An oldie but goodie, the
LM3914 is still being
manufactured today and
serves as the heart and soul
of our desktop rocket.
Desktop fireworks is one
of the simplest applications
for the LM3914 as presented
in the manufacturer’s
technical datasheet (NOTE:
The Texas Instruments
LM3914 technical datasheet
was used during the
development of this project),
with just one resistor used in
the circuit. Adding to this
solitary resistor are two
blinking red LEDs which will
be used as replacements for
the final LED in the bar graph
(LED 10). In other words, rather than the LM3914 lighting
LED 10 in the bar graph, the two blinking LEDs will be
triggered. Figuratively, these blinking LEDs serve as the
explosion of the aerial shell that typically culminates the
launch of a rocket.
In order to gain the maximum impact with desktop
fireworks, the entire circuit is mounted on a piece of
lightweight corrugated cardboard stock and is cut into the
shape of a rocket. Here is where you can get creative and
let either whimsy or realism guide your rocket design.
Regardless of your creative direction, however, remember
to cut slots into the base of your rocket and on an extra
set of fins. These two slots in the rocket and fins can then
be slid together (forming a “+” base) for keeping your
rocket on the “launchpad,” enabling you to ignite a
desktop fireworks display at a moment’s notice.
After you’ve mounted the circuit on your cardboard
rocket base and installed a 3V lithium battery, operation is
as easy as 3-2-1, FIRE! First, flick the SPDT power switch;
you’ve just lit the fuse. Slowly rotate the potentiometer;
the rocket streaks skyward. When the top two LEDs
remain lit (remember, the last LED — LED 10 — is NOT
connected to the LM3914; instead the two blinking LEDs
will act as the “last” LED), rotate the pot two more
“clicks.” The rocket explodes with bombs
bursting in air. If you leave the final blinking
LEDs powered, they will slowly ebb in and
out of synchronization in a nice soothing
Step by Step
1. Push the LED bar graph’s leads
through the cardboard rocket until they
protrude through the back.
2. Snip off the top, LED 10, cathode, and
anode pins from the LED bar graph display.
July 2014 45
■ Our desktop fireworks being tested on a breadboard.
Note: The SPDT switch has not been added yet.
ITEM COST SOURCE
LM3914 ($1.95; SparkFun Electronics)
10-position LED bar graph ($1.95; SparkFun Electronics)
( 2) Blinking red LEDs ($. 70 each; Mouser)
5K potentiometer ($1.50; Mouser)
SPDT switch ($1.50; SparkFun Electronics)
Coin cell battery holder ($1.25; SparkFun Electronics)
3V lithium battery ($1.95; SparkFun Electronics)
Hookup wire Prices subject to change without notice.