Nuts and Volts - September 2017

future features like mods and patches to its musical instrument digital interface (MIDI) and multi-note polyphony (e.g., more than two-note).

MIDI of the Road

Speaking of MIDI, while the Macchiato kit is currently able to respond to Note and Velocity information via an attached MIDI controller, Marshall Taylor at SparkFun Electronics has created a GitHub repository that contains Arduino code for MIDI splitting, testing, and bending that could be used for experimenting with the Synth kit. You can locate his code at github.com/marshalltaylorSFE/ ArduinoSynthMidiFilter.

Can Touch This

Meanwhile, back at the kit ... there are two additional features that make the Macchiato Mini Synth more than just a sum of its parts. For one, what good is a synthesizer without a keyboard, right? Well, Teenage Engineering has made a formidable product line of “pocket-sized” synthesizers as shown in Figure 5 with nary a keyboard in sight. Ranging from $50-$90, these calculator-looking devices claim a “wall of sound,” but this ain’t Phil Spector, baby. Sure, they might be fun to fiddle around with, but two-note polyphony, U Can’t Touch This.

The Mini Synth comes with a one octave keyboard and it’s hiding right in plain sight. Unlike a conventional keyboard with ebonies and ivories that you can tickle, this dirigible kit has a “wunder-weapon” capacitive touch keyboard that is built smack dab into the PCB (see Figure 6). It works great, but there are a couple of caveats. Straight from the Zeppelin Design Works Quick-Start Guide, you can play a low note “drone” along with an accompanying melody by tapping on the lower note key and then playing the melody as a staccato. This playing tip can be enhanced by adding a long decay.

The second caveat continues along this drone action by setting a similar low octave drone, but then switching to a higher octave and playing a melody. We mention these points as “caveats” because we were unable to achieve satisfactory results during our testing.

Naturally, practice makes perfect and these two keyboard tricks could be added to your playing arsenal with apt application of deft digit dexterity.

Dial-A-Song

While the capacitive touch keyboard might be a giant feature of the Macchiato Mini Synth, the nine adjustable potentiometers just might steal the show. As you can see in Figure 7, lined up in an easily accessible row above the keyboard, these nine pots are anything but stock current adjusters.

First off, these fancy pots don’t require knobs for operation — the knob is built right into the shaft. How often is “getting the shaft” such a good thing, right? Well, uglying up the design aesthetic with a bunch of “chicken head” knobs would certainly make this synth less appealing.

Second of all, these pots control the generation of the circuit’s waveforms and its low frequency oscillator (LFO) and low pass filter (LPF). There are nine controls that you can apply to the Macchiato Mini: (from left to right) wave shape (sine, triangle, sawtooth, and square); octave (1-4);