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BE ID
PR GIN EA
OJ NE L
EC R’
T! S
The Itsy-Bitsy
USB Lamp
Have you ever been in the delves of a computer and wished
you had some extra light? Here’s a great little USB-powered
lamp which you can build in next-to-no-time.
Words by Ross Tester
From an original design by Stan Swan
M
any readers will remember
a commercial product of a
few years ago, the “Itty Bitty
Book Light”. It was designed to clip
over the top of a book to give just a tiny
light on the page when, for example,
you were reading in bed and didn’t
wish to disturb your partner.
Times have changed. Now we’re all
working with computers. Many’s the
time I’ve been trying to look deep inside a computer and wished it was a bit
brighter so I could read type numbers,
see plug and socket orientations, check
board seating, and so on.
Sometimes, even a torch won’t work
because it’s too big to get really deep
down. You can't get that light where
you really need it.
Well, here’s the answer. We’ve
called it the Itsy Bitsy USB Lamp. It is
such a delightfully simple idea we’re
wondering why no-one ever thought
of it before.
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It started life (and continues) as a
student project at Massey University
in Wellington, New Zealand – and in
fact was submitted to us by the lecturer, Stan Swan.
When we say simple, we mean it:
just a USB plug on a suitable length of
cable, a superbright white LED and a
series resistor to limit LED current. The
LED and resistor are housed in an inline fuseholder (without its innards!)
which makes a superb little “wand”
and also protects the electronics, such
as they are.
Here’s what the Itsy Bitsy USB Lamp looks like: one end has an ultrabright LED
wired to a cable attached to a USB plug. It is as simple to build as it looks!
March 2002 37
You’ll be surprised by the amount
of light you get from the LED, especially if you spend a little bit more
and buy one of the really superbright
(8000mCd) models (eg, DSE Z-3982).
A cheaper, though lower light output
(2000mCd) is the Z-3980. The difference in price is significant, though:
$8.95 vs $3.95.
Of course, you don’t have to use a
superbright white LED. In fact, you
don’t HAVE to use a white LED at all.
This circuit will operate quite happily
with any colour and any brightness
LED – but you will probably be very
disappointed with the light output of
most LEDs. For best results, we really
do recommend the superbright white
types. Yes, they’re more expensive but
you get what you pay for!
The USB Port
In all modern computers, you will
find at least one, usually two and
often four USB ports. USB stands
for Universal Serial Bus, and is one
of the latest incarnations of methods
to get information in and out of your
computer.
pick one up for just a few dollars. A
local computer shop has a 1m USB
extension cable for $6 but you could
well do better than this at computer
fairs, swap meets, etc.
Here’s a tip: get together with a mate
and buy a male-to-male USB cable.
Cut the cable in half and you can both
build an Itty Bitty USB Lamp for half
the cost!
Strip back about 5cm of the outer
insulation and shield from the “bare”
end of the USB cable.
Normal USB cables have four wires:
red, white, black and green (as well as
the shield). The green and white carry
the data – we don’t need them so they
can be trimmed right back (make sure
the wires inside their insulation are
not exposed at all).
A tiny length of heatshrink tubing
over the ends of the green and white
wires will ensure that there cannot
be shorts, either to themselves, to the
shield wire or to the red or black wires.
Carefully bare about 2mm of the
insulation on the red and black wires.
Before we go too much further, open
up the in-line 3AG fuse holder and
remove the wires and spring inside.
All we want are the two plastic bits.
Slide the longer of the two pieces over
the end of the wire, smallest end first.
(You may need to drill or ream out the
hole a little to accommodate the wire
but don’t go overboard! Similarly, this
An ECU (that’s technical talk for extra
close-up) of a USB plug. It’s a male
plug which fits into the female USB
socket on the computer.
(For more details on the USB port,
refer to the article in the November
1999 SILICON CHIP).
We’re not particularly interested in
information transfer as such. But we
are interested in the fact that the USB
port offers power to external devices +5V is available on pin 1 (0V on pin 4).
Up to 100mA is available from the
USB port – far more than we need
for this little application. That’s the
reason for the series resistor. A 47Ω
resistor will limit the current to about
25mA – just about ideal.
Construction
The first thing you will need is
a USB cable with at least one male
plug on it. These are becoming fairly
common and you should be able to
38 Silicon Chip
Here’s the business end of the lamp,
fully assembled. The LED just pokes
its head through the cable hole in the
fuseholder.
might be necessary on the other bit of
fuseholder to accommodate the LED
when we come to it shortly.)
The photograph shows this well.
Slide the fuseholder down far enough
so it is out of the way.
Cut the anode lead (the longer lead)
of the bright white LED to about 3mm
long. Similarly, cut both leads of a
47Ω 1/4W (or even 1/8W) resistor to
about 3mm long and carefully solder
one lead of the resistor to the anode
It’s not exactly rocket science. . . but
it’s often the simplest of ideas that are
the best.
of the LED. The 47Ω resistor will
have a colour code of yellow, purple,
black, gold (or yellow, purple, black,
gold, gold if it’s a 5-bander). It can be
soldered either way around.
Cut a length of spaghetti insulation
(or some tiny plastic tubing) long
enough to cover the resistor and its
leads, then slide this over the resistor
so the connection to the anode is completely insulated. Heatshrink tubing
may also be used for this purpose, but
is not essential.
Cut another two short lengths of
insulation (say 5mm) and slide them
over the red and black wires of the
USB cable. Solder the red wire to the
resistor end and the black wire to the
LED cathode. By the way, spaghetti
insulation is not pasta . . .
Now slide the 5mm lengths of insulation over the solder joints – it is
important that the bits cannot short
out to each other when scrunched up
Parts List – USB Lamp
1 USB male plug moulded
to suitable length 4-way
screened cable
1 Ultrabright White LED (preferably at least 2000mCd) (eg,
DSE Z-3980, 3981, 3982,
etc)
1 3AG in-line 2-part plastic
fuseholder (eg, DSE P-7912,
Jaycar SZ-2015, etc).
1 47Ω 1/4W or 1/8W resistor
Lengths of thin diameter
heatshrink (preferably) or
spaghetti insulation
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inside their fuseholder “home”.
Strictly speaking, this assembly
should be fused in case of a short but
even it there is a short the USB port
will limit the current available. So
no fuse! (But it’s better not to have a
short anyway!).
Testing
Before going any further, check and
everything is OK, the white LED
should glow brightly. If not, check for
shorts or open circuits.
Final assembly
Slide the fuseholder back up the
USB cable, pushing everything inside
it until only the LED and abut 3mm of
its leads are emerging.
Slide the other end of the fuseholder
(the shorter end) onto the longer piece
so that the LED just pokes the top of
its head out the hole (flush with the
hole is fine).
Twist the fuseholder end onto its
body to lock it in place.
And that’s it. Now when you need
a bright light anywhere around your
computer – all you have to do is plug
it in to the USB port!
The labels
You might have noticed two labels
on the cable (hey, that rhymes!) in the
main photograph. They simply says
what it is and not to look directly into
the LED. We they were unnecessary
and therefore we haven’t shown them
SC
on the diagram above.
check again that everything is as it
should be. Most of all, make sure that
there is no possibility of any shorts
from one lead of the USB cable to
another – particularly the green and
white (data) wires. (Failure to do this
could damage your computer).
With your computer on, plug the
USB plug into the USB socket. If
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The final assembly of the lamp: it’s a pretty tight fit inside the fuseholder but it
does all go in. Just be careful that any exposed leads are insulated with heatshrink or spaghetti before sliding it in.
March 2002 39
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