A custom thermal camera called Picothermal sends live infrared images to a phone or computer over USB-C, then lets a Chrome-based browser operate it through WebUSB. It is not a conventional webcam: an RP2040 microcontroller speaks directly to a FLIR Lepton 3.5 thermal core, while JavaScript in the browser handles the device protocol. The result is a camera that needs no separately maintained companion app, but does require a compatible Chromium browser and custom firmware.
What the WebUSB thermal camera is
Adafruit’s October 13, 2026 report describes builder Cezar Chirila’s Picothermal project. The design replaces an earlier 32×24-pixel MLX90640 sensor with a FLIR Lepton 3.5, reported at 160×120 pixels. The camera connects through USB-C to a host phone or computer; that host supplies the browser interface and display.
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Hackaday’s October 15, 2026 coverage describes the same architecture: the Lepton sensor is connected to an RP2040, and a browser landing page starts the camera. This is a custom embedded instrument rather than an off-the-shelf USB webcam.
How WebUSB operates the camera
WebUSB is a browser API for non-standard USB hardware. Chrome’s documentation says its purpose is to make USB safer and easier to use from the web. After the camera is plugged in, a page calls the WebUSB device chooser; the user selects the camera and grants access. Browser JavaScript can then open the USB connection, exchange the project’s commands and image data, and render the thermal view.
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That approach moves the device protocol into the web page instead of a native desktop or mobile application. Chirila’s stated reason for choosing WebUSB was that the camera could work from a browser page “with no app to maintain.” Hackaday summarizes the user experience as visiting a landing page in a browser that supports WebUSB and using the camera.
Browser support
Use Chrome or another Chromium-based browser with WebUSB enabled. The Adafruit report specifically notes that Firefox does not support WebUSB, so a Firefox-only workflow will not connect to this project. A browser chooser permission is still required; simply plugging in the cable does not automatically give a page access to the device.
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Hardware inside the design
| Part | Role and reported details |
|---|---|
| Thermal core | FLIR Lepton 3.5, reported as a 160×120 infrared array in the project coverage. |
| Microcontroller | RP2040, handling the sensor interface, USB descriptors and device protocol. |
| Host connector | USB-C; the connected phone or computer provides the browser, display and USB host connection. |
| Voltage regulation | A buck converter steps 5 V to 3.3 V, with several LDO regulators for the required rails. |
| Built-in accessories | No integrated battery, charger, screen or microSD card is described. |
The Lepton family is an LWIR OEM camera-module line with 80×60 and 160×120 variants, multiple field-of-view choices and radiometric-capable models. Teledyne FLIR’s product information distinguishes those options, so “Lepton” alone does not identify one resolution, lens or temperature-measurement capability.
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- Use compatible hardware. Assemble the RP2040, Lepton core, USB-C connection and regulated power circuitry, or obtain a completed build that exposes the project’s USB interface.
- Connect the cable. Plug the camera into a phone or computer with USB host support. Because the design has no internal battery, the USB connection is also the camera’s power path.
- Open a Chromium browser. Use Chrome or another browser based on Chromium with WebUSB support. Do not expect Firefox to provide the required API for this project.
- Visit the project landing page. The page contains the browser-side JavaScript that knows how to communicate with the RP2040 device.
- Choose the camera in the USB dialog. Approve the browser permission when the device chooser appears. WebUSB access is permission-gated rather than automatic.
- Start the stream. Once the page opens the USB interface, its code requests thermal frames and draws them on screen. Disconnecting the cable, denying permission or using an unsupported browser prevents this step.
What you must build or integrate
Sensor and breakout hardware
The natural starting point is a FLIR Lepton thermal camera module. A FLIR Lepton breakout board can simplify the mechanical, power and signal connections during prototyping, but it does not by itself turn the sensor into a WebUSB camera. The RP2040 firmware, USB descriptors and browser protocol remain necessary.
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Firmware and USB protocol
The microcontroller must initialize the Lepton, package frames and expose a USB interface that the page understands. This is the principal engineering difference from a UVC camera: the device is not presenting a standard webcam stream that operating systems already know how to open. The browser code and firmware must agree on endpoints, commands, framing and data format.
Power design
The reported build converts 5 V USB power to 3.3 V and uses additional LDO regulators. A Lepton design therefore needs a correctly sequenced, adequately regulated supply; USB-C provides the connection, but it does not remove the need to design the power rails. There is no stated battery-life figure because the reported hardware has no built-in battery.
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WebUSB versus a conventional UVC thermal camera
| Consideration | WebUSB Picothermal design | UVC thermal camera or phone accessory |
|---|---|---|
| Browser operation | Requires Chrome or compatible Chromium WebUSB support and a permission grant. | Usually appears as a standard camera, or relies on the accessory maker’s supported app. |
| Native app or driver | Project goal is no separately maintained app; browser JavaScript carries the protocol. | May use operating-system camera support, a driver or a vendor app. |
| Reported sensor resolution | 160×120 with the Lepton 3.5 used in the project. | Varies by product and sensor. |
| Radiometric temperature data | Not established by the project reports; it depends on the chosen Lepton model and firmware. | Varies; a visible heat image does not automatically mean calibrated temperature measurement. |
| Field of view | Depends on the selected Lepton lens configuration. | Depends on the product’s optics. |
| USB complexity | Requires custom descriptors, firmware and browser-side protocol code. | Standard UVC handling can reduce host-side integration work. |
| Open implementation | Designed around a custom RP2040-and-browser stack. | Often depends on the manufacturer’s software and documentation. |
| Total build cost | Not stated; includes the Lepton module, controller, regulators, PCB or breakout and assembly. | Varies by accessory and software bundle. |
Which Lepton module should you choose?
Choose by resolution, lens and measurement requirements rather than by the family name alone.
- Resolution: the project’s Lepton 3.5 is reported at 160×120. Teledyne FLIR also lists 80×60 Lepton variants.
- Field of view: select the lens that matches your working distance and scene coverage; the family includes multiple options.
- Radiometry: if you need numerical temperature readings, verify that the exact module is radiometric-capable and that the firmware preserves the required data. The project reports do not establish measurement accuracy.
- Integration: confirm the breakout’s voltage requirements, connectors and mechanical fit before designing the RP2040 board.
- Availability: listings and stock for a Lepton 3.5 can change, so verify the exact part and seller before purchase.
Limits and practical failure points
- Unsupported browser: Firefox will not provide the WebUSB path identified for this project. Switch to Chrome or another compatible Chromium browser.
- No chooser entry: check the USB cable, power rails, USB descriptors and whether the firmware is exposing the expected interface.
- Permission denied: reconnect the device and repeat the browser permission flow, selecting the correct USB device.
- Image works but temperatures are unreliable: a 160×120 thermal image is not proof of radiometric accuracy. Confirm the Lepton variant, calibration behavior and data handling separately.
- Phone incompatibility: the phone must support USB host operation and a Chromium browser with WebUSB; the reports do not promise support for every handset.
No independent frame-rate, thermal-accuracy, power-draw or battery-life measurements are established for the reported build. Those figures should be treated as unknown until measured for a particular hardware revision and browser.
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Frequently Asked Questions
Can a FLIR Lepton work over WebUSB?
Yes, in a custom design such as Picothermal: an RP2040 connects to the Lepton, exposes a custom USB interface and a Chromium page exchanges the device protocol. A Lepton module alone is not automatically a WebUSB camera.
Do I need a separate app or driver?
The project is intended to avoid a separately maintained native app by putting the protocol in browser JavaScript. You still need the project firmware, landing page and a browser with WebUSB support.
Does this provide calibrated temperature readings?
Not necessarily. Radiometric capability depends on the exact Lepton model and implementation; the project reports establish the thermal image resolution, not measurement accuracy.
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