Make Electronics

Switching Basics and More 57

Experiment 7: Relay-Driven LEDs

A

B

C

D

D

Figure 2-51. This is one way that the parts inside a relay can be arranged. The coil, A, gener-
ates a magnetic attraction pulling lever B downward. A plastic extension, C, pushes outward
against flexible metal strips and moves the poles of the relay, D, between the contacts.

Figure 2-52. To look inside a sealed relay,
shave the top edges of the plastic package
with a utility knife til you open a thin crack.

Figure 2-53. Insert the blade of your knife

to pry open the top, then repeat the proce-

dure for the sides.

Figure 2-54. If you are really, really careful,
the relay should still work after you open it.

Figure 2-55

Figure 2-56. Patience is essential when

carving the edges of a relay package in

order to open it. Faster methods such as a

tomahawk or a flamethrower will satisfy the

emotional needs of those with a short atten-

tion span, but results may be unpredictable.

Figure 2-57. Four assorted 12-volt relays,

shown with and without their packages.

The automotive relay (far left) is the sim-

plest and easiest to understand, because

it is designed without much concern for

the size of the package. Smaller relays are

more ingeniously designed, more complex,

and more difficult to figure out. Usually,

but not always, a smaller relay is designed

to switch less current than a larger one.