Make: Volume 91

thin metal leaves that bend and touch each other

when a magnetic field is very close.

I found that the sensor had to be within 1 inch

of a 10cm neodymium magnet to detect it. There

is no sensitivity adjustment, the leaves of the

switch are either touching or they aren’t. A small

LED on the end of the gooseneck lights when a

field is detected. As an extremely scientific test to

verify that the sensor is a reed switch, I whacked

the end of the gooseneck soundly (on the theory

that a brief mechanical insult would bounce the

leaves of the switch together) and saw a brief

flash of the LED.

DETECTING RETROREFLECTION

A retroreflector is a device that ...