Nuts and Volts - May/June 2018

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.

Electronics

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 so sensitive.

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