FIGURE 2. This schematic shows you how to build the VEX strobe light. This strobe light is lower cost, much safer and easier to build,
and should not take more than one evening to put together. It uses very few parts in its construction and can drive up to eight independent
bright white LEDs. Notice that there is no need for a high voltage driver circuit, large capacitors, or even a xenon flash, using one or more
bright white LEDs and some discrete components. Instead, we use a ULN2803 driver that was discussed in a previous SERVO article.
faucet.) The strobe light flash rate (frequency) can be varied
using many kinds of sensors including potentiometers,
quadrature optical encoders, and rotary encoders. For the
purposes of this experiment, we will use the VEX quadrature
optical encoder, although the potentiometer would work just
as well. A standard optical encoder is not recommended since
it cannot detect the direction that the control knob is turned
by the operator. The flash rate can be easily controlled using
the PIC18 C or Easy C Wait() statement (available from
www.vexrobotics.com/products/programming/
TABLE 1. Bill of Materials required to construct a VEX
strobe light with up to eight bright white LEDs.
QTY DESCRIPTION SOURCE
1 VEX microcontroller Innovation First, Inc. www.vexforum.com
2 1 Innovation First, Inc. www.vexforum.com
3 2 SparkFun www.sparkfun.com
4 1 RadioShack www.radioshack.com
5 1 SparkFun www.sparkfun.com
6 1 Hardware Store
7 1 Innovation First, Inc. www.vexforum.com
8 1 Innovation First, Inc. www.vexforum.com
9 1-8 Bright white LEDs SparkFun www.sparkfun.com
10 1-8 100 to 470 ohm resistors RadioShack www.radioshack.com
11 1 VEX pushbutton switch Innovation First, Inc. www.vexforum.com
12 1-8 *Toggle switches RadioShack www.radioshack.com
13 1 RadioShack www.radioshack.com
14 1 Office Supply Store
ITEM
1
VEX 9. 6 volt battery
ULN2803 inverted
octal driver
Wire-wrap cable
*Package of
jumper cables
Flashlight or lantern
VEX quadrature
optical encoders
*VEX potentiometer
9 volt alkaline battery
Circular protractor
(0-360 degrees)
*Items are optional.
64 SERVO 08.2011
mplab.html, www.vexrobotics.com/products/
programming/ easyc-pro.html, and www.vexforum.com/
wiki/ index.php/Software_Downloads).
Building The Strobe Light
The schematic shown in Figure 2 shows you how to build
the strobe light. This version is low cost, much safer and easier
to build, and should not take more than one evening. It uses
very few parts in its construction and can drive up to eight
independent bright white LEDs. Notice that there is no need
for a high voltage driver circuit, large capacitors, or even a
xenon flash. Instead, we use the ULN2803 driver that was
discussed in the stepper motor article in the Oct ‘ 10 issue of
SERVO, a pushbutton switch, a VEX quadrature optical
encoder, one or more bright white LEDs, and some discrete
components. The complete bill of materials for this experiment
is shown in Table 1. The single bright white LED shown in
Figure 3 should be mounted so that it is kept away from any
flammable materials since it can get very hot. The completed
VEX strobe light using only a single bright white LED flashing
brilliantly is shown in Figure 4. It can easily be expanded to
handle up to eight flashing LEDs with enough light to brighten
any party, however. Using a recycled flashlight or lantern
reflector to reflect the strobe light, mount the bright white LED
in the place where the original bulb used to be. The diameter
of the reflector should be between 2” to 6” to insure that the
maximum flash is reflected around a room. The flashlight may
be returned to its original working condition after you are
done with this experiment.
CAUTION: Don’t stare directly at the bright white LEDs or
touch them since they can get hot while operating. Also be
aware that flashing lights have been known to cause epileptic
seizures in individuals who are susceptible to them. If you
know of anyone with this condition nearby, then do not
operate the strobe light. If you start feeling dizzy or
disoriented, then turn the strobe light off and do not use it.
