Big RGB LED Cube You Can Build Too

LED cubes are really nothing new, many of us consider the building of a good sized one almost an electronics rite of passage that not so many manage to find the time or have the skill to pull off. It's our pleasure to draw your attention to a lovely build, showing all the processes involved, the problems and the solutions found along the way.

Building a small cube is somewhat of a trivial affair, especially without considering PWM colour mixing, however as simple maths will illustrate, as you increase the number of LEDs on each side, the total number will quickly get quite large. More LEDs need more power and increase control complexity considerably. A larger matrix like this 16 x 16 x 16 LED build, has a total of 4096. This would be a nightmare to drive with plain RGB LEDs, even with cunning multiplexing, but luckily you can buy indexable LEDs in a through-hole package similar to the ubiquitous WS2812-based SMT LEDs you see around. These are based on the PD9823 controller, which can be programmed as if they were a WS2812, at least according to this analysis. Now you can simply chain a column of LEDs, with the control signal passed from LED to nearest neighbour.

Early on in the video build log, you will note there are four power supply modules needed to feed this juice. If we assume each LED consumes 60 mA on full-white (the data for this product link shows a peak value of 100 mA) that is still a total of 246 A or around 1 kW of power. The video does shows a peak power measurement of around this figure, for the whole array on full white, so the maths seems about right.

Control is via a Teensy 4.0 using the FlexIO function of the IMXRT1060RM CPU, and a bunch of 74AHCT595 shift registers giving 32 channels of up to 1000 LEDs per channel if needed. Roughly speaking, using the DMA with FlexIO, the Teensy can drive up to 1 Million LED updates per second, which works out about 32 channels of 100 LEDs per channel updated at 330 frames/sec, so plenty of resource is available. All this is with almost no CPU intervention, freeing that up for handling the 2.4-inch LCD based UI and running the animations, which looks pretty darn slick if you ask us. You can checkout the description of the firmware in the firmware section of the GitHub project. 3D printed jigs allowed for bending and clipping the LEDs leads as well as fixing and aligning the LED column units, so there really is enough detail there to allow anyone so inclined reproduce this, so long as you can swallow the cost of all those LEDs.

For a different approach to LED cubes, checkout this sweet panel based approach, and here's a really small 4x4x4 module for those with less space to spare.

Thanks [Keith] for the tip!

#ledhacks #ledcube #pd9823 #rgb #teensy40

Foam F-35 Learns to Hover

With cheap RC hardware, powerful motors, and high-capacity battery packs, getting something to fly has never been easier. It also helps that, whether you're into fixed-wing craft or multirotors, there's plenty of information and prior art floating around online that you can use to jumpstart your own build. But when it comes to homebrew vertical take-off and landing (VTOL) planes, things are a bit trickier.

Luckily for us, [Nicholas Rehm] has made all the plans and information necessary to duplicate his incredible RC F-35 available for anyone who wants to experiment with these relatively niche fliers. Even if it was a standard park flier, the build would be worth a close look thanks to the vectored thrust motors that give it phenomenal maneuverability and a top speed in the neighboorhood of 120 KPH (80 MPH). But with the flick of a switch, the plane transitions into a tricopter-like flight mode that allows it to land and takeoff vertically.

How does it work? The downward facing motor just behind the "cockpit" lifts up the front of the foam flier and tilts left and right to provide yaw control, while the two motors on the back tilt down to lift up the rear of the aircraft. Aviation buffs in the audience may recognize this as being fairly close to how the actual F-35B hovers, although on the real jet fighter, downward thrust under the wings is generated by redirected turbine exhaust rather than dedicated motors, and yaw control is provided by swiveling the engine's nozzle rather than the front lift fan.

Getting the plane to takeoff vertically was one thing, but being able to transition from a hover into forward flight was quite another. To make this aerial transformation possible [Nicholas] actually had to write his own flight controller software, which he calls dRehmFlight. The GPLv3 code runs on the Teensy 4.0 and uses the common GY-521 MPU6050 gyroscope/accelerometer, so you don't need to get any custom boards spun up just to give it a test ~~drive~~ flight. In the video below he walks through configuring the software for VTOL operation by defining how each control surface and motor is to respond to control input given the currently selected flight mode.

It probably won't surprise you to hear that this isn't the first time [Nicholas] has experimented with unusual flying machines. Last year we covered his RC Starship, which managed to stick the "belly flop" landing even before SpaceX managed to get the real life version down in one piece.

#toyhacks #dollartreefoam #f35 #flightcontroller #foam #hover #teensy40 #vtol

MIT’s Knitted Keyboard is Quite a Flexible MIDI Controller

There are only so many ways to make noise on standard instruments such as acoustic pianos. Their rigidity and inputs just don't allow for a super-wide range of expression. On the other hand, if you knit your interface together, the possibilities are nearly endless. MIT's new and improved knitted keyboard is an instrument like none other -- it responds to touch, pressure, and continuous proximity, meaning that you can play it like a keyboard, a theremin, and something that is somewhere in between the two. Because it's a MIDI interface, it can ultimately sound like any instrument you've got available in software.

The silver keys of this five-octave interface are made of conductive yarn, and the blue background is regular polyester yarn. Underneath that is a conductive knit layer to complete the key circuits, and a piezo-resistive knit layer that responds to pressure and stretch. It runs on a Teensy 4.0 and uses five MPR121 proximity/touch controllers, one per octave.

The really exciting thing about this keyboard is its musical (and physical) versatility. As you might expect, the keyboard takes discrete inputs from keystrokes, but it also takes continuous input from hovering and waving via the proximity sensors, and goes even further by taking physical input from squeezing, pulling, stretching, and twisting the conductive yarns that make up the keys. This means it takes aftertouch (pressure applied after initial contact) into account -- something that isn't possible with most regular instruments. And since this keyboard is mostly yarn and fabric, you can roll it up and take it anywhere, or wrap it around your neck for a varied soundscape.

If you're looking for more detail, check out the paper for the previous version (PDF), which also used thermochromic yarn to show different colors for various modes of play using a heating element. With the new version, [Irmandy Wicaksono] and team sought to improve the sensing modalities, knitted aesthetics, and the overall tactility of the keyboard. We love both versions! Be sure to check it out after the break.

Want to play around with capacitive touch sensors without leaving the house for parts? Make your own from paper and aluminum foil.

#musicalhacks #aftertouch #capacitivetouch #midicontroller #mpr121 #teensy #teensy40