Automated Light-Responsive Blinds Controller

Commercial motorized window-blind systems typically cost US$150 - 500 per window and require permanent installation, which limits the practical adoption of automated daylighting and solar-gain management in residential settings. This work presents the design, fabrication, and experimental validation of a fully retrofittable mechatronic actuator that engages an existing manual tilt wand through a 3D-printed friction-fit coupler, without modification of the host hardware. The system integrates a cadmium-sulfide photoresistor in a 1 kΩ voltage-divider configuration for ambient-light sensing, an ATmega328P (Arduino UNO R3) microcontroller running a software Schmitt-trigger control law with a 100-count dead band, and a 28BYJ-48 geared unipolar stepper driven through a ULN2003 Darlington-array driver. A closed-form static torque analysis, based on an empirically anchored equivalent-load model, predicts a design margin of 3.2× against the worst-case wand-rotation load. The prototype was exercised over fourteen consecutive day-night cycles. All fourteen open and fourteen closed transitions completed successfully with no missed steps, no false triggers within the calibrated illumination range, and a maximum coupler-housing surface temperature of 31?C. The total bill-of-materials cost is approximately US$37, an order of magnitude below comparable commercial solutions.