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can the prop be cascaded to control thousands of LEDs? — Parallax Forums

can the prop be cascaded to control thousands of LEDs?

StefanL38StefanL38 Posts: 2,292
edited 2012-01-07 00:50 in Propeller 1
This is a question especially @Timothy (BrillDea)

Could the prop be cascaded to control such an amount of LEDs?

Smack Nightclub - LED Room

best regards

Stefan

Comments

  • Jack BuffingtonJack Buffington Posts: 115
    edited 2010-10-03 09:36
    Yes. I've done it. Specifically, I'm controlling 7680 LEDS (2560 RGB LEDs) from a single propeller. One propeller captures video from a VGA source and sends it over a high speed serial line to 40 other propellers, each controlling 64 RGB LEDs. I'll show it off when I am allowed to but for now I'm under a NDA. The cool thing is that I have a lot more bandwidth left to control more LEDs. I probably could have controlled about 13,000 RGB LEDs from a single serial line and the prop is capable of capturing a lot more data than that so if another serial line was added then it could really get ridiculous.
  • Mike GreenMike Green Posts: 23,101
    edited 2010-10-03 10:02
    The simple answer is yes. There are many ways to do this. If you want something simple and cheap that just turns LEDs on and off, you could use lots of TPIC6595s which look like 74HC595s, but include power MOSFETs that can handle up to 250mA. You could easily chain 16 of these together off a set of 3 I/O pins and use one cog per pair of chains for a total of 1024 LEDs and update them well over 1000 times a second from a bitmap in HUB memory. That's fast enough to do PWM control of apparent brightness.

    Bigger issues include power management and signal distribution in the presence of high noise levels (from the LED power switching). Remember that, if you're using ordinary LEDs, you're already talking about possibly switching 20A at KHz rates
  • jazzedjazzed Posts: 11,803
    edited 2010-10-03 10:39
    Jack Buffington wrote: »
    Yes. I've done it. Specifically, I'm controlling 7680 LEDS (2560 RGB LEDs) from a single propeller. One propeller captures video from a VGA source and sends it over a high speed serial line to 40 other propellers, each controlling 64 RGB LEDs. I'll show it off when I am allowed to but for now I'm under a NDA. ...
    This is fantastic :) Can't wait to see the demo. How much power is used? I remember seeing animated LED signs around Taipei Taiwan 20 years ago; now there are a few signs on US101 in the Bay Area. Someone else had a demo ... BTX?
  • Jack BuffingtonJack Buffington Posts: 115
    edited 2010-10-03 18:30
    The LEDs that I used are really small so each 8x8 array only uses just under 2 watts at full brightness when displaying white. Even still, we are finding that it is nice to dim them to about 25% brightness for indoor use under somewhat bright lighting. That brings the wattage down a bit.

    It is looking to be at least six months before I can openly show it off. It kind of stinks that most of my work I can't talk about. That makes things difficult as a freelancer. At least this one I'll eventually be able to show off though. A lot of my stuff I can never talk about...
  • HumanoidoHumanoido Posts: 5,770
    edited 2010-10-04 03:42
    Jack Buffington wrote: »
    It is looking to be at least six months before I can openly show it off. It kind of stinks that most of my work I can't talk about. That makes things difficult as a freelancer. At least this one I'll eventually be able to show off though. A lot of my stuff I can never talk about...
    Never talk about it? Why? Did someone pay you that much money to force you to honor a lifetime NDA? How much money does it take?
  • LeonLeon Posts: 7,620
    edited 2010-10-04 04:17
    NDAs I've signed haven't had a time limit. It's up to the customer to make the details public, not the contractor, as a rule.
  • RaymanRayman Posts: 14,849
    edited 2010-10-04 05:57
    I also have a Prop powered 8x8xRGB matrix driver...

    and, no NDA... Showed it off at UPEW.

    Here's a previous post about it:
    http://forums.parallax.com/showthread.php?t=120181&highlight=matrix
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-10-04 06:49
    Humanoido, you take the job or you don't, that's the money they pay you.

    NDA's can also be used by the little guy if he wants to show his stuff to a company before patenting etc.

    In practise an NDA just means they can sue you if you disclose, if the product is defunct or the business is shut no one is likely to care (sue you).

    Graham
  • AirborneAgainAirborneAgain Posts: 1
    edited 2012-01-05 19:03
    Jack Buffington wrote: »
    Yes. I've done it. Specifically, I'm controlling 7680 LEDS (2560 RGB LEDs) from a single propeller. One propeller captures video from a VGA source and sends it over a high speed serial line to 40 other propellers, each controlling 64 RGB LEDs. I'll show it off when I am allowed to but for now I'm under a NDA. The cool thing is that I have a lot more bandwidth left to control more LEDs. I probably could have controlled about 13,000 RGB LEDs from a single serial line and the prop is capable of capturing a lot more data than that so if another serial line was added then it could really get ridiculous.

    Jack,

    I just found this thread while looking at the feasibility of building my own 72"x192" LED billboard. At 1" spacing, that would put me at around 14000 LEDs. Are you allowed to talk about the project, yet? If so, I would love to get some information about it. To buy a display this size is upwards of $20,000+ USD, but I figure I could build one for closer to a quarter of that price.

    Thanks in advance,

    Doug Anderson
  • lanternfishlanternfish Posts: 366
    edited 2012-01-05 19:47
    Hi Jack
    Jack Buffington wrote: »
    Yes. I've done it. Specifically, I'm controlling 7680 LEDS (2560 RGB LEDs) from a single propeller. One propeller captures video from a VGA source and sends it over a high speed serial line to 40 other propellers, each controlling 64 RGB LEDs. I'll show it off when I am allowed to but for now I'm under a NDA. The cool thing is that I have a lot more bandwidth left to control more LEDs. I probably could have controlled about 13,000 RGB LEDs from a single serial line and the prop is capable of capturing a lot more data than that so if another serial line was added then it could really get ridiculous.

    What resolution is the VGA source (640 x 480, 800 x 600 .... ?). Pity you can't disclose the code as I have been mucking around with VGA capture to RGB with no success yet! Actually VGA capture via frame buffer ($$$) then decimating to smaller resolution.

    Would you breach the NDA if you gave some hints???????

    Cheers
  • ReinhardReinhard Posts: 489
    edited 2012-01-06 05:25
    Hi,
    this a little different issue,
    but I found this
    http://www.objectivej.com/hardware/propcluster/index.html
    and think thats not too far from the thread

    Reinhard
  • VIRANDVIRAND Posts: 656
    edited 2012-01-06 15:12
    To control thousands of LEDs, it makes more sense to use latches or shift registers (like 74HC573 or 74HC595?) than more propellers for the driving pins.
    But a project I did which latched up to 256 LEDs used 5 AMPS just for the LEDs, and over 1000 points to solder.
    If you use matrix displays then the process of raster scanning them all makes them dimmer as the area gets larger and their duty cycle gets smaller.

    edit: to add...
    Smack's LED array seems to be matrix, which I determined by seeing flicker in some of its effects but not others.
    The effect that makes the room look like cubes for example can be done without scanning the matrix but instead leaving on
    some rows and columns.
    And so, if they have , lets say 10,000 LEDs in their matrix, they only need 200 pins (for 100H+100V pixels) to drive it.
  • kwinnkwinn Posts: 8,697
    edited 2012-01-06 17:23
    @lanternfish, 640x480 would require 307,200 rgb leds for color, so effectively you woud be driving 921,600 leds. The 2560 rgb leds would give you a resolution of around 64x40 if you wanted an aspect ratio near the standard 4x3 and maximum use of 8 bit wide driver chips.

    Sorry, misread your post. Thought you meant output resolution.
  • JasonDorieJasonDorie Posts: 1,930
    edited 2012-01-06 17:27
    The TLC5948 LED driver (and others like it) are easy to control, and handle doing the PWM and current control for you, and they can be daisy chained up to a decent length (they don't specify a maximum on their datasheet IIRC). I've gotten one of them (16 channels) to update at ~17KHz (that's 17,000 full cycle updates per second) using two cogs (and it might be possible to do it in one). So, driving 3 discrete chains of them, say 16 chips each, gives you RGB control of 256 LEDS, with lots of pins and both time & cogs left over for master / slave communication.

    That chip is meant for doing large displays, like LED billboards, and can be communicated with at up to 30MHz.
  • RaymanRayman Posts: 14,849
    edited 2012-01-06 17:34
    BTW I've got 6 of the Adafruit 32x16 RGB LED panels working from 1 Prop chip.
    I just calculated that's 9,216 LEDS from 1 Prop...
  • AleAle Posts: 2,363
    edited 2012-01-07 00:50
    Look for BTX's threads from 2007/2008 he did quite an amazing work with many propellers and thousands of LEDs
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