Addressable LEDs From A Z80

January 19, 2023 by Jenny List 3 Comments

If you buy WS2812s under the Adafruit NeoPixel brand, you’ll receive the advice that “An 8 MHz processor” is required to drive them. “Challenge Accepted!“, says [ShielaDixon], and proceeded to first drive a set from the 7.3 MHz Z80 in an RC2014 retrocomputer, and then repeat the feat from a 3.5 MHz Sinclair ZX Spectrum.

The demos in the videos below the break are all programmed in BASIC, but she quickly reveals that they call a Z80 assembler library which does all the heavy lifting. There’s no microcontroller behind the scenes, save for some glue logic for address decoding, the Z80 is doing all the work. They’re all implemented on a pair of RC2014 extension cards, a bus that has become something of a standard for this type of retrocomputer project.

So the ubiquitous LEDs can be addressed from some surprisingly low-powered silicon, showing that while it might be long in the tooth the Z80 can still do things alongside the new kids. For those of us who had the Sinclair machines back in the day it’s particularly pleasing to see boundaries still being pushed at, as for example in when a Z80 was (almost) persuaded to have a protected mode.

Continue reading “Addressable LEDs From A Z80” →

LED Driver Circuit For Safety Hat Sucks Single AAA Cell Dry

January 19, 2023 by Donald Papp 21 Comments

[Petteri Aimonen] created an omnidirectional LED safety light to cling to his child’s winter hat in an effort to increase visibility during the dark winter months, but the design is also great example of how to use the Microchip MCP1640 — a regulated DC-DC step-up power supply that can run the LEDs off a single AAA cell. The chip also provides a few neat tricks, like single-button on/off functionality that fully disconnects the load, consuming only 1 µA in standby.

[Petteri]’s design delivers 3 mA to each of eight surface-mount LEDs (which he says is actually a bit too bright) for a total of about 20 hours from one alkaline AAA cell. The single-layer PCB is encased in a clear acrylic and polycarbonate enclosure to resist moisture. A transistor and a few passives allow a SPST switch to act as an on/off switch: a short press turns the unit on, and a long press of about a second turns it back off.

One side effect is that the “off” functionality will no longer work once the AAA cell drained too badly, but [Petteri] optimistically points out that this could be considered a feature: when the unit can no longer be turned off, it’s time to replace the battery!

The usual way to suck a battery dry is to use a Joule Thief, and while this design also lights LEDs, it offers more features and could be adapted for other uses easily. Interested? [Petteri] offers the schematic, KiCAD file for the PCB, and SVG drawing of the enclosure for download near the bottom of the project page.

Illuminated smart curtain in front of a window, beside a Christmas tree

Smart LED Curtain Brings Sprites To Your Windows

January 14, 2023 by Dave Walker 13 Comments

Mobile interface for LED smart curtain display — A mobile interface is a nice touch

Anybody who has ever seen a video wall (and who hasn’t?) will be familiar with the idea of making large-scale illuminated images from individual coloured lights. But how many of us have gone the extra mile and fitted such a display in our own homes? [vcch] has done just that with his Deluxe Smart Curtain that can be controlled with a phone or laptop.

The display itself is made up of a series of Neopixel strips, hung in vertical lines in front of the window. There is a wide gap between each strip, lending a ghostly translucent look to the images and allowing the primary purpose of the window to remain intact.

The brains of the system are hosted on a low-cost M5stack atom ESP32 device. The data lines for the LEDs are wired in a zig-zag up and down pattern from left to right, which the driver software maps to the rectangular images. However, the 5V power is applied to the strips in parallel to avoid voltage drops along the chain.

If you’d like to build your own smart curtain, Arduino sketch files and PHP for the mobile interface are included on the project page. Be sure to check out the brief video of what the neighbors will enjoy at night after the break.

If video walls are your kind of thing, then how about this one that uses Ping Pong Balls as diffusers? Continue reading “Smart LED Curtain Brings Sprites To Your Windows” →

IoT Archaeology Leads To API Resurrection

January 9, 2023 by Jenny List 21 Comments

What happens when someone’s personal project is turned into a startup which becomes something of a publicity darling, then collapses with very little product shipped and takes all its customers’ money with it?

That’s the subject of a blog post from [Kevin Chung], who investigated the legacy of NYCTrainSign, a company whose product was an LED NYC subway sign and which has become a meme byword for a startup scam. Along the way he found himself reverse engineering its API, and eventually even purchasing the expired domain name to resurrect the API for any NYCTrainSigns that may still be out there.

Securing a second-hand NYCTrainSign, he dismantled it to see what made it tick. Inside the handmade wooden case was an array of LED panels, driven by a Raspberry Pi 3 and an Adafruit LED panel HAT. This gave pause for thought, as the component choice gives rise to a very high BoM cost which was unsustainable given their habit of steep discounts.

The software proves straightforward enough to reverse engineer, and since the original domain was for sale he bought it and set up a replacement API. Do you have one of the few signs that made it to customers? Now you can run it again.

The rest of the piece tells a tale that will be familiar to startup veterans: one of far too much marketing, too many bosses, and too little engineering to create a viable product. The founders remain tight-lipped about what happened and where the money went, but since there are few more efficient money pits than a badly-run startup, it’s more likely that ill-advised spending is to blame than someone running off with suitcases of cash.

If you’d like a public transit sign without the dodgy start-up, we’ve got you covered.

LEDCard: The Pocketable Ring Light

January 1, 2023 by Maya Posch 17 Comments

How many times have you found yourself fumbling about with lighting while trying to get a clear up-close shot of an object? Although smartphones come with pretty nice cameras these days, properly lighting an object and taking impressive macro shots isn’t exactly their strong suit. This is where [MisterHW]’s LEDCard is a very welcome companion. Not only does it provide a credit card sized ring light, it also allows for a molded acrylic lens to be inserted for high-quality macro shots.

The project in its current iteration consists out of a single PCB with rechargeable Li-ion coin cells (LIR2430) and a USB-powered charge controller. After charging the LEDCard (or inserting freshly charged Li-ion coin cells), a single button press will light up the SMD LEDs via the LM3410 LED driver IC. Press the ON button gently (half-press) for medium brightness and fully for full intensity. Finally, pressing the TEST button with the LEDs lit performs a battery level test that turns the LEDs off if the battery is ok. If they stay lit, it’s time to recharge the LEDCard.

As [MisterHW] points out, the LEDCard being compact enough to carry around with you wherever you go makes it suitable as an emergency flashlight as well. It’s also not the final iteration of the design. Future (incremental) improvements include a diffuser for the ring light and more. Even so, in its current state LEDCard is already a proven design.

Spinning Holographic POV Christmas Tree Of Death

December 27, 2022 by Joseph Long 11 Comments

[Sean Hodgins] really harnessed the holiday spirit to create his very own Giant Spinning Holographic Christmas Tree (of Death). It’s a three-dimensional persistence-of-vision (POV) masterpiece, but as a collection of rapidly spinning metal elements, it’s potentially quite dangerous as well. As [Sean] demonstrates, the system can display other images and animations well beyond the realm of mere holiday trees.

Initial experiments focused on refining the mechanical structure, bearings, and motor. A 1/2 horsepower A.C. motor was selected and then the dimensions of the tree were “trimmed” to optimize a triangular frame that could be rotated at the necessary POV speed by the beefy motor. A six-wire electrical slip ring allows power and control signaling to be coupled to the tree through its spinning central shaft.

The RGB elements are SK9888 LEDs also know as DotStar LEDs. DotStar LEDs are series-chainable, individually-addressable RGB LEDs similar to NeoPixels. However, with around 50 times the pulse width modulation (PWM) rate, DotStars are more suitable for POV applications than NeoPixels. The LED chain is driven by a Raspberry Pi 4 single board computer using a clever system for storing image frames.

If deadly rotational velocity is not your cup of tea, consider this slower spinning RGB Christmas tree featuring a DIY slip ring. Or for more POV, may we suggest this minimalist persistence-of-vision display requiring only a few LEDs and an ATtiny CPU.

Continue reading “Spinning Holographic POV Christmas Tree Of Death” →

3D Printed Light Pipe Turns Overly-Bright LED Into Design Harmony

December 22, 2022 by Donald Papp 14 Comments

There are a number of ways to efficiently and elegantly limit an LED’s brightness, but [Tommy] found that using a light pipe or diffuser can integrate better with a device, especially when the device itself is mostly 3D printed in the first place.

Infill has an effect on appearance. 20% infill on the left, 100% infill on the right.

For some problems the Goldilocks approach is the way to go. [Tommy] designed a small array of different LED cover options, and tested each to see what yielded the best results for his printed kit. Some of the biggest takeaways include:

100% infill is best for even results (although interesting shadows happen at less than 100% infill.)
Interesting things happen with 7 to 11 mm of top layers of clear PLA, when illuminated from below with a 5 mm high-brightness LED. An even diffusion of light starts to give way to a circular gradient as the upper layer gets thicker.
LEDs emit their light mainly upward in a round pattern. Corners will always be darker, even more so if the guide is not round. This effect becomes noticeably more pronounced as the light guide grows in size, putting a practical upper limit on its effective dimensions.

[Tommy] explores these kinds of issues because he designs and builds electronic synth instruments, and they are mostly 3D printed. He explores efficiency and is always happy to share his findings about what works and doesn’t work.

Of course, the usual ways to deal with an overly-bright LED are to limit its current or control its brightness by driving it with a PWM signal. The right approach depends on the application and the scale of the design, and there are actually quite a few ways to crack this nut. Luckily, our own [Inderpreet Singh] is here to tell you all about how best to control LED brightness.