[sdiy] Fast lcd display like digitakt

[Spiros Makris]

I second the sentiment about the Adafruit library. They are easy to get you
going with experiments, but are notoriously clunky, and often make
less-than-ideal technical decisions. You might have to forgo some features
(such as printing images, certain shapes etc), but the majority of that can
be recreated if you need it I guess.
As you already found out, SPI is the fastest option, and you might even
experiment with increasing the SPI clock rate (in theory it can go up to
like 20Mhz); the maximum reliable rate you can achieve will be dependent on
the cabling/board and the display itself.
Since you already have a Teensy 4, I suggest you switch to that. Teensy LC
is not easy to source anymore, and the price difference is not worth the
loss in performance (4.0 can go up to 1Ghz if needed!). I suspect you will
not need it, but if you really want to squeeze out all possible performance
from your system, it pays off to look into hardware peripherals such as
DMA, which will save you some cycles for transfering data around etc.
Unfortunately, the protocols for those displays are not always
straightforward, so making your own library from the ground up might be too
much of a hassle (plus, you are locking yourself with a single display
controller). Some let you update only parts of the display, rather than
refresh the whole matrix every time, although it's not always laid out in a
convenient manner. A common approach is to build your menu screens in a way
that will avoid drawing stuff if it does not change, such as the title of a
menu, decorative graphics etc.
Using a display as feedback is awesome, however don't forget you can use
LEDs and toggle buttons as feedback mechanisms as well. Updating a series
of LEDs driven by a shift register is super fast (and you can use it with
the SPI you have currently, just sacrificing an extra GPIO for chip select)
and could save you some space and computation time on your display. Plus,
lights look cool!


On Sun, 16 Jun 2024 at 03:49, Benjamin Tremblay via Synth-diy <
synth-diy at synth-diy.org> wrote:

> I’ve been working on some virtual synth code, and also learning how to
> send nrpn midi messages. It’s all going well but for midi controller and
> synth projects I envision a paged Oled display with virtual knob animation
> and maybe a touchscreen.
> What kind of hardware do I need for this? I purchased 2” and 3” displays
> from Amazon and tried out sample code on an arduino mega and then ran it on
> a Teensy LC.  I have a teensy 4 and a pico and some Stm32F401 boards.
> I am using the Adafruit gfx library and so far using an offscreen canvas
> is too slow.
> Should I use a 1-bit display? Repainting the screens is sluggish; maybe
> 2fps max. Should I use a faster SPI implementation? I know teensy LC is
> slow. Should I use another graphics library?
> I’m going to assume displays are nice for things like waveform editing and
> such. I have seen some fast oscilloscope demos on Oled displays.
> Hm.
>
> Benjamin Tremblay
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