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I am seeking an experienced Automation / Embedded Systems Engineer to develop a robust, custom, production-ready Linux operating system image for a Raspberry Pi 3B+.
The goal of this project is to create a 100% open-source, license-free "Gold Master" image that mimics a Unitronics smart relay/PLC workflow. This image will eventually be cloned across hundreds of offline poultry houses across a large-scale agricultural infrastructure.
🛠️ Hardware Stack (Target Environment)
Controller: Raspberry Pi 3B+ booted completely offline (no internet access).
Shield Stack: Sequent Microsystems Building Automation HAT + Sequent Stackable Smart UPS HAT (communicating via I2C).
Display: Industrial HDMI Touchscreen.
Power: 220V AC input stepped down via DIN-rail Mean Well power supplies (24V DC feeding the UPS HAT, separate line feeding the HDMI monitor).
Outputs: On-board pilot relays triggering heavy-duty 220V AC industrial contactors/SSRs for high-voltage motors, heating, and lighting.
📋 Software & System Requirements
Zero-Licensing Architecture: The entire system must utilize an open-source automation stack. We are using OpenPLC for the IEC 61131-3 visual ladder logic execution engine and Node-RED for the drag-and-drop HMI user interface.
OS Hardening & Kiosk Mode: Built on Raspberry Pi OS Lite. The system must boot directly into a full-screen, fullscreen Chromium --kiosk browser pointing to the local Node-RED dashboard interface. There must be zero access to the underlying Linux terminal or desktop for farm operators.
Display Power Management (DPMS): The system must utilize Linux screen blanking. The touchscreen backlight must completely power down after 5 minutes of inactivity and wake instantly back to the active HMI screen upon a physical touch event.
Hardware Timekeeping (Offline): Synchronize the Linux system clock seamlessly on boot from the Sequent board’s battery-backed DS3231 Hardware RTC chip (hwclock) so the system maintains absolute real-world time accuracy without internet connectivity.
Power Fail Resiliency & Retentive State: The software must listen to the Sequent UPS HAT. Upon 220V main power drop, a script must cleanly save current timer registers to retentive storage, write an event log, and execute a safe Linux shutdown to prevent SD card corruption. On power restoration, it must read the file and resume the cycle state seamlessly.
HMI Password Protection: Implement a supervisor password/PIN keypad screen on the Node-RED interface, preventing unauthorized workers from modifying the timer settings.
Data Logging & Audit Trail: Program local data logging (CSV or SQLite) to the SD card. It must record boot events, power losses, user logins, relay actions (start/stop), and track old vs. new values when configurations are edited. File writes must be buffered to optimize RAM and minimize SD card wear.
Mass Replication Design: The image must be completely abstracted. All local variables (e.g., unique House ID, specific timer intervals) must be read from a local config file. Supervisors must be able to change these local configurations via the password-protected HMI screen so that the exact same master .img can be flashed onto hundreds of identical devices without code changes.
📦 Required Deliverables
A single, universal flashable .img file ready to be duplicated onto standard SD cards.
Clean, well-documented source code files for the OpenPLC logic and Node-RED flows.
A highly clear, visual electrical wiring schematic showing exactly how the Pi, the Sequent HAT stack, the Mean Well power supplies, and the 220V contactors interconnect safely.
