Make Electronics

Experiment 8: A Relay Oscillator

66 Chapter 2

Important note: some breadboards divide each vertical column of holes, on

the left and the right, into two separate upper and lower sections. Use your

meter’s continuity testing feature to find out if your breadboard conducts

power along its full length, and add jumper wires to link the upper and lower

half of the breadboard if necessary.

Figure 2-74 shows how you can use the breadboard to replicate your oscillat-

ing relay circuit. To make this work, you need to apply the positive and nega-

tive power from your AC adapter. Because the wire from your AC adapter is

almost certainly stranded, you’ll have difficulty pushing it into the little holes.

A way around this is to set up a couple of pieces of bare 22-gauge wire, and

use them as terminals to which you clip the wire from the adapter, as in Figure

2-75. (Yes, you still need just a couple of alligator clips for this purpose.) Alter-

natively, you can use a breadboard with power terminals built into it, which is

more convenient.

S1

R1

S2

D1

D2

C1

12v

DC

Figure 2-74. If you place the components on your breadboard in the posi-
tions shown, they will create the same circuit that you built from wire and
alligator clips in Experiment 8. Component values:

D1, D2: Light-emitting diodes
S1: DPDT relay
S2: SPST momentary switch
C1: Electrolytic capacitor, 1,000 μF
R1: Resistor, 680Ω minimum

Figure 2-75. If your breadboard doesn’t have screw

terminals, insert two short pieces of solid-core

wire with stripped ends and then attach the

stranded wires from the adapter using alligator

clips.