Make Electronics

Experiment 6: Very Simple Switching

48 Chapter 2

FundAmentAls

All about switches (continued)

Sparking

When you make and break an electrical connection, it tends

to create a spark. Sparking is bad for switch contacts. It eats

them until the switch doesn’t make a reliable connection

anymore. For this reason, you must use a switch that is ap-

propriate for the voltage and amperage that you are dealing

with. Electronic circuits generally are low-current, and

low-voltage, so you can use almost any switch, but if you are

switching a motor, it will tend to suck an initial surge of cur-

rent that is at least double the rating of the motor when it is

running constantly. You should probably use a 4-amp switch

to turn a 2-amp motor on and off.

Checking    a   switch

You can use your meter to check a switch. Doing this helps

you find out which contacts are connected when you turn

a switch one way or the other. It’s also useful if you have a

pushbutton and you can’t remember whether it’s the type

that is normally open (you press it to make a connection) or

normally closed (you press it to break the connection). Set

your meter to measure ohms, and touch the probes to the

switch terminals while you work the switch.

This is a hassle, though, because you have to wait while

the meter makes an accurate measurement. When you just

want to know whether there is a connection, your meter

has a “continuity tester” setting. It beeps if it finds a connec-

tion, and stays silent if it doesn’t. See Figures 2-30 through

2-32 for examples of meters set to test continuity. Figure

2-33 offers an example of a toggle switch being tested for

continuity.

Use the continuity-testing feature on your meter only on

circuits or components that have no power in them at the

time.

Figure 2-30 Figure 2-31 Figure 2-32. To check a circuit for conti-

nuity, turn the dial of your meter to the

symbol shown. Only use this feature

when there is no power in the compo-

nent or the circuit that you are testing.

Figure 2-33. When the switch connects two of its terminals, the meter shows zero

resistance between them and will beep if you have set it to verify continuity.