Filament Joiner Part 2 (With Display and Knob)

Thanks to the current corona-virus crisis, the parts I ordered for the filament joiner project were taking forever to arrive. But now that they have finally arrived, I can put them to good use.

These were the parts ordered:
Here is the final circuit diagram:
The OLED display is connected to the SCK and SDA pins of the Nano (A2 and A3 respectively), and powered by 5V and GND.

The rotary switch encoder is connected as follows:
  • VCC => 5V
  • GND = > GND
  • CLK => D9
  • DT => D8
  • SW => D2
My prototype board now looks like this:

The updated code for driving the knob and display is available in heater-with-display.ino in the Github repository.

We now have a fairly compact (about 7cm x 5cm) and independent filament joiner (no need to connect to PC) that is driven solely by a 12V power supply.

Here's how to use it to join printer filaments.

More usage details in my previous post.


  1. If you already utilize a hot end, why would you not actually run the filament through a nozzle instead of grinding the filament against the outside edge of the block?

    The hot end was specifically designed to do exactly what you're trying to do - heat filament to a desired temp. Now that you've figured out the hard part, it seems pretty straightforward to add a nozzle, maybe add a chamfer to the "exit" side for easier insertion of the 2nd piece of filament, and tune the temps appropriately.

    1. You don't actually need to add a nozzle. One of the things I have tried initially is to drill a 1.75mm hole through the hotend, align both ends of the filament through the hole, then heat the hotend up to 180c. I quickly learnt that once the filament starts melting, things turn gooey very quickly and the filaments will fall off the hole, even if I quickly turn power off the hotend. Lesson learnt is that once the filament starts melting, it turns into a liquid mess and you lose control over it very quickly.


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