RK11-C indicator panel inlays?

Mike Katz bitwiz at 12bitsbest.com
Mon Dec 6 16:55:41 CST 2021


I completely agree with reducing the strip size.

One of my projects is a redesign of Oscar Vermilion's PiDP-8/I using 
addressable LEDs.  I was thinking of breaking the 88 LEDs into separate 
strands based on function (step counter & Multiplier Quotient [17 LEDs], 
accumulator and link [13 LEDs], Memory Buffer [12 LEDs], Memory Address 
[12 LEDs], Data & Instruction Fields and Program Counter [18 bits], 
Instruction & States [17 :LEDs]).  That would require 6 GPIOs.

I don't know if the PIO can handle 6 separate GPIOs like that but it's 
worth a try.


On 12/6/2021 3:05 PM, Ethan Dicks wrote:
> 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
> Definitely
>> 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.
> -ethan

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