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!

--
W J G

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