6 Dec
2021
6 Dec
'21
2:55 p.m.
Ethan,
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.
?????????? Mike
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