3D Printer Filament Joiner

After trying out numerous options, this is my solution for joining printer filaments.

It uses an Arduino Nano and a MOSFET for driving a cheap 3D printer hotend to the desired temperature. By melting the filament at the correct temperature, the joint created is very strong and not brittle at all (which is what happens if one uses an uncontrolled heat source like a candle).

Also, the contraption is cheap and should cost less than $15 in total.

I have done some writeup about the circuitry required:
https://www.randseq.org/2020/02/3d-printer-filament-joiner.html

And here, adding an OLED display and rotary knob for a totally independent unit that does not need to be tethered to a PC:
https://www.randseq.org/2020/03/filament-joiner-part-2-with-display-and.html

Video of how the joint is performed:
https://www.youtube.com/watch?v=rC_HjhM3sgA