Electromagnetic Field Detector #2:
This circuit is sensitive to low frequency
electromagnetic radiation and will detect for
example hidden wiring or the field that encompasses
a transformer. Pickup is by a radial type inductor,
used as a probe which responds well to low frequency
changing magnetic and electric fields. Ordinary
headphones are used to for detection. The field that
surrounds a transformer is heard as a50 or 60Hz
Simple Circuit Creates Magnetic-Card
Lock: 11/08/99 Electronic
Design - Ideas for Design / This is a simple but
interesting circuit to make a magnetic card lock.
Using this lock system, shown in the figure, you can
open a door, switch on a. . .