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Appendix A
AC AND DC POWER SOURCES
On page 15 we already gave some information about the battery power source, but...
there is more to explain about this item. The voltage of a battery is a quite low DC
voltage. It is not dangerous when you touch it. The mains power voltage on a wall
socket in our homes however is a VERY DANGEROUS AC voltage of 120 or 230 Volts
(depending on the country you live in).
You already know and may understand that
you must never make contact with this dangerous household voltage (mains
power).
We introduced 2 new terms, AC and DC, which are abbreviations of Alternating Current
and Direct Current (also called continuous current).
AC MAINS power is often called household power or household electricity. The direction
(polarity) of the AC voltage changes periodically. Mostly, the shape of such voltage is a
sinus waveform.
Picture of a sine wave voltage:
The dotted line shows a DC voltage
The DC power is a constant voltage with a constant polarity. DC voltage is supplied by
all kind of batteries like radio, MP3 player and even big car batteries. They all have a
DC voltage.
In this manual and in electronics in general, we use the SI-prefix a lot. It is a way to
present the unit of measure of a quantity or value with a lot of zeros.
For example weight; Kilo (K) means 1000 so 1 Kg means 1000 grams.
Important prefix are;
M =
Mega = 1000 000
K =
Kilo = 1000
m =
milli = 0.001
µ = micro = 0.000 001
N = Nano = 0.000 000 001
P = Pico = 0.000 000 000 001
1.5 Volt battery
Type AA or AAA
SI-Prefix
