OpenAR 2.1

OpenAR 2.1 is a DIY thermal augmented reality headset that demonstrates how the OpenAR 2.0 platform can be adapted to new applications. By replacing the microcontroller, modifying some of the 3D-printed parts, and adding a thermal imaging sensor, the headset overlays a live infrared image onto the user’s field of view. Instead of only seeing visible light, you can use OpenAR 2.1 to explore the world through thermal imaging.

OpenAR 2.1, nicknamed “Thermal”, utilizes an infrared camera.

See the invisible

OpenAR 2.1 enhances the user’s vision by detecting infrared radiation. A live video feed of heat sources is reflected toward the user’s eyes, effectively broadening the electromagnetic spectrum visible to humans. Infrared radiation cannot be seen with human eyes, but it can be felt as heat. This is why many infrared cameras are often called thermal cameras.

A view through the headset, captured with a phone from a short distance. The actual user experience is much more immersive!

The headset utilizes an MLX90640 thermal imaging sensor, which measures incident infrared radiation. The radiation may be emitted or reflected by the object. While the sensor does not distinguish between the two, with most materials it can detect the surface temperature of nearby objects with an accuracy of ±1.5 °C.

With thermal imaging, you may be able to “see through” materials that conduct heat. In the left image, you can see the palm and individual fingers that are hidden under the carton in the right image.

How it works

OpenAR 2.1 has the same optics and overall design as the OpenAR 2.0 version. Most of the changes concern the electronics required to run the live thermal camera feed. This also entails modifications to the 3D-printed parts of the headset.

OpenAR 2.1 closely resembles its predecessor.

The thermal sensor captures infrared radiation and sends the data to the development board. The resulting thermal image is then displayed on a small display and directed toward the eyes using a lens, a mirror, and two partially reflective glass plates—one for each eye.

Top-down view of the optical path from the display to the user’s eyes. The light from a single pixel propagates as a diverging cone and is collimated by the lens, which it passes twice due to the mirror. The parallel beams are reflected toward the eyes by the glass plates. The eye closer to the lens sees a brighter image.

The provided software (written in C++) allows you to change the minimum and maximum temperatures drawn onto the LCD display. For example, sunlight coming in through the windows warms the air in the room, which may show in the image as a spotted background. Changing the minimum value to be above these variations cleans up the image.

Components

Below you will find the specific components we used to build the thermal headset. Note—they are only examples. Many of them, if not all, can easily be replaced. The links will take you to retailers where you can order the components or check their technical details. The listed prices vary depending on the supplier. However, the headset can typically be built for about 130 €.

  • Display: 1.3-inch 240×240 LCD display (6–12 €)
  • Glass plates: Cut from a thin sheet of clear glass (2 €)
  • Lens: Cut from +3.5 diopter reading glasses (3 €)
  • Mirror: Cut from a makeup mirror (2 €)
  • Development board: ESP32 FeatherS3 (17-30 €)
  • Thermal camera: Grove Thermal Imaging Camera MLX90640 (70 €)
  • Battery: Rechargeable 3.7 V, 1500 mAh LiPo battery with an integrated protection circuit module (6 €)
  • Accessories: Switch, wires, bolts, filament, heat-shrink tubing… (~10 €)

Downloads

All 3D models, STEP and F3D files, as well as the thermal camera software for OpenAR 2.1 can be downloaded below. The OpenAR 2.1 documentation provides step-by-step instructions for programming the ESP32 FeatherS3 and running the demo. It also includes a circuit diagram for the electronic components.

Note that the optics and headset are almost identical to OpenAR 2.0. For this reason, the documentation only contains what is new in OpenAR 2.1; the full assembly instructions can be found in the OpenAR 2.0 documentation. The original CAD models and print files are also freely available, as well as the demonstration firmware.

Click the following links to download the files.

Licenses

3D models: OpenAR © 2025 by University of Eastern Finland is licensed under CC BY-NC 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/4.0/

Demo program: Copyright 2025 University of Eastern Finland. Licensed under the Apache License, Version 2.1 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at https://www.apache.org/licenses/LICENSE-2.1. Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.