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Date: 11 Dec 2002 16:20:26 -0000
From: Steve W.EE
Author-Address: stevew-ee nym alias net
Subject: Thanks!!! "Merry Christmas" decoration a success
I would really like to thank all the contributions I got
these groups, comp.home.automation and
sci.electronics.design. Due to the many helpful suggestions
we got the thing working yesterday
: I would like some ideas on how to make an automated
: flashing Christmas decoration. It has 14 small
: strings of 120-volt outdoor lights which spell out
: the words "Merry Christmas". What I want it to do
: is turn on one string of lights for each letter at
: about 1 second intervals to spell out the words then
: when all the lights are on it stays on for a couple
: seconds then they all turn off and it repeats the
: cycle. Sort of like the old "MOTEL" signs which
: were popular in the 60's.
#1 special thanks to Jerry Girard for the electronic
circuit design, it worked perfectly from the beginning.
I ordered most of the parts from Digi-Key, saving trees
from not having to open all those Radio Shack packages.
I made a few small changes to the circuit. I wanted it
to flash slower so on the 555 circuit the top resistor
was a 47K trimmer in series with 2K, the other resistor
4.7K and the cap 50uf. Remember there needs to be
a resistor in series with the trimmer to limit the
The trimmer pot can adjust the flash rate from about
1 letter every 2 seconds to about 5 per second. I set
it in the middle, about 1 per second which we prefer.
I took out the cap on the reset circuit. I prefer to
have all the lights go out at once and stay dark for
for a full second.
Where that cap goes I put a small push on/push off switch
this gives the option to keep all the lights on all the
time. I did the same thing back in '72 because my mother
thought the flashing lights were gawdy and didn't want
them flashing while they were having a big office
Digi-Key had a wide variety of opto's. I got some with
a 5-mil trigger current and increased those resistors
from 470 to 1K. The opto's have a zero-crossing
circuit which help cut down on interference. Since I'm
only running 20 watts through the triacs they will stay
cool without heatsinks.
I soldered the parts all in sockets on a small perfboard
doing point-to-point wiring on a 4x6 perfboard. I do
heed to learn how to make printed boards if anyone can
provide a few pointers I would appreciate it.
The whole controller went into a 5x7x3 plastic box.
Safety is based on the concept of double insulation there
is absolutely no exposed metal on the box. Also put a
small thermal fuse inside. The only holes for wires
to exit are on the bottom so the whole thing can easily
be covered for weather protection. Power supply inside
is a 9 volt DC wall wart tie-wrapped to the box. I used
one of the excess AC outlets from the light strings to
plug the wall wart into. 18-gauge stranded wire for the
connects is tightly tie-wrapped to the inside of the box
for strain relief.
For more safety, I installed a GFCI on one of the outlets
upstream from the outdoor one. The house was built in
1969 before these were invented.
The wooden display is built in 2 pieces, the word "Merry"
in red and "Christmas" in green with 1/4 inch holes drilled
about 3 inches apart for the lights. Back in '72 my
parents got the idea and drew the words in script on
a piece of plywood then cut it out.
The lights we used this year are the GE "Merry Midget"
mini lights which are about $2 per string of 100.
Another **BIG** thank-you to Jerry for his 2-word post
"Hot Glue". My dad got a glue gun for $6 and had a
real good time with sticking the bulbs in place, it
looks quite nice.
Back to the problem of the voltage on the lights. The
Merry Midget bulbs come in strings of 100, these are
broken into 2 groups of 50 bulbs in series, 2.4 volts
per bulb. Each letter on the display except for the
2 big ones uses from 10-17 lights. How do you power
the few bulbs in the display at the right voltage?
Back in '72 they were in groups of 20 6-volt bulbs
which made it a lot easier.
The idea with diodes got a lot of discussion but it
wasn't practical because it still would require 71
percent of the bulbs like 36 out of 50. Scratch
The idea of the transformer was good, power everything
at a lower voltage. 24-volt transformers are common.
But I really needed about 33 volts. The only 24 volt
one I could find cost about $90 and time was running
out. Scratch that one, too.
Now the idea with power resistors. They are hard to find
and there be a problem mounting them where they could be
insulated but still be able to give off heat.
I said I find a source of power resistors for 30 cents
apiece, but they'd be giving off unwanted radiation.
For those who haven't figured out, these "resistors" were
7-watt Christmas bulbs. The "unwanted" radiation would
be light. They would have to be hidden. I did some
tests, one thing I liked was that the big bulbs heat
up faster than the small ones, so the small ones will
turn on slower. This could work, but it turned out to
be tricky to get the right combination of big and small
bulbs to get the proper voltage. Also, the big bulbs
From this idea came even a better one and that's the one
I used. The Merry Midget lights are dirt cheap. What I
do is take the string of 100 and cut it into 2 strings
of 50. Take each string of 50 and stuff into the display.
Cut off the rest of it. Wire the remaining bulbs in
series with the display bulbs. Of course the voltage will
be perfect. And it's easy to stash the extra bulbs out
of sight. Each string of 50 draws 20 watts which works
out to 400 milliwatts per bulb. Each individual bulb
does not get very hot. The "excess bulbs" were
electrically in series with the display bulbs but
physically in a separate hidden place.
It took a lot longer to wire everything up than I thought
it would, about 3 days. The decoration is in two pieces,
one for each word. I mounted the controller right
behind the letter "C" in a central location. The two
pieces connect with 3 ordinary extension cords, this
provides 6 connections. They can be easily unplugged.
When I was building the circuit board, I stuffed loose
LED's into the opto sockets, they were various sizes
mostly red and green. It looked kind of neat. I built
a test fixture out of a string of large Christmas bulbs
with 14 lights. As I started putting in the optos and
triacs the LED's went away and the bulbs started
flashing. I left the controller on for a couple days
flashing the 14 white AC-powered bulbs. Then when
I started wiring the decoration the white bulbs went
out one by one and the real lights came on. A good way
of keeping track of which wire is which.
So it will be back for it's 30th anniversary, 1972-2002.
There are a lot of interesting comparisons between then
and now but I'll save them for a later post.
For me, it's one down and one to go. My next project
is to get lights to flash to music, with different
colors responding to sound frequencies. I especially
want the white lights to flash when the higher-pitched
Christmas bells rings. I've got 6 optos and triacs
Steve W. stevew-ee.nym@alias@net ( interchange . and @ )
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