Project:LED Brick Matrix

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Goal

to make a matrix of RGB LEDs with scrolling letters and images in a 6X29 res glass block wall above the storefront.

Glass bricks above windows can be pixelated
see?

Problems

Arduino currently in use has 14 output pins. It is theoretically possible to drive 182 LEDs by using all 14 of them by using charlieplexing, but there are 522 LEDs to drive (6*29*3).

Current plan: Use 29 WS2803D LED Drivers to drive all LEDs individually, with one chip hooked to the LEDs in each column.

Github: http://github.com/redmountainmakers/led_brick/
Uses hardware SPI with 1st WS2803D's SDI pin hooked to Arduino's MOSI, and CLK pin hooked to Arduino's SCK.

Other bits needed:

  • Lots of wire. Size required depends on how much current we run through; each LED can take 30mA for each color, but we won't run it that way for long.
  1 column max current: 540mA
  3 column max current: 1.62A (voltage drop for 5VDC over 8ft (round trip) of 22AWG solid copper wire: 9.5%, heat dissipation: ~0.5W)
  5 column max current: 2.16A (voltage drop for 5VDC over 8ft (round trip) of 18AWG solid copper wire: 4.8%, heat dissipation: ~0.5W)
  Note: Stranded wire of the same gauge will have less voltage drop/heat loss.
  • wire for data/clock/vcc (low power, but needs to run at 2MHz+)
  • wire for LED cathodes, only needs to handle 30mA
  • 29 resistors for current calibration; 1.25kOhm for ~20mA or ~920kOhm for 30mA.
  • Ceramic decoupling capacitor per chip to put between vcc+gnd.

meets

Tuesdays 6:30pm 5502 1st ave n

participants

Resources

  • Hardware Sources
    • ebay
    • http://octopart.com/ -- not helpful for the WS2803
      • (4x) Single Sided Positive Pre-Sensitized PCB (4"" x 6"" x 1/16"") - via Amazon through Jameco Electronics
      • (174x) 4 pin Molex female pin connectors
      • (29x) 3 pin Molex female pin connectors
      • (29x) 2 pin Molex female pin connectors
      • (174x) 4 pin Dupont female pin connectors
      • 100ft 22guage 4 wire alarm system cabling
      • (2x) Smooth-cast 300 casting resin - trial size from Smooth-on.com
      • (1x) Mold-Star 15 platinum catalyst silicone rubber - trial size (for molding LED clips)
      • (1x) 1/16" 24"x24" acrylic sheet
      • (100ft) 50lb test fishing line
      • (400x) 10x24 1 inch bolts/nuts
      • (60x) 1/2" screw eye hooks
      • (10x) 10ft Schedule 40 1" diameter PVC pipe

Cost

$35 ws2803D $40 200 LEDS $30 arduino $.0005 29 1.25 kiliaohms 5v Power supply decoupling capacitors $20 Chicken Wire $10 18 gauge wire 50 ft $32 (4x) Photosensitive PCB blanks (8 finished circuit boards per 4"x6" PCB) $12 Ferric Chloride etchant $12 Positive Developer