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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.

  2. Hello! How do You calibrate the temp sensor? In room tempeature it shows around 70 degrees celsius?

    Also the rotary dimmer is not changing the set value. Have You changed the code lately?

    1. The characteristics of the hotend thermister is defined by this line:

      NTC_Thermistor* thermistor = new NTC_Thermistor(THERMISTOR_PIN, 10000, 100000, 25, 3950);

      "10000" is the 10Kohm resister used in the voltage divider. "100000, 25" means the thermister's resistance is 100Kohm at 25c. 3950 is the "b-value" of the thermister. All these parameters can be found in the datasheet of the particular thermister in your hotend.

      The rotary encoder code hasn't changed. Anyway, the work is mostly done by the "ClickEncoder" library. I am merely using it to read the encoder value. I suggest you isolate the circuit for the rotary encoder and make it work with the "ClickEnoder" library.

    2. Same here, setpoint stays 0, sometimes 5 for a short moment, no matter how I turn the decoder knob. Seems the encoder software library does not run proper on my arduino nano, could be a timer issue, will try another decoder library. Pushing the knob starts the heater which heats up to 40 dgC. Ambient shows 20 so sensor is ok.


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