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!
Many 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
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
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.
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 in-line fuseholder (without its
innards!) which makes a superb little "wand" and also protects the electronics,
such as they are.
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.
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
Here's the business end of the lamp, fully assembled. The LED just pokes its head through the cable hole in the fuseholder.
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
(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
will limit the current to about 25mA - just about ideal.
It's not exactly rocket science. . . but it's often the simplest of ideas that are the best.
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 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
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
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 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 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.
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.
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
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
Before going any further, check and 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 everything is OK, the white LED should glow brightly. If not, check for
shorts or open circuits.
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!
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|