Button cells for arduino uno

Question

OK, before I start I know that there is significant difference and that the Arduino Uno is not designed to run off button cell batteries especially to run both the board AND its load but what if the load is on a different power source?

I need to run 2 micro servos to operate a type of elevator styled door system. One Uno sketch I came across mentions that the 2 opposite running bi-directional motors need to be on a separate power source than the Uno itself. My goal is to run my apparatus with as few batteries (must be batteries preferably 1 9V and 2 CR2032) as possible to maintain design.

Now, since the servos obviously would kill the button cells in no time I was thinking i might be able to power the microcontrollers off the BCs and the servos off the 9V. This is not a continuous action device as I stated the doors close and the system stops until the same button or a separate one is pressed then they reopen and stay.

Anybody feel that this might be possible or should I resort to a 6V camera battery. A key factor is that this is a sort of prototype for a toy and thus I am trying to make it as practical as I can.

Even the servos and Uno are a far step to me but with the limited space I am working with I am having trouble finding simpler mechanical options with significant power.

• jippie: Arduino is designed to run its own peripherals from the on board regulators. There is very limited room designed in for the load.

Answer 1

Determine the current necessary to run the servos from their datasheets. Then make sure they can handle the higher voltage. Then make sure the 9v cell has the capacity to run it as long as you want it to (broad estimates will do). A 9V will likely have between 400mah and 600mah. That's milli-amps times hours if you didn't know. So for instance, if the servo draws 0.5 amps at 9V then it could run (be actively on) for about 1 full hour before crapping out.

As long as you know how to drive the Uno separately from the load then yes, this idea should work fine. You'll need either relays, bjt's or mosfets to take the signal from the Uno and drive the servo in this manner. I'd recommend N-MOS's to do that job.

Lastly, more details in your question would result in more details in answers.

Answer 2

Coin cell batteries are low capacity, low draw. Designed for long term use at < 10mA. A cr2302 has about 250mAh. A ATMega328 like the uno has, fully on, with no outputs driving any current device (like leds), will have 25~50mA draw, or more. In sleep modes, this can be a lot less. Arduino doesn't really deal with sleep modes, so you have fully on microcontroller, plus leds and peripherals. You will drain a cr2302 in no time flat.

Without using sleep modes and depowering the arduino leds and the ft232 or usb atmega that does the serial to usb, the draw is too great for anything other than a 2 3 hours tops.

A bare bones arduino, essentially just a atmega328 or attiny, taking advantage of sleep modes, is better.