Firmware

The OpenString firmware is a single Arduino sketch that reads the DS28EA00 sensors in sequence and prints each reading over serial in physical cable order. It's designed as a starting point you can adapt into your own sketch or firmware.

The source lives in firmware/src/open_string.ino. It's heavily commented; if you're porting to another platform, the inline notes are the canonical reference.

What the Sketch Does

On boot, the sketch walks the chain in chain mode, which allows the firmware to discover each chip's 64-bit ROM address in physical cable order. Once discovered, the main loop kicks off a Convert T on every chip simultaneously, then reads each scratchpad in order and prints the temperature.

Hardware Requirements

OpenString needs three things from the host microcontroller:

• A 3.3 V GPIO for the 1-Wire data line
• A 3.3 V supply and shared ground
• A 4.7 kΩ pull-up resistor between the data line and 3.3 V

The 1-Wire protocol supports parasitic power, but we don't recommend it for OpenString — 20+ chips drawing simultaneously during Convert T produces inconsistent results. Use a dedicated 3.3 V supply from your board or external power supply.

The sketch is verified on an Adafruit Feather M0 but should run on any Arduino-compatible board with a free GPIO.

Setup

The firmware is set up as a PlatformIO project (platformio.ini in the repo root), but the sketch also runs directly in the Arduino IDE if you prefer. Either path needs the same single dependency: the OneWire library.

Option A: PlatformIO (recommended)

1. Install PlatformIO — the VS Code extension is the easiest path.
2. Clone the repository and open the open-string folder.
3. Build and upload:

pio run -t upload

pio run -t upload

PlatformIO reads platformio.ini, installs OneWire automatically, and flashes the configured board (default: adafruit_feather_m0). To target a different board, edit the [env:...] block in platformio.ini — see PlatformIO's board list for IDs.

Option B: Arduino IDE

1. Install the Arduino IDE (2.x recommended).
2. Install the board support package for your target (e.g. Arduino SAMD Boards for the Feather M0).
3. Install the OneWire library via Sketch → Include Library → Manage Libraries….
4. Open firmware/src/open_string.ino, select your board and port, and click Upload.

Configuration

The tunable constants live at the top of open_string.ino:

For most uses, only DATA_PIN and INTERVAL_MS need touching.

Expected Output

After flashing, open the serial monitor at 115200 baud. You should see something like:

=== OpenString firmware ===
Data pin: D2

Discovered 20 sensor(s) in physical cable order:
  1: [42 11 22 33 44 55 66 AB]
  2: [42 11 22 33 44 55 66 CD]
  ...

--- t=823 ms ---
  1: 18.31 C
  2: 18.00 C
  3: 17.75 C
  ...

If discovery returns 0 sensors, check the pull-up resistor and the harness wiring (red→VDD, black→GND, white→data).

Porting to Other Platforms

The sketch is structured so the chain-mode discovery and per-chip read sequences map cleanly to any 1-Wire master. If you're moving to ESP-IDF, MicroPython, Zephyr, or a bare-metal driver, the byte sequences (CHAIN ON, CONDITIONAL READ ROM, CHAIN DONE, Convert T, Match ROM, Read Scratchpad) are the same — only the surrounding I/O changes. The inline comments in open_string.ino walk through the protocol step by step.