Display panel
On Sat, Oct 31, 2015 at 2:35 PM, Mike Stein <mhs.stein@gmail.com> wrote:
As Jon says, not really that complicated. Google
DIY LED signs for lots of ideas; e.g. one of mine
uses 75492 MOS LED drivers and 40158 shift
registers plus a few current limiting resistors and
driver transistors.

Don't forget to share the finished project!

From: "Jon Elson" <elson@pico-systems.com>

it really isn't that complicated.  The simplest
might be a byte shift register, ie. a bunch of
octal D-FFs like
the 74HC374.  Given a byte-wide group of GPIOs
on the Beagle Bone, you could send out 63 8-bit
with one additional GPIO to act as a clock for
the FFs.  The LEDs could be driven directly from
the FF outputs with a resistor.  With the
current generation of high-efficiency LEDs 10 mA
would be plenty of current, and so the FF
outputs would still be close enough the specs to
drive the next stage.  One downside of this
scheme is if the serial transmission was slow,
you'd see a blink each time the Bone sent a new
light pattern.

If you want to get more complicated, you could
have one HC374 for the shift register and one
HC374 as the latch.
You'd shift all 63 bytes through the byte-shift
register, pulsing the byte clock 63 times, and
then pulse the latch clock once to latch all the
5xx bits of light info into the latch register,
which would allow the LEDs to be updated without
any flash as the shift reg is being shifted.

Now, another way to do this is with
multiplexing.  You could maybe have 8 64-bit
words that loaded to a small RAM, and the RAM is
scanned to load data to banks of 64 LEDs.  This
reduces the number of drivers to, say, 64
cathode drivers and 8 high-current anode
drivers, but complicates the rest of the thing a
fair bit.  It will also cause the whole panel of
LEDs to flicker at the multiplexing rate, which
could be annoying when you flick your eyes
across the panel.

The 74HC595 8 bit shift register has a storage register also. You can cascade
> them then update the displays with a single pulse. I'm using them with
> ULN2803 8 bit drivers to drive the incandescent bulbs on my 360/30 panel.

I used three of these


that is the MCP23S17 as the inputs. A nice chip that’s 3.3v so compatible with modern FPGA and Raspberry PI and you get 16 lines per chip that can be set as in and out.
You can cascade up to four chips on a 4-wire interface as these can be addressed by a 2-pin address input.


Lawrence Wilkinson ljw-cctech@ljw.me.uk via classiccmp.org 

to General
On 31/10/15 21:11, Charles Anthony wrote:
What I don't know how to do is drive 500 or so LEDs.

I am guessing a bunch of shift registers, but I've pretty much reached my
design limits. I need some guidance on locating and understanding the
technology to run that many LEDs.

I have made a 60x120mm PCB which drives 64 LEDs using the
MAX7219 or MAX7221 driver. This has a 3-signal link (clock, data,
select/latch) and has a +5V supply.


Here is the bare board. I'm not in a position to supply boards, but
could provide the Eagle or Gerber files for anyone wanting to
manufacture them. I'm also happy to supply the schematics, though
there's nothing too special about them.


The boards can be daisy-chained so you only need 3 outputs to
drive any number of LEDs (depending on the update rate.)



Showing LED hookup to MCP23S17


GPBn ---> LED --> Resistor --> GND

Latching octal shift register: https://www.fairchildsemi.com/datasheets/MM/MM74HC595.pdf

Creating symbols in gschem https://ashwith.wordpress.com/2010/09/23/creating-your-own-symbols-in-gschem/

Timing diagrams: http://drawtiming.sourceforge.net/index.html

RPI3 GPIO pinouts: https://www.element14.com/community/docs/DOC-73950/l/raspberry-pi-3-model-b-gpio-40-pin-block-pinout

RPI3 GPIO docs https://www.raspberrypi.org/documentation/hardware/raspberrypi/spi/README.md

gschem tutorial: http://wiki.geda-project.org/geda:gsch2pcb_tutorial
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