I made an automatic roller blind from a spare NEMA17 stepper that was laying around, I didn't want to buy a new one with planetary reduction neither another DC motor, so here it is.

My original blinds used a tube with 29mm external and 28mm internal diameter.
It's needed just 2 screws to secure the tube holders to the wall supports (almost as a shaft but it will just hold everything in place, they must spin freely) and a grub allen M3 to hold the motor's pinion in place.

The electronics I used were a NEMA17 stepper, a NodeMCU, a stepper driver (initially an A4988, then a TMC2208), a step down and a 12V power supply. I put everything together in a simple prototyping PCB for now.
I'm using the Tasmota firmware, very well documented here: https://tasmota.github.io/docs/Blinds-and-Shutters/
This could vary a lot, depends how you want to control the motor.

The 1st version was just a reduction gear, going straight to the blind's tube, very fast but didn't have a brake, so the blinds felt as soon the stepper was powered off.
The 2nd, I adapted the original blinds cord's system that has a spring that acts as a brake, cool design but with a play that could not be compensated without a closed loop system.
This version n. 3 is slower but uses a worm gear that naturally locks the movement, very precise and has no play.

It is VERY important to play attention to tolerances in the motor shaft's hole, remember the pinion will withstand the weight of the whole blind, it needs to be tight and secure. The Support - Motor Side.stl has a dent that will hold the pinion from pop out but it still could spin freely if the shaft's screw doesn't have a flat side to sit.

I attached the .step and fusion files to make it easier to adapt.

The critical part to print is the worm gear, I used PETG and 0.12mm/layer, with the hole facing up and the "spiral", down. I don't see any problem to use PLA at 0.28mm/layer for everything else, maybe the Tube Holder - Motor Side.stl would be better at 0.12-0.20mm/layer due to the gear, but it will work anyway.

Print details:

• No support needed
• Worm gear: Use 999 walls
• Supports: use at least 50% of infill and 4 walls
• 20% infill for the rest are plenty.