Even when the source is removed, some electricity might remain. To be
absolutely sure, before you touch anything, test the circuit with your multi-
meter. (We talk about how to use a multimeter in Chapter 4.) And don’t take
somebody else’s word that the power is off; always check and double-check
this yourself!Don’t work with AC-operated circuits unless you absolutely have to. And if
you do, it might not be a bad idea to have a friend nearby who is trained in
CPR. Visit http://www.redcross.orgfor more information about CPR training.Protecting Electronic Components from Dreaded Static Discharge........
You’re not the only thing in your work area that could suffer from shocks. Static
discharge (also referred to as electrostatic discharge; ESD) can do damage to
your delicate electrical components. Static discharge is so named because it’s
caused by the discharge of electrons from a static charge that hang around in
an insulating body, even after the source of those electrons goes away.Static charge is typically caused by friction. You might trap some electrons in
your body as you walk across a carpet, for example. When a static charge is
built up on your body, a corresponding voltage difference is built up between
your body and a grounded object, such as a doorknob. The zap when you
then touch a doorknob is the static discharge: that is, the electrons flowing
from you to the doorknob.What static discharge can do .............................................................
Metal oxide semiconductor (MOS) devices are cool because they allow inte-
grated components to use less power. MOS devices improve circuit design
and operation, but that improvement comes at a price. These little guys are
VERY sensitive to ESD. One little zap, and they are likely to be history.When you walk across a carpet, you can produce a static charge in the range
of 2,000–4,000V. Because the number of electrons trapped on your body is
low, you feel only a little shock. However, MOS devices contain a very thin
layer of insulating glass that can become toast when exposed to as little as
50V of discharge or less. When you work with a MOS device, your body, clothes,
and tools have to be free of static discharge. (You find out how to do that in the
next section.)Chapter 2: Safety First 21