This is one of those projects that's so obvious in hindsight that I have no idea why I did not set it up years earlier. But let's take a step back ... what is this about?

The Problem

I already blogged about my 3D printing obession in the past and also about the frustration that comes with it from time to time when prints go sideways.

For that reason I upgraded my 3D printer with an attached camera and a WIFI power socket so I can check my prints remotely and even turn off the printer if something has gone wrong.

Note: I'm aware of solutions like OctoPrint for remotely monitoring 3D printers, but my model (a Flashforge Creator Pro) is unfortunately a closed-source device and there's no useful OctoPrint integration. This is why I have to come up with these custom solutions.

But in addition to that, wouldn't it be just nice if my printer could just send me a notification as soon as a print was finished?

Well, it turns out I had all the components in place for that:

• A WIFI socket that reports power consumption.
• A Home Assistant installation.

The Solution

So by simply monitoring the power consumption of my 3D printer, I can tell in which of those states it is:

• Off
• Idle
• Printing

Those states can than be modelled in Home Assistant's configuration.yaml file:

input_select:
  3dprinter_status:
    name: 3D Printer
    options:
      - "Off"
      - "Idle"
      - "Printing"
    initial: "Off"

Then, in automations.yaml I created a few simple rules:

• If power consumption is between 1 and 20 watts and the current state is Off, it goes into the Idle state.

- alias: Set 3D Printer state to Idle when turned on
  trigger:
    - platform: numeric_state
      entity_id: sensor.3d_drucker_current_consumption
      above: 1
    - platform: numeric_state
      entity_id: sensor.3d_drucker_current_consumption
      below: 20
  condition:
    - condition: state
      entity_id: input_select.3dprinter_status
      state: "Off"
  action:
    - service: input_select.select_option
      data:
        entity_id: input_select.3dprinter_status
        option: Idle

• If the printer is Idle and the power consumption falls below 2 watts, this means it is Off again.

- alias: Set 3D Printer state to Off
  trigger:
    - platform: numeric_state
      entity_id: sensor.3d_drucker_current_consumption
      below: 2
  condition:
    - condition: state
      entity_id: input_select.3dprinter_status
      state: Idle
  action:
    - service: input_select.select_option
      data:
        entity_id: input_select.3dprinter_status
        option: "Off"

• If the current state is Idle and power consumption goes above 30 watts, this means Printing has started.

- alias: Set 3D Printer state to printing when power detected
  trigger:
    - platform: numeric_state
      entity_id: sensor.3d_drucker_current_consumption
      above: 30
  condition:
    - condition: state
      entity_id: input_select.3dprinter_status
      state: Idle
  action:
    - service: input_select.select_option
      data:
        entity_id: input_select.3dprinter_status
        option: Printing

• And most importantly, when the current state is Printing and the consumption falls below 30 watts, we know that the print has finished, so the new state is Idle and we can send a notification.

- alias: Set 3D Printer state to Idle when done and send an alert
  trigger:
    - platform: numeric_state
      entity_id: sensor.3d_drucker_current_consumption
      below: 30
      for:
        minutes: 3
  condition:
    - condition: state
      entity_id: input_select.3dprinter_status
      state: Printing
  action:
    - service: input_select.select_option
      data:
        entity_id: input_select.3dprinter_status
        option: Idle
    - service: notify.mobile_app_iphone_von_wolfgang
      data:
        message: "The 3D Printer has finished printing."
        title: "3D Printer"

Works like a charm!