[sdiy] Arpeggiator1 / Arduino UNO

[Rick Jansen]

No idea, and I don't care :-) All I want is 12 discrete voltages per octave. As far as I 
can tell, without actually measuring, the voltages are reached quick enough, and are 
repeatable.

The arpeggiator code has a list of 48 values, one for each pitch. You can tweak each value 
to obtain the perfect pitch, eh, voltage.

So, this is not a DAC where changes from 0x40FF to 0x4100 or 0x4000 to 0x3FFF are an 
issue. And if they are I'll use a chip.

I'm quite happy to have found this componentless solution, as I did not have a DAC (well, 
I have an old ZN426), and it was Easter, so no shops were open..

rick


On 10/04/2015 10:08, Roman Sowa wrote:
> How does your 8+8 bit PWM DAC perform in terms of DNL at the MSB
> boundary? I mean when for example it goes from 40FFh to 4100h, as well
> 4000h to 3FFF.
>
> Roman
>
> PS. I put so many tehnical sounding mumbo jumbo in first sentence that
> it sounds even funny :)
>
> W dniu 2015-04-10 o 01:03, Rick Jansen pisze:
>> 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
>>
>>
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