Power sensor? Battery?

[CrankyCoder]

I have my first sensor built and ready to go into it's final casing. However, I am trying to power it via batteries. Was hoping to get away with some AAA batteries.

Would I be better off using 2 AAA batteries and stepping up the voltage to the 5v my pro mini needs? Would I need a second step up converter to get the 3.3v for my nrf24l01? Or should I power it with 4 AAA batteries and bring it down to 5v and 3.3v? Or should I get a 3.3 pro mini and just bring voltage up or down to 3.3v for both the pro mini and nrf?

So many options

Just looking for some feed back and suggestions

[mfalkvidd]

Get a pro mini 3.3V and remove the power led and regulator. Power the Arduino and the nrf directly from 2xAA/AAA. See https://www.mysensors.org/build/battery for how & why.

[alexsh1]

I complete agree with @mfalkvidd. Every time you boost or step down voltage, you waist some energy. Besides, why would you need to boost to 5v as additionally you will have to step down voltage to 3.3v for radio? Not logical.

3.3V is the best to be used for low power devices. Just make sure you disable
BOD via avrdude and you can have optiboot to get more space for sketches. This is optional.

[CrankyCoder]

Sigh, i was afraid that was going to be the answer lol. I don't have any 3.3v mini's laying around. Oh well, time to order a batch.

Thanks guys. Very excited to have my first sensor built and ready to get it mounted on the wall.

[m26872]

@Jason-Brunk Since it's your first sensor you better buy some 3.3V pro minis. Later on you'll probably want to learn to deal with bootloader and fuses, then you could have reused your 5V pro minis as 3.3Vs.

[CrankyCoder]

That looks interesting. I have saved that for some later reading thanks!

[NeverDie]

@Jason-Brunk
You can run a 5vpro mini at 3.3v if you remove the voltage regulator. Technically, it's out of spec for 16Mhz, but I have yet to hear that it has caused anyone problems.

[alexsh1]

@NeverDie I would not run 16Mhz at 3.3V as this would be unstable - however, running a 8Mhz bootloader is just fine.

I have a couple of 5V Pro mini which I am using with older 5V sensors.

[NeverDie]

@alexsh1
Moteinos run the atmega328p at 16Mhz at 3.3v. What's the difference?

[alexsh1]

@NeverDie I actually have a Moteino Mega on order so we can discuss it after I'll give it a spin

However, looking at atmega datasheet, it states that the chip is only specified at 10MHz with 3.3V supply. I know a few people who run it at 16Mhz with 2xAA batteries just fine, but given that I do not extra 8Mhz and much more in favour of stability, the choice is obvious.

[NeverDie]

@alexsh1
The Moteino Mega isn't based on the atmega328p though, so it won't really be relevant to this. Did you mean a Moteino R4?

[alexsh1]

@NeverDie Yes, you are correct - it is based on ATMega1284P. So not relevant

My point is that I'd rather stick to the datasheet rather than overclock, but that's just me. And yes I realise that Moteino is overclocking, but the size, voltage and flash are really appealing to me.