Hardware Reference
In-Depth Information
Now all you need to do is mount your light strips in some way - maybe a display board above
the decks, or hanging down from the ceiling. I mounted the eight strips on a 8 x 10-inch
piece of MDF painted black. I arranged them in a fan shape over half a circle. This would
stand up nicely under my monitor. The display is startlingly different depending on what you
put in front of the LEDs. If you use nothing, they are very raw but do shed a lot of light. A
thin styrene sheet of 0.5mm or less thickness acts as a good diffuser if placed close to the
LEDs. However, if you set it just a few inches in front of them the diffusion is much greater
and you no longer see the individual lights but bars of colour. Finally another good diffuser is
a few layers of clear bubble wrap, the round bubbles in it nicely complementing the individ-
ual round LEDs. Your imagination and design skill coupled with your venue will allow you to
put these strips, be they short or long, into many a pleasing configuration. However, if you
want to cover the dance floor with them you will have to install them behind acrylic sheets to
prevent their being stamped on.
Making the Lights Move
Now so far you have looked at stepping the sequence along using the internal timers or an
external push button, and if that is as far as you want to take this project, then fine. However,
the next step is to have the music drive the change in sequence. Unfortunately this may not
work as well as you might be expecting, but you can make a good stab at things relatively easily.
An audio signal, the sort that comes out of an MP3 player or from record decks, is a very
complex waveform, consisting of lots of very rapid changes. The speed of the rapid changes
carry the frequency content information of sound. The size of the waveform - that is over
what range of voltage values they cover - is the amplitude or loudness information. However,
the amplitude is varying rapidly to convey the frequencies. What you need to do is to isolate
the loudness factor - that is to measure just the size of the peak of the waveform, but it is
not quite as simple as that. With a loud sound you get a large positive value and a symmetri-
cally large negative one, so in order to get a measure of loudness you have to ignore the nega-
tive value and hold the positive value at its peak. Such a circuit is possible and is called, rather
unsurprisingly, a
peak detector.
Now the beat of music is normally carried in the low frequencies. There are electronic circuits
that will separate or filter a mishmash of frequencies so that only a specific range of frequen-
cies get through. The two simplest type are known as
high pass
and
low pass.
In a low-pass
filter only the low frequencies can pass through it. Exactly how low is low depends on what is
known as the filter's
break frequency.
This is defined as the frequency where the output is cut
down by half compared with the input. By correct choice of components you can make this
break frequency any value that you want. Most of the low frequencies in music are between
200Hz and 30Hz - any lower and you tend to feel it more than hear it. So to get at the beat
