■ THIS MONTH’S PROJECTS
Flashlight Evolution . . . . . . . . .32
RF Impedance Analyzer . . . . . . 38
Metal Detector . . . . . . . . . . . . . 50
■ LEVEL RATING SYSTEM
To find out the level of difficulty
for each of these projects, turn
to our ratings for the answers.
●●●● . . . . Beginner Level
●●●● . . . . Intermediate Level
●●●● . . . . Advanced Level
●●●● . . . . Professional Level
years, with the
advent of white
LEDs, the ubiquitous
household item —
flashlight — is
It caught my attention
when I noticed the
many benefits LEDs can
bring about; especially
efficiency and the
Using just a few components, you can
easily transform the traditional bulb
flashlight into an energy-saving, super
bright LED flashlight.
Istarted to think about and work
on how to transform all of my
traditional bulb flashlights into LED
flashlights. The outcome actually
turned out to be quite encouraging
and rewarding, and the costs were
minimal. I’d like to share some of
my experiences with you here.
White LED Parameters
The main players in this flashlight evolution are the white LEDs.
They are the newest members in the
LED family, and super bright white
LEDs are still expanding.
White LEDs differ from the
normal signal indicator LED in several ways, but the most important
parameters are these three: forward
voltage VF; the corresponding forward current IF; and luminous intensity measured in millicandela (mcd).
Most white LEDs are typically
listed as VF = 3. 2-3.6V, IF = 20 mA;
their luminous intensities can range
from 3,000 to 30,000 mcd with
associated ascending prices. For
■ FIGURE 1.
es here, most 6,000 to 9,000 mcd
LEDs are adequate.
Also keep in mind that not all
LEDs are created equal. Even if you
buy the same batch of LEDs from
one source, each LED may have
slightly different forward current
under the same forward voltage;
hence, different brightness.
For this reason, it’s better to
measure each LED’s VF and IF
before using them. Figure 1 is the
simple regulated power supply
circuit to do so. It uses the LM317
regulated IC. Its output voltage
VO (volts) can be approximately
calculated by the following formula:
Vo = 1.25 (1 + R1/R2)
For instance, using R1 = 500Ω
trimmer potentiometer and R2 =
100Ω, the highest output voltage
should be VO = 1.25* 6 = 7.5V.
Therefore, you can reduce the trimmer resistor value to get any regulated voltage between 3.0V to 4.5V
at the output for your experiment.
My First LED
My first LED flashlight was a
very simple one. I didn’t change