confused - if you reduce power consumption less power is consumed. Screens consume
power too.

And remember those 3.0V lithium coin cells are only able to handle about 1 or 2mA. Use 1.5V alkaline
button cells or a small LiPo if you need more current.

I actually got the arduino and screen to work of 1 coin cell button it doenst have a pin13 led so that saves me some work. Im still confused, if i use 2 batteries which are both 200 mah in power size, does the aruiduno last twice as long or just a little longer in overal? Thanks ill run a test now with 1 coin cell to see how long it will last. Thanks for explaining things out!