Visualizing LEDs For More Efficient Pin Packing

June 19, 2019 by Kerry Scharfglass 1 Comment

The archetypal “blink an LED” is a great starter project on any platform, but once the bug takes hold that quickly turns into an exploration of exactly how many LEDs a given microcontroller can drive. And that often leads to Charlieplexing. A quick search yields many copies of The Table describing how many LEDs can be driven by a given number of pins but that’s just the most rudimentary way to describe it. Way back in 2013 [M Rule] developed a clever trick to describe the number of LED matrices which can be driven by a Charlieplexed array of a given size that makes this process much more intuitive. The post may be old, but we promise the method is still fresh.

[M Rule] was specifically looking to drive those big, cheap single color LED matrices which are often used to make scrolling signs and the like. These parts are typically a matrix of LEDs with a row of common cathodes and one of common anodes. Internally they are completely dumb and can be driven by row/column scanning, or any other way a typical matrix can be controlled. The question is, given known matrix sizes, how many can be driven with a a number of Charlieplexed LED drive pins?

The first step is to visualize the 1D array of available pins as a 2D matrix, as seen to the right. Note each numbered pin is the same on the X and Y, thus the black exclusion zone of illegal drive pin combinations slicing across the graph (you can’t drive an LED connected to one pin twice). The trick, if one were to say it resides in a single place, would be titling the axis anode and cathode, representing two “orientations” the drive pins can be put in. With this diagram [M Rule] observed you can simply drop a matrix into the array. If it fits outside the exclusion zone, it can be driven by those pins!

To the left is what this looks like with two 8×8 matrices, one connected between pins 1-8 and 9-16, the other connected between 9-16 and 1-8. This isn’t terribly interesting, but the technique works just as well with single LEDs and any size matrix, including 7-segment displays. Plus as long as an element doesn’t overlap itself it can wrap around the edges leading to some wild visuals, like 14 RGB LEDs on seven pins to the right.

The most extreme examples are pretty exotic. Check out [M Rule]’s post for the crown jewel; 18 pins to drive six 5×7 modules, six 7-segment displays, 12 single LEDs, and 18 buttons!

If this color coded diagram seems familiar, you may be remembering [openmusiclabs]’ excellent diagram describing ways to scan many of buttons. Or our coverage of another trick of matrix topology by [M Rule] from a few weeks ago.

IKEA Cloud Lamp Displays The Weather With An ESP8266

June 12, 2019 by Tom Nardi 5 Comments

The IKEA DRÖMSYN is a wall mounted cloud night light that’s perfect for a kid’s room. For $10 USD, it’s just begging for somebody to cram some electronics in there and make it do something cool. Luckily for us, [Jodgson] decided to take on the challenge and turned this once simple lamp into a clever weather display. It even still works as an LED lamp, if you’re into that sort of thing.

After stripping out the original hardware, [Jodgson] installed a Wemos D1 Mini and a string of fourteen SK6812 RGB LEDs that run down the length of the cloud’s internal structure. Weather data is pulled down with the OpenWeatherMap API, and conditions are displayed through various lighting colors and effects.

Sunny days are represented with a nice yellow glow, and a cloudy forecast looks like…well it’s already a white cloud so that one’s pretty easy. If rain is expected the cloud turns blue and the bottom LEDs flicker a bit to represent raindrops. When there’s a thunderstorm, the cloud will intermittently flash random LEDs on the strip a bit brighter than their peers; a really slick effect that gets the point across immediately.

This isn’t the first time we’ve seen somebody take a cheap light from IKEA and turn it into something much more impressive with the ESP8266. Just like with that previous project, we wouldn’t be surprised to see this particular modification popping up more in the future.

New PCB Revives Ancient Bubble LED Displays

June 11, 2019 by Ted Yapo 14 Comments

For those of us who remember LED calculators, the HP 5082-7400 series red “bubble” displays hold a special charm. Available in 3, 4, or 5-digit varieties, these multiplexed 7-segment displays provided countless hours of entertainment to those who would spell upside-down words on their pocket calculators. In case you happen to be lucky enough to have access to a few of these beautiful vintage display sticks, [Gigawipf] has designed a small driver PCB that lets you easily interface them to a modern microcontroller.

At the heart of the board, aimed at either the 5082-7405 or 5082-7415 5-digit modules, are a pair of 74HC595 shift registers in tiny QFN packages. Five lines from one register drive one of the common cathodes for the selected digit, while the other register drives the eight anode lines through 330-Ohm resistors. The boards are slightly smaller than the width of the displays allowing you to stack them seamlessly for more digits, and eight header pins on each allow you to plug them into solderless breadboards for prototyping. The result is easy to drive with some simple code, and [Gigawipf] provides an example for Arduino as part of the project. The Eagle design files are supplied, as well as Gerbers for those who just want to have some boards made. This sounds like a great way to get some of these vintage displays going again.

If you can’t find any of these displays to play, with, you can try making some larger digits from individual surface-mount LEDs.

Simple Trick For LEDs On Solderless Breadboards

June 9, 2019 by Ted Yapo 39 Comments

Sometimes the most useful hacks are also the simplest ones. A case in point is the LED and resistor assembly that [Skippy] recently posted on his blog. The idea is to solder up some pre-made indicators with integrated resistors to save space on the breadboard when prototyping — instead of four slots, you only use two per LED. This is about as easy a trick as you can imagine, but it has the hallmark of a classic hack: a high utility-to-work ratio.

The deluxe assembly uses a two-pin header as a base to plug into the breadboard. This, of course, could be optional since some breadboards have a memory for the widest pin previously inserted — using header pins may eventually make the slots a little flaky for smaller component leads. But, if you’re mostly using header pins in the breadboard anyway, this is a good way to avoid kinking the leads.

While there are LEDs available with integrated dropping resistors, building your own means you can use whatever LEDs you prefer — or simply have on hand — and adjust the resistor value for different voltages or to adjust the brightness. And for those of you who plug in LEDs without current-limiting resistors, we’re going to assume that you’ve thoroughly researched whatever is driving them and done the math to ensure they’re safe. Or not: they’re your LEDs after all.

We previously featured a no-solder breadboarding trick for SMD LEDs. What’s your favorite solderless breadboard hack? Let us know in the comments below.

Thanks to [Roboteernat] for the tip!

Animated Pixel Lamp Is A Must For Any Chiptuner’s Bedroom

June 2, 2019 by Lewin Day 5 Comments

Lamps are quite often simple things, designed to light an area and perhaps add a touch of style to a room. Of course, it’s 2019 now, and we don’t need to settle for just that. We can have wildly colored animated lamps if we want to! (French Youtube link, embedded below.)

The lamp in question is the work of [Heliox], who knows her way around an LED or two (hundred). In this build, a string of WS2812 addressable RGB LEDs are hooked up to an Arduino Mega brain. The LEDs are fitted into a round lamp body, with a rectangular diffuser for each one. This creates an attractive pixellated effect and gives the animations a charming 8-bit quality. A thin outer shell is 3D printed in white plastic to further diffuse the light. The top of the lamp rotates an internal potentiometer to control mode selection. There’s also a brightness knob on the bottom if things get a touch too intense.

It’s a tidy build that uses 3D printing and addressable LEDs to quickly and easily create a lamp with a fun retro aesthetic. We could imagine this making a great piece for a hip sitcom apartment. We fully expect to see similar lamps on sale in the next couple of years. Video after the break.

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Make Your Own Old School LED Displays

May 31, 2019 by Lewin Day 13 Comments

We live in an era in which all manner of displays are cheap and readily available. A few dollars spent online can net you a two-line alphanumeric LCD, a graphical OLED screen, or all manner of other options. Years ago however, people made do with little monolithic LED devices. [sjm4306] wanted to recreate something similar, and got down to work (Youtube link, embedded below).

The resulting device uses 0603 sized SMD LEDs, soldered onto a tiny PCB. 20 LEDs are used per digit, which can display numbers 0-9 and letters A-F. The LEDs are laid out in a pattern similar to Hewlett-Packard designs from years past. This layout gives the numerals a more pleasant appearance compared to a more-classic 7-segment design. Several tricks are used to make the devices as compact as possible, such as putting vias in the LED pads. This is normally a poor design technique, but it helps save valuable space.

[sjm4306] has developed a breadboard model, and a more advanced version that has a pad on the rear to mount a PIC16F88 microcontroller directly. We look forward to seeing these modules developed further, and can imagine they’d prove useful in a variety of projects.

For reference, check out these Soviet-era 7-segment displays. Video after the break.

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A Work Light For Hacker Events

May 31, 2019 by Jenny List No comments

If you’ve ever attended a hacker camp, you’ll know the problem of a field of tents lit only by the glow of laser illumination through the haze and set to the distant thump of electronic dance music. You need to complete that project, but the sun’s gone down and you didn’t have space in your pack to bring a floodlight.

In Days of Yore you might have stuck a flickering candle in an empty Club-Mate bottle and carried on, but this is the 21st century. [Jana Marie] has the solution for you, and instead of a candle, her Club-Mate bottle is topped a stack of LED-adorned PCBs with a lithium-ion battery providing a high intensity downlight. It’s more than just a simple light though, it features variable brightness and colour temperature through touch controls on the top surface, as well as the ability to charge extra 18650 cells. At its heart is an STM32F334 microcontroller with a nifty use of its onboard timer to drive a boost converter, and power input is via USB-C.

We first saw an early take on this project providing illumination for a bit of after-dark Hacky Racer fettling at last year’s EMF 2018 hacker camp, since then it has seen some revisions. It’s all open-source so you can give it a go yourself if you like it.