[sdiy] Arpeggiator1 / Arduino UNO

[Rick Jansen]

Hi all,

Well, at long last I'm a bit back to synth-diy-ing. Here is my first Arduino UNO based 
project: an arpeggiator: <http://dropmix.xs4all.nl/rick/Emusic/Arpeggiator1/>

It serves two purposes: 1. getting to know the Arduino, and 2. finally using that 1-octave 
piece of keyboard that was in a box for 20 years.

It's still in the breadboard phase, as a tryout for the upcoming sequencer, but it works, 
and I'm having a lot of fun with it.

A longer writeup, images and sketch are in the web page

   <http://dropmix.xs4all.nl/rick/Emusic/Arpeggiator1/>

Here are some keywords:

- I2C 8574 ic's as in/out expander: 2 chips to read the 12-key 1-octave keyboard, 
interrupt based; 4 bits spare;
- I2C 8574 ic's as LED outputs: 12 LEDs, one per key, displaying the note playing as a 
sequencer; 4 bits spare;
- Can easily be expanded to 64 keys in + 64 LEDs out, or 128 things in or out, or 
whatever. (I2C is great!)

- ~16 bit "DAC" without a DAC: using two PWM pins combined, and RC-filters, to produce the 
control voltage;
- gate signal; gate may be shorter than the note duration for "staccato", etc;

- TimerOne interrupt based timing, 120BPM, 24 ppqn, like midi does, if I understand that 
correctly;

- sequence mode: up / down / up-down / random ;

- For each note there's a pitch, a duration and a gate duration, internally, although for 
the arpeggiator note and gate duration are currently fixed value (all quarter notes, @ 24 
ppqn)

- Operation:
1. press START
2. press one or more keys of the keyboard
3. while you keep the keys pressed the machine loops through the corresponding notes
4. press STORE to store the melody; you can now release the keys
...
8289. press STOP

rick