Mini Screwdriver: Powering Motor and Arduino Nano with 10440 Battery Cells

Hi all,

I'm making the first prototype for a mini electric screwdriver! The objective of this iteration is to establish how to operate the motor I have in mind (Pololu 100:1 Micro Metal Gearmotor HPCB 6V) using a driver (Pololu DRV8838). I'm trying to fit the whole system in a pretty tiny volume, so the most likely candidate for powering the system is two 10440 lithium ion cells in series. For now, I don't want to distract myself with li-ion charging circuits, so this prototype will assume removable, protected cells that I can charge on a dedicated charger. Here is a schematic of what I think might work:

Here are my questions:

  • I am aware that logic and power systems usually like to be isolated from one another. Given that all power is coming from the batteries, I'm not sure what good practice entails. Do I need to do more to this schematic to make sure systems aren't interfering?
  • I have thrown in a Buck converter to bring motor input voltage down. Of course, batteries change voltage over time and the converter would need to be set so that the motor is not over-volted at maximum charge. Is this a good solution? As far as I can tell, a Buck converter does not regulate power to the same output voltage over a range of input voltages. Should I look at a different solution to gain this ability?
  • Are there any other changes you think I should be aware of to prevent sadness and disappointment down the road?

Thanks for your help,

P.S. For some reason inserting images through imgur doesn't work for me. Could I be making a common mistake?


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Ops diag.

Tom... :slight_smile: