Tricolor LEDs create a flashing array
Create a colorful display with red, green, blue LEDS controlled by oscillators and counters.
Jeff Tregre, www.BuildingUltimateModels.com, Dallas, TX; Edited by Martin Rowe and Fran Granville -- EDN, June 24, 2010
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You can build a matrix of RGB
(red/green/blue) LEDs using a simple
and inexpensive circuit comprising the
control logic and driver circuit in Figure 1 and some LEDs (Figure 2). The center
RGB LED is the first to come on, after
which each sequential LED in the 8×8-LED matrix follows. This process gives the
appearance that the display is alive and
moving outward. This sequence repeats,
producing a rainbow effect of colors.You can adjust the frequency of each
clock by changing the values of R17,
R19, and R23. Use different frequencies
for each clock, which will display eight
colors from the 65 
tricolored LEDs, because
using the same frequencies for all
the clocks causes your display to appear
white. The cost of building this circuit should be $25 to $30. You can purchase
100 5-mm RGB LEDs from eBay for a
total of about $18. Be sure to use common-
cathode LEDs.
tricolored LEDs, because
using the same frequencies for all
the clocks causes your display to appear
white. The cost of building this circuit should be $25 to $30. You can purchase
100 5-mm RGB LEDs from eBay for a
total of about $18. Be sure to use common-
cathode LEDs.This simple circuit comprises three
clocks and three counters, one for each
of the three LED colors. Setting each
clock frequency to a different rate causes
each color of each LED to appear to be
random. All resistors are 0.25W, except
for R3, R8, and R13, which are 0.5W; R4,
R9, and R14, which are 1W; and R5, R10,
and R15, which are 1.5W resistors. These
high-wattage resistors and the 12 NPN
transistors are necessary because all LEDs
in this matrix, except the center one,
connect in parallel. Start by bending all
of the ground leads flat and connecting them together. When wiring the LEDs,
begin in the 
center and work outward.
You can then mount the LED board
onto the top of the PCB (printed-circuit
board). Figures 3-7 and this video show the circuit in action. See Table 1 for a parts list.
center and work outward.
You can then mount the LED board
onto the top of the PCB (printed-circuit
board). Figures 3-7 and this video show the circuit in action. See Table 1 for a parts list. To add the finishing touches to your
project, use a small picture frame and install
waxed paper onto the inside of the
glass. Mount the LED board ¼ to 1 in.
away. The magnifying lens of the LEDs
will produce a beautiful effect when they
shine through the waxed paper.
Talkback
-
I would like to find out from the author if he could suggest any practical application he might have thought of.
Jyoti Pakrashi - 2010-16-11 09:07:59 PST -
We did not have tri-color LED's in 1985, but really is this the best we can do? Give me some NOVEL circuits!
george Bush - 2010-27-7 12:37:35 PDT -
Where was the video of the circuit in action?
Gadget Freak - 2010-21-7 16:58:57 PDT -
Seriously? Welcome to 1985... How about some articles on circuits that are actually useful?
Bob Barker - 2010-1-7 12:47:17 PDT -
Because the led sections are in parallel it would not take that very long to wire, although a PCB would speed the process quite a bit. Using a microcontroller assures that the life of the design would be very short, since they become obsolete and unavailable in a short time. I imagine that the display is pretty, but can't figure out the practical application. It may make a pretty night-light, I suppose. IT would have been nice to be able to see the actual circuit of the device.
William Ketel - 2010-29-6 07:09:29 PDT
