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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 SDA and SCL pins of the Nano (A4 and A5 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.

  3. Hi All,
    Actually the encoder works without the +5v input, but in this case you'll lose the click function, probably the capacitance and resistive network around the encoder shoud be carefully calculated.
    I solved disconncting the +5 and using an external click button (normally open) in which I feed +5v at one end and A6 and a 1k resistor to ground to the other end. It works.

  4. Hi again,

    I finally finished the electronics and software; I had to customize for a different LCD screen (nokia 5110 I had laying around) and I somehow changed the thermal control routine since I didn't like the way the pid control worked and I did put some other thermal control just in case; anyway If someone wants the code write to at and I'll send it to you.

    1. That's so cool! Mind giving me a brief overview of what you didn't like about the PID control and how you changed it?

      Also, I think it would be best if you could just put your code on GitHub so we can all learn from it.

    2. I had to do it on the fly, but here it is

    3. This comment has been removed by the author.

    4. Also I'd like to send you the schematic with nokia display so you can publish it on your page, if you agree,

    5. Forgot to tell you, the code is named heater_nokia_display.ino under heater-with-display folder.
      What I ddn't like 'bout the pid control?, well it did work, but it was not very stable, I had an histeresys cycle going from +-15 degreec C and sometimes my temps were going much too high almost out of control as if the pid control was very slow to respond, the simple controls I wrote in the code:
      1) check if thermistor cable is disconnected (readings can go negative)
      2) turn off the mosfet if temp is over settemp
      3) put arduino to sleep if there's a thermal runaway

      Obviously these aren't good thermal runaway checks as those you find in marlin code, but they do their job. My heater now stays very stable.

    6. Thanks for sharing! I don't recall having such severe overshot, maybe +5c at most, that's why I let the PWM library took care of everything. But if this approach works well for your setup, maybe others will benefit from it as well.

      As for the schematic diagram, I suggest you create an "images" folder in your GitHub repository and putting the diagram there. Then just link to it in your

      I was new to GitHub when I first started, and learned along the way the "standard" way of doing things. I have always wanted to go back and fix up my old projects as well but kept procrastinating, but I promise I will also fixup my own repository ASAP, and link to your repository.

      Happy New Year!

  5. Hello, I was wondering that to power the thermistor, would 0.5A be enough to heat it up? If not, is 8A overkill?

    Thanks in advance :)

    1. Also, for the MOSFET that i'm using, its rated for 1A to -1A and 80V to 5V. Though, for the power supply that i have, there are outputs of 12V 10A and -12V 0.5A (negative 12 volts 500 milliamps). I am confused why it is in negative volts and was wondering if that would still be usable in this project.

    2. I suspect 0.5A will still do, but it's going to take a much longer time to reach the target temperature. As mentioned in the blog post, I am using a 12V/2A power supply. To be honest, I have never seen a 12V/8A power supply! I would personally be hesitant to use such a large current on such a tiny heater block unless I am really sure about what I am doing!

      Not sure about the -12V/0.5A. Are you sure it's a DC power supply?


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