one battery to power both Arduino and a servo motor

what i’m trying to achieve basically is the thing in the photo.
so i have:

  • arduino that runs at 3.3v link
  • a servo motor (low energy)
  • a 6600 mA battery pack link
  • a NRF24L01+ link

i need this to be a low energy project that has to run at least months, any suggestions are welcomed and the easiest way too.
i’m open minded to any other ways to do this, i thought that one battery is better (because i’d have to buy another battery and perhaps that battery runs out quickly) but maybe i’m wrong, tell me.

the big project is that this one have to unlock an external door (by pushing a little metal thing inside an electric lock - it doesn’t need a lot of pressure) activated by another arduino inside the house that sends a signal with another nRF24L01+.


Some thoughts for your digestion 1. How are you going to get a rotary motion to translate into whatever motion is required to push the lock thingy? Would a solenoid be better?

  1. What does 'turn the servo' do (e.g. switch motor on/off at full power?).

  2. Motor load might pull the battery down below the minimum voltage for the pro-mini, which may then malfunction. Suggest you use a higher voltage battery, then use that to power both motor and a voltage regulator for the PM board.

yendis: Suggest you use a higher voltage battery, then use that to power both motor and a voltage regulator for the PM board.

I agree with yendis.

Not many servos will work properly with a voltage supply from a single LiPo/Li-Ion cell.

I can think of three options to get your project working.

  1. As yendis suggests, use a higher voltage supply and a regulator to power the Arduino. The problem with this option is you might need a regulator for the servo. Most servos aren't happy with voltage levels from either a single LiPo cell or the voltage from two LiPo cells. If you use a 2S LiPo/Li-Ion you'll likely need a regulator for the servo.

  2. Purchase a servo which will operate powered from a single cell.

  3. (Probably my favorite for this application.) Use a boost converter for the servo. There are lots of boost converters on ebay. Depending on how much current your servo draws, you may get a way with using one like this. If your servo is a full sized servo, you'll probably need a boost converter capable of higher current.

Whenever I purchase cheap ebay parts, I usually get a couple extra in case one of the parts doesn't work.

Adafruit sells several nice boost converters.

If you want to find a servo capable of being powered from a single cell, let us know and we can try to help you find one.

ianofgod: - a servo motor (low energy)

A link to the servo you're using would be helpful.

I don't think I'm the only one who thinks "a servo motor (low energy)" is an oxymoron.

Have you measured the force required to push the lock mechanism?

You might be better off buying a battery operated keypad door lock and modifying it. They have low power mechanisms that will run for a year or two between battery changes. That would be very difficult to achieve with a hobby servo.

thanks to all the reply,


those were simple schematics, the idea was like you’ve said, use a power booster to change the voltage from 3.7 to 5v so that any kind of servo is good.

the servo just need to rotate for some degrees and then it will touch a metal thing that does all the work, i didn’t thought about a solenoid because it would run on more Volts and needs another battery or a stepup regulator (which indeed runs out the battery quickly). the thing that the servo has to move is the one in this photo:


i was worried that the circuit didn’t work set up like this, but from what you all have said it is gonna work ? (of course adding a step-up voltage)

i changed the idea of buying a pro mini to an adafruit pro trinket, have you tried this out, or its a bad idea?