LED Warning Light Configuration

The LED warning light (three-color signal light) is used to visually display the printer's operating status. This article describes its wiring method and Klipper configuration.

Voltage Specification

LED warning lights come in various input voltage specifications. This article uses the 24V version as an example. Please verify voltage compatibility based on the actual model used.

Wiring Instructions

Cable Color Definition

Color	Function	Wiring Location
Gray	Common Positive	Connect to 24V power positive (e.g., 24V fan power supply)
Red	Red Light Control	Connect to motherboard fan control signal pin
Green	Green Light Control	Connect to motherboard fan control signal pin
Yellow	Yellow Light Control	Connect to motherboard fan control signal pin

Control Polarity

FLY printer motherboards default to negative control:

• The positive (gray wire) of the LED warning light connects to 24V power
• The control wires (red/green/yellow) of the LED warning light connect to motherboard GPIO pins
• When the motherboard outputs a low level, the corresponding color lights up

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Klipper Configuration

[output_pin led_red]
pin: PD12                   # Red light control pin
pwm: False
value: 0                    # Default off
shutdown_value: 1           # Automatically turns on red light when Klipper errors

[output_pin led_green]
pin: PD13                   # Green light control pin
pwm: False
value: 0

[output_pin led_yellow]
pin: PD14                   # Yellow light control pin
pwm: False
value: 0

Pin Description

The example above uses PD12, PD13, and PD14 as example pins. Modify these according to the available GPIO pins on your actual motherboard.

Red Light Failsafe Mechanism

The red light implements a failsafe via shutdown_value: 1:

• Normal Operation: The red light is controlled by macros and remains off under normal conditions.
• Error/Disconnection: When Klipper enters a Shutdown state, the red light is automatically turned on without needing any macro intervention.
• This is a hardware-level safety mechanism. Even if macro logic fails, the red light correctly indicates a fault.

Status Macro

[gcode_macro LED_STATUS]
description: Set LED warning light status
gcode:
    {% set STATUS = params.STATUS|default("idle")|lower %}
    
    # First, turn off all lights
    SET_PIN PIN=led_red VALUE=0
    SET_PIN PIN=led_green VALUE=0
    SET_PIN PIN=led_yellow VALUE=0
    
    # Set lights based on status (active low: VALUE=1 means pin outputs low level, light on)
    {% if STATUS == "printing" %}
        SET_PIN PIN=led_green VALUE=1
        SET_PIN PIN=led_yellow VALUE=1
    {% elif STATUS == "ready" %}
        SET_PIN PIN=led_green VALUE=1
    {% elif STATUS == "warning" %}
        SET_PIN PIN=led_yellow VALUE=1
    {% elif STATUS == "error" %}
        SET_PIN PIN=led_red VALUE=1
    {% endif %}

Status Description

Status Parameter	Lighting Effect	Usage Scenario
printing	Green + Yellow on	Currently printing
ready	Green on	Klipper connected, printer ready
warning	Yellow on	Warning status (e.g., temperature anomaly but no error)
error	Red on	Error occurred, requires attention
idle	All off	Idle status (default)

Call example: LED_STATUS STATUS=printing

Print Macro Integration

Add LED control within print start and end macros for automatic status switching.

Print Start Macro

[gcode_macro PRINT_START]
description: Print start macro
gcode:
    # ... other start logic ...
    
    # Set LED to printing status
    LED_STATUS STATUS=printing
    
    # ... heating, homing, etc. ...

Print End Macro

[gcode_macro PRINT_END]
description: Print end macro
gcode:
    # ... other end logic ...
    
    # Set LED to idle status
    LED_STATUS STATUS=idle

Automatic Status Detection (Optional)

To automatically detect Klipper status without modifying print macros, use the following configuration.

# Status variable macro (for recording the last status to avoid flickering from repeated updates)
[gcode_macro _LED_STATE]
variable_last_status: "unknown"
gcode:
    # This macro only stores variables, no action needed

# Automatic status detection
[delayed_gcode LED_AUTO_UPDATE]
initial_duration: 1
gcode:
    {% set idle = printer.idle_timeout.state|string|upper %}
    {% set printing = printer.print_stats.state|string|upper %}
    {% set current = "unknown" %}
    
    # Determine current status
    {% if printing == "PRINTING" or printing == "PAUSED" %}
        {% set current = "printing" %}
    {% elif idle == "READY" or idle == "IDLE" %}
        {% set current = "ready" %}
    {% endif %}
    
    # Only update LED when status changes to avoid flickering
    {% set last = printer["gcode_macro _LED_STATE"].last_status %}
    {% if current != last %}
        SET_GCODE_VARIABLE MACRO=_LED_STATE VARIABLE=last_status VALUE='"{current}"'
        LED_STATUS STATUS={current}
    {% endif %}
    
    # Continue polling
    UPDATE_DELAYED_GCODE ID=LED_AUTO_UPDATE DURATION=1

Status Determination Logic

Klipper State	Condition	LED Effect
Printing	print_stats.state = printing/paused	Green + Yellow on
Connected	idle_timeout.state = ready/idle	Green on
Error	Klipper enters Shutdown	Red on (handled automatically by shutdown_value)
Other	Status not detected above	All off

Working Principle

1. The _LED_STATE macro stores the last status for comparison.
2. LED_AUTO_UPDATE checks Klipper status every second.
3. It calls LED_STATUS to update lights only when the status changes, preventing flicker.
4. When Klipper errors and enters Shutdown, shutdown_value automatically takes over the red light.