10. The green laser may not work with the 9V battery;
a 12V supply is needed for it, and it will still be rather
dim using this circuit. The battery is removed when
hooking the circuit to 12 volts. The laser tester is
useful to take to the stained glass store and pick out
pieces of glass, or a laser pointer can be used for this.
Some of the components are only available in
surface-mount (SMD) packages. I designed a printed
circuit board (PCB; Figure 11) for expresspcb.com to
make for this. I consider myself relatively
inexperienced at surface-mount soldering, but this was
the only way to do it. I used through-hole components
where I could.
If you’re intimidated by SMD soldering, look at
some You Tube videos (search: SMD soldering), get
some flux, tiny solder wire and a tip, some type of
magnification, and dive in! It’s not that bad.
There are a few SMD resistors for space
considerations, but if you make it through the LED
The lasers are driven by constant-current LED
drivers. The circuit diagram has one driver circuit, and
the table shown in Figure 13 holds the values for the
individual parts of the circuit for each laser. The laser
drivers are supposed to have the components close
together, so the 330Ω resistors are mounted on the end
to get them in tight.
Some of the components are very sensitive to static
electricity. I used a bench anti-static soldering mat, a
grounded soldering iron, and a grounding wrist strap for
the placement of all the components. In theory, once
everything is soldered in place, the parts are not quite
The motors are speed controlled with DRV8870
chips. I originally thought I would vary the speed and
direction of the motors with the music
for even more variation in the display. It
turns out that the motors do not
respond fast enough to tell that any
changes are due to the music. The lasers
46 May/June 2018
■ FIGURE 11. The wired circuit board.
■ FIGURE 13. Table of values for the
seven LED laser driver circuits.
■ FIGURE 12. SMD parts "hold-down" of wire and fishing