Machine Access Interlock Controller

Overview

The Machine Access Interlock Controller is an industrial safety device intended to be used in conjunction with the site access control system to ensure a machine can only be enabled (powered) when all safety interlocks are engaged (“sealed”), and the user is authorised. It disables the machine if any interlock is broken or a fault is detected. Upon enabling the machine, timers ensure the machine does not remain enabled once the user has finished. Machine run-time is detected via current transformer input, with configurable threshold, calibration, and amps-per-volt ratio. Designed for reliability and configurability, with persistent configuration stored in flash memory, and provides a serial terminal menu for setup and diagnostics.

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Features

• Multiple Interlock Inputs: Four independent interlock channels, each can be enabled/disabled in software.
• Safety Relays: Controls contactors and output gates to enable/disable machine power.
• Current Sensing: Monitors machine current via CT (current transformer) input, with configurable threshold, calibration, and amps-per-volt ratio.
• Timers: Configurable enable (pre-start) and pause (post-stop) timers.
• Fault Detection: Detects faults such as power supply undervoltage/overvoltage, CT disconnect, overcurrent, and running while disabled.
• Status Indication: RGB LEDs for status, enable, and interlock indication.
• Persistent Configuration: All settings are stored in flash memory and survive power cycles.
• Serial Terminal Menu: Interactive configuration and status via serial terminal (115200 baud), with ANSI color support.

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Hardware Overview

• Inputs:
  • 4× Interlock inputs (dry contact, pulled up)
  • 1× Enable input (dry contact, pulled up)
  • 1× CT analog input (current transformer)
  • 1× PSU voltage feedback
• Outputs:
  • Contactor 24VDC coil control
  • Machine status (running/idle)
  • Fault/alarm status
  • Status RGB LED
  • Enable and interlock LEDs
• Board: Custom board definition (scion_isc_m0.json), with pin mappings in src/sys_init.h.

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Configuration & Operation

• On power-up, the device loads configuration from flash. If not initialised, it writes defaults.
• The main loop continuously checks interlock status, current draw, and handles timers.
• If all interlocks are sealed and enable input is active, the machine can be enabled.
• If any interlock opens or a fault occurs, the machine is immediately disabled.
• Configuration (interlocks, timers, current settings) is accessible via the serial terminal menu.
• All changes can be saved to flash for persistence.

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Persistent Storage

• Uses a flash_data struct to store:
  • Interlock enable/disable states
  • Enable & pause timer values
  • Current threshold
  • CT calibration multiplier
  • Amps-per-volt ratio
• Data is validated on load; defaults are restored if out-of-range.

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Serial Terminal Menu

• Connect at 115200 baud.
• Menu allows:
  • Enable/disable interlock inputs
  • Setting enable/pause timers
  • Adjusting current threshold
  • Setting CT ratio and calibration
• Changes can be saved to flash by typing 's' in the menu.

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Faults Detected

• Power supply undervoltage/overvoltage
• CT disconnected
• Overcurrent
• Running while disabled (tamper detection)

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Building & Flashing

• Platform: Arduino (via PlatformIO)
• Board: scion_isc_m0 (custom board)
• Build:
  • Install PlatformIO
  • Build and upload using PlatformIO, or use Arduino IDE with proper board support
• Configuration: See platformio.ini for environment and dependencies

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Project Structure

• src/ – Main source code
• hardware/ – Schematics, PCB, and pinout documentation
• boards/ – Custom board definition
• lib/ – Libraries (including FlashStorage for persistent config)
• platformio.ini – PlatformIO build configuration

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License

(C) 2024 Scion Research. For internal and research use. See source files for details.