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Random LED Dots: Hardware Layout

Quite some time ago, Sophi gave me a common-anode RGB LED panel and told me to make something of it. In a spate of desk-clearing, I hammered out a quick-and-dirty multiplexed display from found materials: 2N2907 transistors as row source drivers and 74HC595 shift registers abused as column sink drivers, plus the obligatory Arduino Pro Mini and 3D printed holder:

Random LED Dots - circuit board

Random LED Dots – circuit board

A sheet of milk-white acrylic diffuses the glittery LED dots into pastel disks. I think it might look better without the diffuser; it certainly has a harder-edged tech look:

Random LED Dots - overview - no diffuser

Random LED Dots – overview – no diffuser

A neutral-density filter would boost the contrast without hiding any of the details.

It obviously needs an enclosure, but, around here, that’s in the nature of fine tuning.

The transistors and shift registers  cower under the panel:

Random LED Dots - circuit layout - top

Random LED Dots – circuit layout – top

The bottom view exposes the hand wiring, plus the slot required to adapt the LED panel’s non-100-mil layout to the protoboard’s holes. I chopped out the slot with a Dremel saw, attached socket strips to the panel, and epoxied the floating strip in place:

Random LED Dots - circuit layout - bottom

Random LED Dots – circuit layout – bottom

The prospect of wiring 32 discrete resistors filled me with dread, so I just tombstoned SMD resistors onto the protoboard solder blobs:

Random LED Dots - circuit layout - RB SMD resistors

Random LED Dots – circuit layout – RB SMD resistors

The slot required slightly longer bridge wires:

Random LED Dots - circuit layout - G SMD resistors

Random LED Dots – circuit layout – G SMD resistors

The layout, such as it is, made those short, direct wires possible. A PCB with SMD chips would be even better.

More on the circuitry tomorrow…

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  1. #1 by madbodger on 2015-05-18 - 09:20

    I too have become tired of those resistors, and am becoming fond of dedicated current regulating LED driver/multiplexer chips like the MAX7221. They’re kind of spendy, but save time and room, which is often worth it to me.

    • #2 by Ed on 2015-05-18 - 10:36

      Aye!

      I have some TLC5916 drivers left over from the Totally Featureless Clock, but this one called for utterly trivial hardware, even though it requires more hand-soldering. That’s my story and I’m sticking with it!

      The TLC5971 has 4×3 PWM channels, so (I think) a pair of them would suffice for per-dot brightness control. Cheap, too; I should pick up a few just to have around…

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