If you don't know what a 3D pen is, well it's a pen that extrudes heated plastic from its nozzle. When Everett Bradford received the 3Doodler 3D pen, he decided to modify its design by not only changing the speed of the extruder but the power input to USB-C as well.
To start, he downsized the filament from 3mm to 1.75mm but did not stop there. He went on to add sections of tubing to center the filament before it reaches the extruder. After this, with high-precision on the hardware, Bradford could control the speed to achieve the rotation measurement periods in the range of 50-200ms.
"The cooling fan upgrade was much simpler, I just installed a thermistor on the cold end of the extruder to monitor its temperature," Bradford explains. "This is an 0603-thermistor wrapped with kapton and mounted to the cold end with CA glue."
Finally, after accessing the control board of the 3D pen, it came with an unlabelled 16-pin SOIC part. So the first thing was to replace it with the PIC16F1579 in a QFN package using 34AWG enameled magnet wire.
With all this, the hardware enhancements were complete, but it was time to work on the firmware. If you are interested in custom firmware, the source code is available on GitHub. But there was more to the hacking of the 3Doodler 3D pen. The final upgrade involved changing the power input to 5V USB-C, which enables the device to run from a power bank.
Those interested in Bradford's 3Doodler hack can find more details in his blog post.