Smoothie Kill Button

There are two solutions for implementing a kill button on the Smoothieboard:

LED Tactile Button

Solder an LED Tactile Button on the Smoothieboard.

Led Tactile Button

Simple Button

Wire a simple button on two pins.

Simple Button

The button may be configured as a kill switch, which will halt all operations, turn off heaters, and pause the host. It can be cleared with a M999 command or by resetting the board. To enable a kill button, the following configuration is added:

kill_button_enable                        true             # set to true to enable a kill button
kill_button_pin                           2.12             # kill button pin. default is same as pause button 2.12 (Add ^ for external buttons)

[kill button]
enable = true                # set to true to enable a kill button
pin = 2.12                   # kill button pin (Add ^ for external buttons)

When in the halted state (after the kill button is pressed), the play LED will flash rapidly. The kill state can be cleared by holding down the kill button for 2 seconds or more.

Alternatively, a latching E-Stop button can be hooked up to the kill button header (usually normally open). Then use this config:

kill_button_toggle_enable        true                # allows for latching estop button

[kill button]
toggle_enable = true         # allows for latching estop button

When the E-Stop button is hit and latched on, it will halt the system. When it is unlatched and released, the system will exit the halt condition.

If you do not want the halt to exit when it is released, then set this:

unkill_enable     false                # do not unkill when button held or released

[kill button]
unkill_enable = false        # do not unkill when button held or released
Normally Closed (NC) Kill Button Warning: If your kill button is "Normally Closed" (NC), it will be pressed at boot time. By default, the bootloader reads the 2.12 pin at boot time and if it is closed, will enter DFU mode. This means that you cannot use pin 2.12 for a normally closed kill button as it will prevent the board from booting normally. The solution is very simple: just use any other pin and edit the configuration accordingly.

Stopping Smoothie

There are several different ways to stop Smoothie during operation, each with different behaviors and use cases.

Understanding these methods is important for safe operation and troubleshooting.

Stop Methods Comparison

Command G-code Movement Heaters File playing Recoverable Documentation
abort M26 Stops SDCARD print immediately Not affected Aborts Position maintained, file must be restarted Player
suspend M600 Stops once queue is empty Turned off (if option enabled) Paused, can be resumed Yes, with resume or M601 Player
Kill button M112 Stops instantly (if button), waits for buffer (if host) Turned off Aborted No, position lost, home required supported-g-codes
Control-X - Stops instantly, works during streaming Turned off Aborted No, position lost, home required -

Detailed Method Descriptions

Abort Command (abort / M26)

Stops the execution of a file being played from SDCARD.

Behavior:

  • Completes the current G-code
  • Stops immediately after that
  • Discards the rest of the queued commands
  • Attempts to maintain the correct position after the abort
  • Heaters remain at their current state

Use Case: Quick stop of a print job while preserving position and keeping heaters on.

Recovery: Position is maintained, but the file must be restarted from the beginning.

Documentation: Player module

Suspend Command (suspend / M600)

Suspends the execution of a file being played from SDCARD or being streamed from a host.

Behavior:

  • Stops once the movement queue is empty
  • All state is saved
  • Heaters turned off by default (configurable)
  • Jogging and extruding are allowed during suspension
  • Can be resumed with resume or M601

Use Case: Mid-print filament change or filament out detection.

Host Support: Requires upstream support. Currently Pronterface and OctoPrint support it. Other hosts need to be manually paused.

Recovery: Yes, fully recoverable with position maintained.

Documentation: Player module

Kill Button / M112

Emergency stop that instantly halts all operations.

Behavior:

  • If kill button pressed: Stops instantly
  • If M112 issued from host: Has to wait for the receive buffer to have room
  • All heaters turned off
  • File playing aborted
  • Position is lost
  • System enters Halt state until M999 is sent

Use Case: Emergency situations requiring immediate stop.

Recovery: No, position is lost. Homing will be required.

Documentation: Supported G-codes, Kill Button

Warning: Using the kill button or M112 will cause position loss. You must home all axes before continuing normal operation.

Control-X

Sends a control character to stop Smoothie instantly.

Behavior:

  • Works at any time, even when streaming
  • Same effect as the kill button
  • All heaters turned off
  • File playing aborted
  • Position is lost
  • System enters Halt state until M999 or $X is sent

Use Case: Emergency stop from terminal/console when streaming G-code.

Recovery: No, position is lost. Homing will be required.

Halt State

When the kill button is pressed (or there is a temperature fault, M112 is issued, a limit switch is hit, or other error), the system enters the Halt state.

Halt State Behavior

Halt State Indicators:
  • Play LED flashes
  • Any command issued from host gets a !! response (with a few exceptions)
  • PSU may be turned off if a PSU Switch is defined

Clearing Halt State

The Halt state can be cleared by:

  1. Issuing M999 from the host
  2. Holding the flashing kill button for 2 seconds
  3. Using the LCD panel (if equipped)

Using Buttons and Sensors

Tip: All stop commands can be triggered by a button or a sensor if a Switch module is configured to do so. This allows for physical emergency stop buttons or automatic stopping based on sensor conditions.

Best Practices

For Normal Operation

  • Use suspend/resume (M600/M601) for planned interruptions like filament changes
  • Use abort when you need to stop quickly but keep heaters on

For Emergencies

  • Use the kill button or Control-X for immediate emergency stops
  • Remember that position will be lost and homing will be required

Recovery After Emergency Stop

  1. Clear the Halt state with M999
  2. Home all axes before attempting further movement
  3. Check that heaters are at safe temperatures before proceeding
  4. Verify machine state before resuming work

Further Reading

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