The Possibility Of Driving 16,000 RGB LEDs

Like just about everyone we know, [Luis] decided a gigantic RGB LED matrix would be a cool thing to build. Gigantic LED matrices are very hard to build, though: not only do you have to deal with large power requirements and the inevitable problems of overheating, you also need to drive a boat load of LEDs. This is not easy.

[Luis] found a solution to the problem of driving these LEDs with a new, fancy ARM Cortex M4 microcontroller. All Cortex M4 ARMs have DMA, making automatic memory transfers to peripherals and LED strips a breeze.

The microcontroler [Luis] is using only supports 1024 transfers per transfer set, equating to a maximum of 14 LEDs per transfer. This problem can be fixed by using the ping-pong mode in the DMA controller by switching between data structures for every DMA request. Basically, he’s extending the number of LEDs is just switching between two regions of memory and setting up the DMA transfer.

The result is much better than [Luis]’ original circuit that was just a bunch of SPI lines. It also looks really good, judging by the video below. It’s not quite a gigantic LED matrix yet, but if you want to see what that would look like, check out the huge 6 by 4 foot matrix hanging in the Hackaday overlord office.

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A Hacker-Friendly Blinky USB Stick

The availability of Smart RGB LED’s, either as individual units, as strips or even as panels, have made blinky light projects with all kinds of color control and transition effects easy to implement using even the simplest of controllers. Libraries that allow control of these smart LEDs (or Smart Pixels as they are sometimes called)  make software development relatively easy.

[overflo] at the Metalab hackerspace in Vienna, Austria recently completed development of usblinky – a hacker friendly blinky USB stick. It can control up to 150 WS2812B smart LED’s when powered via an external power supply, or up to 20 LED’s when powered via a computer USB port. The micro-controller is an ATTiny85 running the Micronucleus bootloader which implements software USB using vUSB. The hardware is based on the DigiSpark platform. The usblinky software sources are available on their Github repo. The section on pitfalls and lessons learned makes for interesting reading.

Metalab plans to run workshops around this little device to get kids into programming, as it is easy enough and gives quick visual feedback to get you started. To round off the whole project, [overflo] used OpenSCAD to design a customizable, 3D printable “parametric orb” which can house the LED strip and make a nice enclosure or psychedelic night light. Check out the mesmerizing video of the usblinky Orb after the break.

Thanks to [papst] for sending in this tip.

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LED Matrix Infinity Mirror

[Evan] wrote in to let us know about the LED matrix infinity mirror he’s been working on. [Evan] built a sizable LED matrix out of WS2812B LEDs and mounted them to a semi-reflective acrylic sheet, which makes a pretty awesome infinity mirror effect.

Instead of buying pre-wired strands of serial LEDs like we’ve seen in some other projects, [Evan] purchased individual WS2812 LEDs in bulk. Since the LEDs just had bare leads, [Evan] had to solder wires between each of his 169 LEDs (with some help from a few friends). After soldering up hundreds of wires, [Evan] drilled out holes for each LED in a piece of semi-reflective acrylic and inserted an LED into each hole.

To create the infinity mirror effect, [Evan] mounted the LED matrix behind a window. [Evan] put some one-way mirror film on the outside of the window, which works with the semi-reflective acrylic to create the infinity mirror effect. The LEDs are driven by an Arduino, which is controlled by a couple of free programs to show a live EQ of [Evan]’s music along with patterns and other effects.

The Most Minimal WS2812B Driver

Whether you call them individually controllable RGB LEDs, WS2812, or NeoPixels, there’s no denying they are extremely popular and a staple of every glowey and blinkey project. Fresh off the reel, they’re nearly useless – you need a controller, and that has led to many people coming up with many different solutions to the same problem. Here’s another solution, notable because it’s the most minimal WS2812 driver we’ve ever seen.

The critical component in this build is NXP’s LPC810, an ARM Cortex M0+ in an 8-pin DIP package. Yes, it’s the only ARM in a DIP-8, but still able to run at 30MHz, and hold a 4kB program.

JeeLabs is using the SPI bus on the LPC810 to clock out data at the rate required by the LEDs. The only hardware required is a small LED to drop the voltage from 5V to 3.3V and a decoupling capacitor. Yes, you could easily get away with this as a one-component build.

The build consists of a ring of sixty WS2812b RGB LEDs, and the chip dutifully clocking out bits at the correct rate. It’s the perfect start to an LED clock project, an Iron Man arc reactor (are we still doing those?), or just random blinkey LEDs stuffed into a wearable.

Thanks [Martyn] for sending this one in.

MicroDMA and LEDs

[Jordan] has been playing around with WS2812b RGB LED strips with TI’s Tiva and Stellaris Launchpads. He’s been using the SPI lines to drive data to the LED strip, but this method means the processor is spending a lot of time grabbing data from a memory location and shuffling it out the SPI output register. It’s a great opportunity to learn about the μDMA available on these chips, and to write a library that uses DMA to control larger numbers of LEDs than a SPI peripheral could handle with a naive bit of code.

DMA is a powerful tool – instead of wasting processor cycles on moving bits back and forth between memory and a peripheral, the DMA controller does the same thing all by its lonesome, freeing up the CPU to do real work. TI’s Tiva C series and Stellaris LaunchPads have a μDMA controller with 32 channels, each of which has four unique hardware peripherals it can interact with or used for DMA transfer.

[Jordan] wrote a simple library that can be used to control a chain of WS2812b LEDs using the SPI peripheral. It’s much faster than transferring bits to the SPI peripheral with the CPU, and updating the frames for the LED strip are easier; new frames of a LED animation can be called from the main loop, or the DMA can just start again, without wasting precious CPU cycles updating some LEDs.

IcosaLEDron: A 20-Sided Light Up Ball

Tired of balls that are just balls, and not glowing geometric constructions of electronics and wonderment? Get yourself an IcosaLEDron, the latest in Platonic solids loaded up with RGB LEDs.

The folks at Afrit Labs wanted a fun, glowy device that would show off the capabilities of IMUs and MEMS accelerometers. They came up with a ball with a circuit board inside and twenty WS2812B RGB LEDs studded around its circumference

The frame of the ball is simply a set of twenty tessellated triangles that can be folded up during assembly. The outer shell of the ball is again printed in one piece, but fabricated out of transparent NinjaFlex, an extraordinarily odd, squishy, and likely indestructible material.

Inside the IcosaLEDron is a PCB loaded up with an ATMega328p, an accelerometer, a LiPo battery charger, and quite a bit of wiring. Once the ball is assembled and locked down, the squishy outer exterior is installed and turned into a throwable plaything.

If 20 sides and 20 LEDs aren’t enough, how about a an astonishing 386-LED ball that’s animated and knows its orientation? That’s a project from Null Space Labs, and looking at it in person is hypnotic.

via Makezine

Driving WS2812B Pixels, With DMA Based SPI

Typically bit-banging an I/O line is the common method of driving the WS2812B (WS2811) RGB LEDs. However, this ties up precious microcontroller cycles while it waits around to flip a bit. A less processor intensive method is to use one of the built-in Serial Peripheral Interface (SPI) modules. This is done using specially crafted data and baud rate settings, that when shifted out over the Serial Data Out (SDO) pin, recreate the needed WS2812B signal timing. Even when running in SPI mode, your hardware TX buffer size will limit how many pixels you can update without CPU intervention.

[Henrik] gets around this limitation by using peripheral DMA (Direct Memory Access) to the SPI module in the Microchip PIC32MX250F128B microcontroller. Once properly configured, the DMA controller will auto increment through the defined section of DMA RAM, sending the pixel data over to the SPI module. Since the DMA controller takes care of the transfer, the micro is free to do other things. This makes all of DMA memory your display buffer. And leaves plenty of precious microcontroller cycles available to calculate what patterns you want the RGB LEDs to display.

Source code is available at the above link for those who would like to peruse, or try it out. This is part of [Henrik’s] Pixel Art Project. Video of DMA based SPI pixels after the break:

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