The ATmega328 is preloaded with the Optiboot bootloader and the current version of the MintySynth software. Revision 2.0 runs at 3V (or 5V if powered by a 5V FTDI cable) and is overclocked at 16Mhz. All but two of the pins on the ATmega328 are used, and the unused ones (D12 and D13) are broken out for possible expansion. The potentiometers are on pins A0-A4, and the photocell is on pin A5. The battery level is monitored internally. The audio output has a low-pass filter and a series capacitor to remove DC offset. The circuit is designed to be a line out, so with headphones the volume may be somewhat limited and the sound quality is best if you use amplified PC speakers, a home stereo, etc. You could also use an external headphone amplifier. A sound system with good bass reproduction (e.g. powered computer speakers with a subwoofer) is great, because one of MintySynth's strong suits is its bass! The three-pin header in the upper-left corner was designed for sending MIDI signals to other devices (see the f.a.q. for more information).
My goals were to:
MintySynth uses all through-hole components to make soldering easy, and if you have a little experience soldering (or are willing to learn!) assembly is straightforward. I chose thumbwheel potentiometers after some experimentation with other types because they have a minimal footprint yet are responsive and easy to turn, even in the limited space. The thumbwheels and buttons are supported securely by the CNC-cut acrylic cover plate.
To program MintySynth yourself (not necessary if you're using the preloaded software) you'll need an FTDI cable, available at Sparkfun or Adafruit. The first time you use it you'll need to install the drivers. Contrary to the directions, you may have to set "Set RTS in Close" in Windows, mentioned at the bottom of the page here. After that, you can program it just like an Arduino Uno. It should reset itself when you upload sketches.