Elenco Snaptricity® - Manual (Page 77)

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Reed Switch Project #67
Build the circuit as shown. Place paper clips at base grid
locations B1 and B3, beneath all the parts (this is used to
raise the parts slightly). Snap the 6-snap at F5, then place
it so it lays on the snap at B2 (DO NOT SNAP IT ON).
Place the nut-snap on the 6-snap.
Assembly
Set the slide switch (S5) to position C to turn on the circuit,
lamp A (L4) should be on.
Now hold the magnet about 0.1 inch above the nut-snap to
attract it, this should turn off lamp A and turn on lamp B.
Moving the magnet up and down slightly above the nut-snap
should attract and release it, flipping the lamps on and off.
Operation
Description
This circuit acts as a reed switch , which is an electrical
switch operated by a magnetic field. In this case, the magnet
uses the reed switch to control the lamps.
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.
Educational Corner:
An actual normal open reed switch has two metal
tabs inside a glass tube. A magnetic field brings
the tabs together to complete a circuit. Here is a
typical reed switch:
Electric
Paths
Glass Seal Glass Tube
Thick Wire Contacts
W. B. Elwood invented the reed switch at
Bell Telephone Laboratories in 1936.
N
S
Paperclips