Folderol  wrote:
> On Wed, 04 Sep 2019 10:34:21 GMT
> Alister  wrote:
>
>> On Tue, 03 Sep 2019 13:06:58 -0400, Dennis Lee Bieber wrote:
>>
>>> On Tue, 3 Sep 2019 07:39:14 -0400, "J.B. Wood" 
>>> declaimed the following:
>>>
>>>> Hello, all.  Just thought I'd revisit this topic since it's been a
>>>> while.  Has anyone ever constructed a Pi-based standalone 1-2 channel
>>>> MIDI sequencer?  By standalone I mean it has an integral display and
>>>> required pushbuttons/rotary knob for device control.
>>>>
>>> What do you intend to show on the display?
>>>
>>> What type of control do you envision? (If you visualize a one/two
>>> octave keyboard, you then have to specify how many notes in parallel --
>>> one note at a time can use a simple row/column keyboard scan -- but when
>>> you go beyond two notes such a matrix can generate ghost key presses;
>>> avoiding ghosts requires a linear matrix, which means LOTS of GPIOs -- a
>>> 1x24 would need 24 GPIOs to detect key presses, while a 4x4 is only
>>> using 8 GPIOs for 16 keys)
>>
>> Not Necessarily so. To eliminate ghosting you simply need a diode on each
>> switch (how do you think a quality computer keyboard manages N Key
>> rollover?).
>> 16 io pins gets you 8*8 = 64 keys so a full piano (81 keys if i remember
>> correctly) still only requires 9 by 9.
>>
>>
> You need more than that to allow for various switches/selectors etc.
> Also you need to scan the matrix as fast as possible, preferably in the tens
of
> microseconds range. However, just to make it 'interesting' you should include
> some form of debounce mechanism.
> Been there, done that, T shirt worn out!

Since sound only travels one foot per millisecond and most musical
instruments (and all groups) are bigger than that, scanning resolution of a
millisecond or so should be undetectable.

--
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

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