RK11-C indicator panel inlays?

Ethan Dicks ethan.dicks at gmail.com
Mon Dec 6 15:05:29 CST 2021

On Mon, Dec 6, 2021 at 10:36 AM Mike Katz via cctalk
<cctalk at classiccmp.org> wrote:
> One dumb suggestion to make it easier to control 144 lamps is to use
> addressable LEDs.  You can control them in banks or all in a single
> serial line.  If you use a single line you can control all of them with
> just 1 GPIO.
> Each LED requires 24 bits of data.  That would be 3,456 bits.  The
> WS2812B has a 300uS low start indication and 1.25 uS per bit.  That
> would mean it would take. 4.62mS to update the all of the LEDs.

If 200Hz isn't fast enough for updates, and you have more GPIOs, you
can implement this as, say, 4 strands and write out nybbles.  There
are cheap video wall that use MCUs with DMA engines and pump out 8
strips at once.

> Since these are tri-color LEDs you can control the color and simulate
> incandescent lamps


> Another advantage to the LEDs is once they are set, you don't have to
> talk to them again until you need to change something.

Yep.  Self-latching.

> I am going to use a Raspberry Pi Pico RP2040 CPU's PIO co-processor to
> drive the LEDS from a 432 byte array in memory.  All I do is update
> which LEDs I want to change and the PIO DMAs the entire array to the LED
> chain once every 10mS (or slower depending on need).

Sounds like a great approach.  I have a couple of Picos but haven't
dug into the PIO engines yet.

I've been working with WS2812B LEDs for a while now and enjoyed
watching the cost per LED plummet from a few years ago.


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