I have a humidity sensor. I would like to measure humidity in some boxes I store the filament in. However, it takes about 10 hours for the humidity to settle after resealing the box, and the battery drain of this particular instrument is pretty high. So I needed a way to switch it on and off inside the box.
A quick hack followed: I removed the button, and soldered a photodiode instead. No extra circuitry was added. It just happens to work.
It's a tool I've been using for ages. A disk from a floppy diskette attached to a motor.
It can cut plastic quite well, yet is completely incapable of damaging metal. This combination of capabilities is super handy in some situations. Examples: stripping a wire; taking connectors apart for repair... and plain cutting plastic =)
In my recent project, I am making a motor with 3d printer. I use plastic to help me wind the coils, then wick the coils in superglue, and cut off the plastic with this tool.
What if you don't have floppy disks to tear apart? Well, actually, you can use other kind of plastic films for making the disk. Transparent sheets for printers work. Even paper will do, although it doesn't last long.
Why does it work?
I believe it cuts by melting the material through friction. It can cut anything that melts easily. PLA, ABS, PVC, POM, polystyrene, and other thermoplastics are all cuttable. Epoxies are not. Polyimide is not.
It can cut rosin. It can also cut solder, but not great (probably because of its high thermal conductivity.
A gentle push on the component with soldering iron - and it sinks into PLA, sticking to it. Larger components can be fixed with superglue (multiturn trimpot, for example). Then I can wire them up with thin wire. And bingo, a small board made out of nothing!
This is a current regulating circuit based on LM317, with fine current adjustment. LED lights up if dropout is above 2.5 V, which is enough for LM317 to regulate properly.