Open string

OpenString

OpenString is the world's first open-source temperature string for environmental monitoring. It consists of a PCB design, firmware package, and assembly guide to help you bring temperature profile monitoring into any project.

Based on the production temperature string used by SIMB3, OpenString is an extensible, arctic-hardened design that can be used as-is or tailored to your specific application. Everything you need to build, flash, and deploy one is in this repo.

Don't want to build your own? Cryosphere Innovation can supply ready-to-use, assembled OpenString boards. Email cjp@cryosphereinnovation.com for pricing and lead time.

Repository layout

Build your own

1. Read docs/ordering.mdx to order the PCB and parts.
2. Follow docs/open-string-assembly.mdx for the multi-step assembly walkthrough (soldering, housing, potting, testing).
3. Flash the firmware (see below, or docs/firmware.mdx).
4. Deploy.

Hardware

The KiCad project and fabrication outputs live in hardware/:

• hardware/board-files/ — KiCad project (schematic, PCB layout, project settings)
• hardware/fabrication/gerbers/ — Gerbers and drill files ready to upload to a PCB house

See docs/ordering.mdx for the current ordering guide (fab house settings, stencil, assembly options, expected cost).

Hardware design files are released under CERN-OHL-S 2.0 (LICENSES/CERN-OHL-S-2.0.txt).

Firmware

Single-file Arduino sketch at firmware/src/open_string.ino. PlatformIO project config at platformio.ini. Target board: Adafruit Feather M0 (SAMD21).

Building with PlatformIO (recommended)

1. Install PlatformIO Core (or the PlatformIO IDE extension for VS Code).

2. From the repo root (the folder containing platformio.ini):

   pio run                  # compile
   pio run --target upload  # flash over USB
   pio device monitor       # open serial console at 115200 baud

   PlatformIO installs the SAMD board support and the OneWire library automatically based on platformio.ini.

   In VS Code, open the repo root as the workspace folder so the PlatformIO extension can find platformio.ini.

Building with the Arduino IDE

1. Install the Arduino IDE (or arduino-cli) and the SAMD board support package.
2. The Arduino IDE expects the sketch folder name to match the .ino filename — rename firmware/src/ to firmware/open_string/ (or symlink it) and open open_string.ino from there.
3. Select Adafruit Feather M0 as the board, pick the right port, and click Upload.

See docs/firmware.mdx for the full flashing guide, including fuse settings and troubleshooting.

Firmware source is released under GPL-3.0 (LICENSES/GPL-3.0.txt).

License

OpenString is multi-licensed. See LICENSE for the full map. Summary:

• Hardware — CERN-OHL-S 2.0
• Firmware — GPL-3.0
• Documentation — CC-BY-SA-4.0

All three allow commercial use and require attribution. Derivative works must remain open under the same license.

How the docs are published

The OpenString documentation lives at cryosphereinnovation.com/docs. The live site bakes the MDX files in docs/ into its build output when it deploys, so changes here go live the next time the docs site rebuilds.

docs/manifest.json is generated automatically by a GitHub Action (.github/workflows/manifest.yml) on every push that touches an MDX file. You don't need to edit it by hand — just add/edit .mdx files and push.

Contributing

Issues and pull requests welcome. By contributing, you agree to license your contribution under the license that applies to the directory you are contributing to (see LICENSE).

Maintainer and contact

OpenString is maintained by Cryosphere Innovation (a wholly owned subsidiary of JASCO Applied Sciences). Primary contact: Dr. Cameron Planck — cjp@cryosphereinnovation.com.

Contributors are listed in AUTHORS.md.