Picothermal – WebUSB Thermal Camera Using RP2040 and Flir Lepton

Picothermal is a compact USB-C thermal camera built around a Flir Lepton 3.5 sensor and an RP2040 microcontroller, designed to deliver higher-resolution thermal imagery (160×120 pixels) compared with earlier MLX90640-based work. The device offloads display and power to a connected phone or PC, simplifying hardware to an RP2040, USB-C connector, a buck converter (5V→3.3V), a few LDOs and miscellaneous components - no battery, storage or charge controller. The designer chose WebUSB to avoid tying the device to a proprietary app and to make it controllable from browsers (works in Chrome on Android; Firefox lacks WebUSB), while noting that UVC could be added later. Boards were fabricated at Aisler and JLCPCB, with the sturdier Aisler 1.6 mm boards used despite a connector sized for 0.8 mm.

Firmware development initially stalled on TinyUSB but was later completed using agents: a Claude-assisted Rust implementation built on Embassy that uses both RP2040 cores. The firmware works reliably though it’s described as somewhat overengineered and hard to maintain. In retrospect a USB2.0-capable MCU (e.g., STM32) would have been preferable to the RP2040’s USB1.1 limitation. The finished camera connects to a WebUSB landing page on Android Chrome and streams radiometric data; schematics and code are available on Github, with potential future additions like UVC support and extra button functionality.