Add plasma cutter relay configuration for GPIO 48 (AUX1)

[Copilot]

Enables plasma cutter control via Solid State Relay on Maslow 4's AUX1 port (GPIO 48) using FluidNC's existing Relay spindle.

Changes

Documentation (docs/PlasmaCutterRelayConfig.md)

• Pin polarity configuration (:low vs :high) and boot safety implications
• ESP32-S3 GPIO boot state behavior - defaults to LOW, making :low polarity safest
• Hardware setup, testing procedure, troubleshooting, and G-code usage (M3/M5)

Configuration Examples

• firmware/example_configs/maslow_plasma_cutter.yaml - Complete working config
• firmware/FluidNC/data/maslow.yaml - Commented template for easy enablement

Configuration

Recommended (relay OFF during boot):

Relay:
  output_pin: gpio.48:low
  off_on_alarm: true

Active-low SSRs (use only if required):

Relay:
  output_pin: gpio.48:high
  off_on_alarm: true

Boot Safety

GPIO 48 defaults to LOW on ESP32-S3 boot. Using :low polarity ensures relay stays OFF until firmware initializes, preventing unexpected plasma activation. Using :high may briefly trigger relay during boot sequence.

G-code: M3 = ON, M5 = OFF

Original prompt

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This section details on the original issue you should resolve

<issue_title>Feature Request: Plasma Cutter Relay Config on AUX1</issue_title>
<issue_description>Goal: I want to configure my Maslow 4 to control a plasma cutter using a Solid State Relay (SSR) connected to the AUX1 port.

Hardware Setup:

Board: Maslow 4 (ESP32-S3).

Port: AUX1 (which I understand is GPIO 48).

Actuator: A Solid State Relay (SSR) controlling the plasma torch trigger.

Current State: I have a PWM-to-10V converter, but I want to omit it and drive the SSR directly using the board's 3.3V logic for simple On/Off control.

Request for the AI:

Please generate the specific maslow.yaml (FluidNC) configuration changes needed to define a Relay Spindle.

Assign the output pin to GPIO 48 (AUX1).

Ensure the configuration uses standard M3 (On) and M5 (Off) commands.

Please verify if there are any specific "Active Low" or "Active High" settings I should check to ensure the relay doesn't trigger unexpectedly during boot.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Feature Request: Plasma Cutter Relay Config on AUX1 #660

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