Ultimaker II filament sensor and remote control using Raspberry Pi

The Plan

This is still an idea, growing in my head. I don't know if or when I'll build it.

I want to attach a Raspberry Pi 3 to my Ultimaker II extended.
Obviously with Wifi and USB it will have

• a camera, watching the print
• a GPIO pin an Octoprint API call telling the Ultimaker to pause the print (via a tiny firmware modification)

I will replace the small, plastic filament idler pulley on the back of the maching (opposite to the extruder drive mechanism) and replace it with a ball bearing and 2 sensors

• a trivial 2 bit rotary encoder to meassure the speed and amount of the filament and auto-pause if no filament is transported anymore
• a load cell with a Hx711 module to tell how much pulling force is applied and auto-pause on no force = filament empty and too much force = something blocks the filament from moving

The too much force - part means it will also detect obstacles that would otherwise lead to underextrusion because filament is still being transported but way less then there should be.

• a second load cell in the modified "Low friction UM2 spoolholder" will meassure the weight of the spool and thus tell me how much filament is left.
• the modification is a 12-20cm arm with the load cell attached

Status

1. DONE: Raspberry Pi with Octoprint installed
2. DONE: Designed parts for first prototype (using only Encoder and Dummy-Load Cells)
3. DONE: Rotary Encoder arrived
4. DONE: Pinout specified
5. DONE: Waiting for load cells and Hx711 from China
6. DONE: Test rotary encoder from Raspberry PI command line
7. DONE: Test Octoprint API from Raspberry PI command line
8. DONE:  Convert rotary encoder values to binary positions, movements, direction and speed
9. DONE:  Wrote a simple filament monitor script that detects stalls and reverse movement and pauses the print via the Octoprint API
10. DONE: Test Hx711 and load cell on Raspberry PI using Python
11. DONE: The current "pause" in the Octoprint API is dangerous for scripts. It can resume if issued twice. ->fixed in Octoprint update
12. DONE: solder the final cables and mount things on my UM2extended
13. DONE:  designed modified "608 mount" to weight the remaining filament.
14. DONE:  meassuring the weight of the remaining filament works! 
15. DONE:  Write the final software including monitoring pulling force and spool-scale
16. TODO: Write an assembly instruction including setting up the software.

MKI

MKII

Testing rotary encoder

Testing load cell for extruder pulling force

The software

I'm using a Raspberry Pi running Octoprint as the central controller.
The original plan was to use the Octoprint API.
For the final software (Here on GitHub) I decided to write an OctoPrint plugin.
I can not only detect if filament is supposed to move at the moment and issue a pause command without hacking the firmware and dual-using one of the homing switches as an E-Stop.
I can also display information (such as remaining filament) in the OctoPrint web interface
and offer my meassurements as new values in the OctoPrint API.

The parts

• Low friction UM2 spoolholder - to be modified to pivot on it's hinge in the back of the UM2 and incorporate a load cell
• PEC12R-4225F-S0024 rotary encoder - for filament movement and integrting movement into length used up
• RasPi 3 + OctoPrint bundle 
• set up OctoPrint for UM2 
• Hx711 electrical attachment to RasPi
• C-Code for Hx711 usage on RasPi

New method (using Octoprint API)

• API documentation
• Cura "send to octoprint" plugins 

Old method (using GPIO signal to pause the printer):

• Ultimaker II firmware (for pause via a GPIO pin) 
• Discussion about the same firmware modification I need 
• Nerd firmware with all bells and wistles 
• Open GitHub Issue for filament monitor support 
• Existing Marlin patch to apply for an external pause
• Line, where to apply the patch in UM2Marlin repository