Ultra simple, cheap, extremely sensitive DIY seismometer

Ran across this exciting new idea today, with great hands-on educational possibilities for young science students: Extremely Sensitive Cheap Homemade Seismometer - Arduino Project Hub

A couple of years ago I built the TC1 seismometer, which works very well, but it is technically difficult for young students to make the detector, especially winding the coil. Most schools that undertake the TC1 project buy the kit, which is pretty expensive.