Smart Window

A chain-and-sprocket system drives the window open and closed. The chain runs horizontally along the frame bottom, powered by a NEMA 23 stepper motor on one end with an idler sprocket on the other. Laser-cut finger joints in the acrylic window interface directly with the chain links, converting rotational motion to smooth linear translation.

I initially prototyped a 3D printed gear & rack system, but applying torque at a single corner caused binding; the chain distributes force evenly across the window width. I salvaged the sprockets from a discarded bicycle, both for sustainibility and reliable hardware, then 3D printed a custom adapter to mount the sprocket directly to the motor shaft. Getting proper chain tension proved to be one of the trickier integration challenges; too loose and it would skip teeth, too tight and it wouldn't move. The design scales easily to larger windows by extending the chain and swapping to a larger sprocket.

The system monitors temperature and air quality on both sides of the window. Two temperature sensors and two particulate matter sensors are wired to an Arduino Uno, which decides when to actuate based on configurable thresholds. The control logic uses a 3°F temperature differential threshold with rolling average smoothing across 50 samples to filter sensor noise, and a 20 second reference update to prevent hunting between open and closed states as conditions change gradually. I initially tested with a larger stepper motor but downsized to the NEMA 23 after bench testing showed it provided sufficient torque with lower power draw. I tuned the stepper to run at 2.7A with 800 step microstepping for quiet operation.

I designed a three layer frame construction: an exterior structural layer, a middle spacing layer that houses the chain mechanism, and an interior layer for mounting electronics. I milled half-lap joints into both outer layers for strength; the spacing layer allows the drive system to be assembled independently before final integration.

Acrylic window panes ride on standard drawer slides for low friction travel, while the stepper provides holding power to ensure the window can't be easily forced open. I also tuned the motor torque so it can't overpower a hand caught in the window, which was an important safety consideration for any automated closing mechanism. I housed the electronics in a clear acrylic enclosure to protect from dust while remaining accessible for the purposes of our prototype.

At 20 cycles per day, the window consumes roughly 0.5 kWh annually, which is negligible compared to the ~2,500 kWh a typical residential HVAC draws.

The window responds within seconds to temperature changes; as you can see in the video, body heat via holding the sensor is enough to trigger actuation. With a system of smart windows, residential HVAC could be cut significantly using a night flush cooling strategy, averaging annual savings of 1000+ kWh and $200+. We presented the working prototype at the CU Boulder Engineering Exposition, where it received strong interest from attendees and won the Most Impactful award.