Data Sheet

Project 67
Reed Switch with Electromagnet
Build the circuit as shown, and turn on the slide switch (S1). The electromagnet (M3)
should be activating the reed switch (S9), which turns on the white LED (D6). Raise
the iron core rod in the electromagnet (or remove the rod) to turn off the LED.
You can also remove the electromagnet and instead connect it to the circuit using the
red & black jumper wires, then hold it near the reed switch to turn on the LED.
Project 68
Build-Your-Own Reed Switch
Build the circuit as shown. There are three 2-snap wires at base grid locations
A1-B1. Snap the 6-snap wire at base grid location F5, then place it so it lays
on the snap at grid location B2 (DO NOT SNAP IT ON). A 3-snap wire is
placed across grid locations B1-B3, with the left side on lever 4 and the right
side on level 3; sure it is securely snapped. Place the nut snap on the 6-snap
wire.
Turn on the slide switch (S1); the top lamp (L4) lights.
Now hold the magnet just above the nut snap to attract it; this should turn off
the top lamp. Use the magnet to raise the 6-snap wire until its loose end con-
tacts the bottom of the 3-snap wire, which should turn on the bottom lamp.
Moving the magnet up and down above the nut snap should attract and re-
lease it, raising and lowering the 6-snap wire, flipping the lamps on and off.
Reed switches are used as proximity switches and in door and window
sensors for burglar alarms. Speed sensors on bicycles use a reed switch
to detect when a magnet on the wheel passes the sensor.
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