Glasscalibur is a smart opener for horizontal-sliding windows. A NEMA stepper motor drives a lead screw that slides your window open and closed, controlled by an ESP32‑C6 running ESPHome. Control it from any web browser with no app and no cloud account, pair it natively with Home Assistant, or automate it with schedules, sunrise/sunset, or any system that can send an HTTP request (Node‑RED, scripts, IFTTT‑style webhooks, etc.).
The video above has the top cover removed so you can see the mechanism. Under the cover, a custom PCB with an ESP32‑C6 and a TMC2209 stepper driver runs the motor; limit switches at each end of travel give the cover an absolute, self‑correcting position.
- Browser control, no cloud — open
http://glasscalibur-XXXXXX.localon your network and drive the cover, tune the motor, and set schedules. No Home Assistant or account required. - Native Home Assistant — auto‑discovered over the ESPHome API as a real
cover entity (no
command_line/curl glue). - Built‑in scheduling — open/close at fixed times or at sunrise/sunset (with minute offsets), all editable from the browser. Survives reboots.
- Obstruction & stall protection — TMC2209 StallGuard plus an accelerometer‑based vibration‑stall backstop stop the motor when the window jams, is locked, or something gets in the way, and save the position.
- Over‑temperature cutoff — an on‑board temperature sensor stops the motor if it exceeds 80 °C.
- Anti‑tamper alarm — the accelerometer flags if a mounted unit is moved or tilted and sounds a buzzer.
- Over‑the‑air updates — a one‑click Update Firmware button pulls the latest release straight from GitHub. No computer needed.
- Instant manual override — the whole device lifts off the window in a couple of seconds for cleaning or emergencies (see GIF below).
Glasscalibur uses a NEMA 17 stepper motor connected to a lead screw. As the screw turns, a nut travels along it and pushes/pulls the window sash. A custom PCB with an ESP32‑C6‑MINI and a TMC2209 silent stepper driver runs the motor over a single‑wire UART link.
Two limit switches — one at each end of travel — give the cover a known absolute position: every time the carriage hits a limit, the firmware re‑calibrates its step count, so position never drifts. The board also carries:
- a TMP1075 temperature sensor (motor over‑temp cutoff),
- a LIS2DH12 3‑axis accelerometer (vibration‑stall + anti‑tamper),
- a piezo buzzer (tamper alarm), and
- physical buttons (a control button and a Wi‑Fi‑reset button).
The firmware is a single ESPHome configuration — see
firmware/esphome/ for the full, heavily commented config
and a flashing guide.
Safety is the primary concern with this device.
Instant removal. In an emergency the entire device lifts straight off the window — no tools, a couple of seconds.
Obstruction & lock detection. While moving, the cover watches for a stall two ways: the TMC2209's StallGuard reads the motor's mechanical load, and the accelerometer watches for the hard vibration a jammed mechanism produces. If something gets in the way, or the window is locked, the motor stops and saves its position. Both detectors have adjustable sensitivity so you can tune them to your window.
Over‑temperature cutoff. If the motor sensor reads above 80 °C, motion stops automatically.
Anti‑tamper. Once armed, the accelerometer learns the device's resting orientation; if a mounted unit is bumped, tilted, or pried, it raises a Tamper alert and sounds the buzzer.
Before you build or buy, check that the device fits your window. Window sill height is the main factor.
The maximum distance from the top of the window frame to the sill is 2 inches (red text above). More than that and you'll need to raise the opener — a piece of wood such as a 1×4 or 2×4 under the whole device works well.
To attach the window mount (white piece above), you need 14 mm of the lower sash exposed.
The device is just under 22 in end to end, so your window needs to be at least 44 in wide — add 2 in to be safe, so target 46 in.
The motor has been tested up to 40 lb of window. That's very heavy and can cause problems; if your window is that heavy, lubricate the track with dry silicone spray first and see if that helps.
You have several options, and they all work at once:
| Method | How |
|---|---|
| Web browser | Open http://glasscalibur-XXXXXX.local (the XXXXXX MAC suffix is printed on the USB serial log at boot). Full control panel — cover, motor tuning, schedule, diagnostics. |
| Home Assistant | The device is auto‑discovered over the native ESPHome API as a cover entity. No YAML, no curl. |
| HTTP / REST | The ESPHome web server exposes a REST API, e.g. POST http://glasscalibur-XXXXXX.local/cover/glasscalibur/set?position=0.5 (position is 0.0=closed … 1.0=open), and /open, /close, /stop. Drive it from Node‑RED, scripts, or webhooks. |
Two browser‑editable modes, gated by a master Schedule Enabled switch:
- Fixed times — set an Open Time and Close Time.
- Sunrise/sunset — turn on Sun Schedule, set your latitude/longitude,
and optionally an open/close offset in minutes (e.g.
-30to close 30 min before sunset).
Home automation is where this device shines:
- Use an indoor air‑quality sensor (e.g. Awair) to air out a stuffy room.
- Poll PurpleAir hourly and close the window when outdoor air goes bad.
- Compare indoor/outdoor temperature and cool the room when it helps.
- Check a weather API and close the window when rain is forecast.
- Open at sunrise to wake up to the birds.
Full step‑by‑step guides for all of the above live in the project wiki.
| Path | Contents |
|---|---|
firmware/esphome/ |
Current firmware — the ESPHome config (Glasscalibur-esphome.yml) and a flashing/release guide. |
firmware/arduino/ |
Legacy Arduino firmware (the original ESPUI/HTTP build). Kept for reference. |
hardware/v2.0/ |
3D‑printable parts — STEP CAD files plus a ready‑to‑slice print platter (platter-v1.3mf). |
media/ |
Images and GIFs used in the docs. |
To keep it affordable, there's a kit — sourcing the screws and hardware individually gets expensive fast.
Two kit versions are available — one with the 3D‑printed plastics and one without (print your own):
Full assembly instructions and a build video are in the Assembly Guide.
The printable parts are in hardware/v2.0/:
platter-v1.3mf— a ready‑to‑slice PrusaSlicer project with the parts laid out on the bed. Print in PETG at 0.25 mm layer height.- The individual
.stepfiles are the CAD source for each part if you want to modify or re‑orient them.
See the 3D Printing Guide for details.
Installation is fast — a few minutes of work, then a 24‑hour wait for the adhesive to cure.
- Attach the window mount (to the sash).
- Attach the sill mount.
- Wait 24 hours for the adhesives to set, then start using the opener.
Both mounts are adhesive; if needed you can add a screw into the sill, but that hasn't been required. Full details are in the Window Installation Guide.
- First flash of a blank board is over USB with the ESPHome CLI
(
esphome run firmware/esphome/Glasscalibur-esphome.yml) or via web.esphome.io. - After that, update over the air: open the web UI → Diagnostics → Update Firmware (GitHub), and the device pulls the latest release and reflashes itself.
The build, release, and OTA process is documented in
firmware/esphome/README.md.
The project wiki has the full guides:
- 3D Printing
- Assembly
- Window Installation
- Wi‑Fi Setup
- Web UI
- Motor & Stall Tuning
- Scheduling
- Security & Tamper
- API
- Home Assistant
- Firmware Updates
The firmware is licensed under the GNU GPL v3 — see
firmware/LICENSE.
If this project is useful to you, you can support it via GitHub Sponsors.