Experiment 4: Varying the Voltage
26 Chapter 1
Using Ohm’s Law
Ohm’s Law is extremely useful. For example, it helps us to figure out whether a
component can be used safely in a circuit. Instead of stressing the component
until we burn it out, we can predict whether it will work.
For instance, the first time you turned the potentiometer, you didn’t really
know how far you could go until the LED burned out. Wouldn’t it be useful
to know precisely what resistance to put in series with an LED, to protect it
adequately while providing as much light as possible?How to Read a Data Sheet
Like most information, the answer to this question is available online.
Here’s how you find a manufacturer’s data sheet (Figure 1-68). First, find the
component that you’re interested in from a mail-order source. Next, Google
the part number and manufacturer’s name. Usually the data sheet will pop up
as the first hit. A source such as Mouser.com makes it even easier by giving you
a direct link to manufacturers’ data sheets for many products.VISH AY TLHG / R / Y540.
Vishay Semiconductors(^1922319223192231922319223192231922319223) e2e2e2e2e2e2e2e2 PbPbPbPbPbPbPbPbPb-freePb-freePb-freePb-freePb-freePb-freePb-freePb-free
High Efficiency LED in 5 mm Tinted Diffused Package
Desc ript ion
The TLH.54 .. se ries w as d evelo ped fo r stan dar d
appl ic ati ons l ike ge ner al ind icati ng a nd l ighti ng pur-
po se s.
It is h ous ed i n a 5 mm tin ted di ffus ed pl as tic p ack ag e.
The wi de viewing angl e of these devices pr ov ide s a
high on -off c ontr ast.
Several selectio n ty pes with diffe rent lu mi nou s in ten-
sities ar e o ffer ed. Al l L EDs ar e c ategor ized in lu mi-
nous i nte nsi ty gr oups. T he gr een and ye ll ow LED s
are ca teg orized addi ti ona lly in wa ve len gth gr oup s.
That allows us er s to assemble LEDs wit h uni for m
appe ar anc e.
Feat ure s
•Choi ce of t hree b right colo rs
Stan dar d T-1� pa ck ag e
Small m echan ic al to leranc es
Sui tab le for DC and h igh pe ak cu rren t
Wide v iewin g an gl e
Lumi nous int ens it y c ate gor ized
Yel lo w an d gr ee n c olor ca tego rized
TLH.54 .. wi th s tan d- offs
Lead -free de vi ce
Appl icat ions
Stat us li ghts
OFF / ON i ndicator
Background il lu mi nati on
Re ado ut l ights
Mainten anc e l ights
Lege nd l ight
Figure 1-68. The beginning of a typical data sheet, which includes all relevant specifica-
tions for the product, freely available online.
FundAmentAls
Ohm’s Law
For reasons I’ll explain in a mo-
ment, amps are normally abbrevi-
ated with the letter I. V stands for
volts and R stands for resistance
in ohms (because the omega
symbol, Ω, is not easily generated
from most keyboards). Using these
symbols, you can write Ohm’s Law
in three different ways:
V = I × R
I = V/R
R = V/I
Remember, V is a difference in
voltage between two points in a
simple circuit, R is the resistance
in ohms between the same two
points, and I is the current in
amps flowing through the circuit
between the two points.
Letter I is used because origi-
nally current was measured by its
inductance, meaning the ability to
induce magnetic effects. It would
be much less confusing to use A
for amps, but unfortunately it’s too
late for that to happen.