Preventing a roller shade from freewheeling downwards; using the motor a a powered brake

[Jannik698]

I have two roller shades powered by a geared DC motor controlled with a NodeMCU flashed with Tasmota and a LM339 Motor Controller IC. Due to additional circuitry on the PCB the control interface between the NodeMCU and LM339 consists of direction and enable Signals with no possibility of shorting the motor windings.

The problem that im having is, that the motor continues turning after lowering the shades after being turned of because of inertia and low friction inside motor, gearbox and the 3D printed "friction bearing" on the other side of the shade. I have a design in mind where the friction in this "friction bearing" can be adjusted with a screw but initial tests where not as successful as i hoped. Commercial Shades often have a mechanism to only transfer torque from the motor to the shade and not vice versa, similar to higher quality screwdrivers but copying that mechanism seems tricky.

I'm therefore hope to configure Tasmota in a way that drives the motor at e.g. 20% Power when the motor is called to "stop", enough to bring the motion to a secure hold but not enough to roll the shade back up.

I have searched for shutter commands that enable this behavior but were unsuccessful. Does anybody have ideas?