Tag Archives: LEDs

Open Source Pumpkin PCB

The Great Pumpkin PCB on a pumpkin!

Eric over at Low Voltage Labs has posted up his design for a simple PCB ideal for putting an LED into a pumpkin. This is very much like our simple LED pumpkin project but in a neat, reusable format. And it makes a mighty cute little jack-o-lantern all on its own.

KiCAD - pumpkin PCB layout

He has made it available as a kit with PCB, switch, resistor, battery holder and the same candle flicker LEDs which we love so much. Unfortunately, the kit is currently sold out. Hopefully he’ll make more, if not in time for this Halloween, then at least for next year.

From the mailbag: flickering LEDs in series

We recently got a question about our flickering LEDs:

I’m wondering if it’s possible to wire these in series?

It’s a good (and not entirely uncommon) question, and the short answer is: “Yes, but not with each other.”

These LEDs have a little chip inside that turns them on and off in a flickering pattern. You can see it in the photo of the flat-topped white LED above. On the upper pad is the yellowish phosphor over the LED die. On the lower pad is the chip that turns the LED on and off.

If you put two of these in series, the first one turns the next one on and off repeatedly, interrupting the second chip and preventing it from executing its flickering pattern. The result is that you get momentary blinking, but not the nice flickering pattern.  (So yes, both would in fact light up; they just don’t behave how you might hope that they would.)

So how can you hook up a bunch of flickering LEDs together? If you want each LED to flicker separately, you can hook them up in parallel. But there is a way to use these in series with other LEDs. We can even use this to combine multiple LED colors to create some fantastic LED “flames” that would be great for stage props or putting inside pumpkins.
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Basics: Picking Resistors for LEDs

5 mm warm white diffused LED

So… you just want to light up an LED. What resistor should you use?

Maybe you know the answer, or maybe everyone already assumes that you should know how to get to the answer.  And in any case, it’s a question that tends to generate more questions before you actually can get an answer: What kind of LED are you using? What power supply? Battery? Plug-in? Part of a larger circuit? Series? Parallel?

Playing with LEDs is supposed to be fun, and figuring out the answers to these questions is actually part of the fun.  There’s a simple formula that you use for figuring it out, Ohm’s Law. That formula is V = I × R, where V is the voltage, I is the current, and R is the resistance. But how do you know what numbers to plug into that formula to get out the right resistor value?

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Prefabricated Octolively Modules

Octolively Modules

Last year we released Octolively, an open source interactive LED kit, designed to respond in gentle and complex ways to stimulus provided by human interaction.

While Octolively has been a success (and a lot of fun), thus far it has only been available as a soldering kit. Today, we’re pleased to supplement those with a new version: prefabricated Octolively modules, all built-up and ready-to-use, so you can jump right in and start playing with the LEDs.


Octolively Modules

Like the soldering kit version, each “prefab” Octolively module is 4 × 8 inches (10.16 × 20.32 cm) in size, and features eight huge (10 mm) ultrabright LEDs, spaced along a two-inch grid.  And, for every LED, there is an independent infrared proximity sensor pair, configured to act as a reflective motion sensor.
Octolively Modules

The most obvious change from the soldering kit version of Octolively is that the topside components take up a lot less space. All of the resistors, capacitors, and the microcontroller have been replaced by their surface mount equivalents.


Octolively Modules

However, this not really a “surface mount” circuit board, it’s more accurately a “mixed technology” board.   Some of the components— in particular many “optoelectronic” components, like our visible and infrared LEDs —just don’t have great surface mount versions.  For example, when we’ve tried building motion sensors circuits with SMT infrared LEDs (even the pricier types that have itty-bitty lenses) we found that they just didn’t project enough IR light to be effective. Similarly, we’ve found that visible surface mount LEDs tend to be perceived as dim, even when a huge amount of light is being emitted, because the light usually goes into a very wide angle.


Octolively Modules

The microcontroller is an Atmel ATmega164A, in the 44-pin TQFP package.  (And in case you’re wondering, yes that’s exactly as redundant as “ATM machine.” )

Those white gumdrop-looking things are (as before) the big 10 mm LEDs, but they certainly seem even bigger sitting next to that chip.


Octolively Modules

Ready-to-use Octolively modules are available now at Evil Mad Science.

Additional details— including the datasheet and documentation links —are available on the product page.

Return of the Peggy Projects

One of the great things about building electronics projects is seeing what they inspire other people to do, and the 625 LEDs of the Peggy 2 can be pretty inspiring:

Mark at awe.com did some awesome scrolling text on Peggy 2 and has even shared his sketch for others to use. His video is embedded above or you can click on over to YouTube.

Phillip at peilipu’s posterous hooked up a Peggy 2LE and a Danger Shield to play Pong, a game we’re rather fond of.

Nick over at NJS Shredding wired up an off-board Peggy 2, neatly built into a wooden box and mounted to the ceiling. He also posted a video which shows the scale of it quite well.

Another ceiling mounted Peggy 2 installation was recently posted on the Make blog. This one, with an amazing array of ribbon cables connecting strips of LEDs, is entertaining visitors at the Children’s Museum of Pittsburgh and was created by the late artist Rick Gribenas. Thanks to Matt Mets for sending us the picture!

Also at a museum in Pittsburgh, Deren Guler used a Peggy 2 in a kid-powered generator exhibit at the Carnegie Science Center. Thanks for sending the picture, Deren!

You can read more about Peggy 2 on our store here, and full documentation is available on our wiki here and links to more projects are posted there as well.

Interactive Game of Life Kit

Game of Life 6

Game of Life 4

Game of Life 12

Two years ago we designed an interactive exhibit of Conway’s Game of Life for the San Jose Museum of Art. The hardware that we used for that project eventually became the basis for our Octolively interactive LED kits.

We’ve recently had occasion to revisit our Game of Life project, and to build an all-new version of the museum exhibit. Along the way, we’ve rewritten the firmware from scratch and added a number of features. And today we’re pleased to announce the result: our new Interactive Game of Life Kit.

Continue reading Interactive Game of Life Kit

Alpha Clock Five


What’s cooler than itty bitty alphanumeric LED displays? Freaking huge ultrabright alphanumeric LED displays, that’s what!

And so today we’re releasing a new kit, the Alpha Clock Five, an open-source, hacker-friendly alarm clock kit, based around an block of fiveultrabright red 2.3″ character height alphanumeric displays:


So, how big are these things?

For scale, here’s one of the displays next to a Diavolino board:


These displays are great in many ways– they’re extremely bright for one –but the downside is that they are actually a bit tricky to drive. The 10 “big” segments each have two LED elements in series, twice in parallel, while the smaller segments have two LED elements in series, but not in parallel, and the decimal points each have a single LED element. To drive each LED element at (for example) 25 mA and 2 V requires 4V, 50 mA to be provided to ten segments, 4V 25 mA to the six short segments, and 2 V at 25 mA to each decimal point. And, it’s a fair number of signals to manage as well.


To solve the problem, we designed a multiplexed driver board, with two LED driver chips at different current set points. A 16-bit constant-current LED driver is preset at 50 mA and drives the ten large segments, while a separate 8-bit constant-current LED is preset at 25 mA and drives the short segments and the decimal place. The multiplexing is in analogy with an LED matrix, where each alphanumeric character comprises one row of our matrix– which just happens to have 54 LED elements inside. One row is switched on at a time by one of five transistors. We used high-current, low-saturation-voltage PNP transistors, type 2STX2220– the low saturation voltage means that you *can* use these to switch a useful 4 V load, even when running at 5 V.

The circuit board is 9.430 X 2.736″ in size, and extra stiff at 0.094″ thick in order to support those heavy LED displays in their sockets. An ATmega644A microcontroller runs the show, and is preloaded with a bootloader so that you can program it like a Sanguinoboard, through a version of the Arduino IDE with added extensions. There’s also a magnetic buzzer so that it can be a full-on alarm clock, and a spot for a Chronodot module, for good timekeeping and battery backup.


Here’s what the front of the “brick” looks like, with the five displays socketed next to one another. There are four right-angle tactile button switches hanging off of the top edge, so that you can adjust the time, alarm time, brightness, and so forth. If you hold the two rightmost buttons for a couple of seconds, it brings you to the options menu, where you can (for example) switch between 12 and 24 hour modes:
The circuit board, laden with alphanumeric displays, sits inside an acrylic case:


The front side of the case is deep red transparent acrylic (#2423 red transparent, should that come in handy), and serves to increase the contrast of the displays. The back of the case is gray transparent acrylic, and the top and bottom are black. The top surface has engraved labels for the four buttons, and four button keys cut into the acrylic. The thin beam flexes easily, contacting the right-angle switch below, when the circuit board is there.


The back of the case is transparent so that you can see the circuit board. There’s also a white LED “night light” on the circuit board that can be enabled or disabled with the top buttons, and the sides are open to provide easy access to the TTL serial interface.

Obviously there’s a lot that could be done by hooking up a nice 5-character alphanumeric data display device to your computer.


On top of everything else, Alpha Clock Five is also a full-fledged alarm clock, right down to the snooze mode— although the word “SNOOZE” didn’t quite fit on the display (it says “SNOOZ,” if you must know).

Perhaps the biggest challenge for making it “bedroom compatible” was that it needed to not just be able to be extremely bright, it also has to be able to go crazy dim– which it can do, with fourteen levels of adjustable brightness.

And it has some fantastic features as an alarm clock– for example multiple alarm tones and digits that are big enough to see even if you normally wear glasses.

And with a bit of code, it can be so much more. Soon, yours might say spell out “TRACY WAKE THE HECK UP” or use a couple of its spare I/O lines– and only make you coffee if you actually manage to get up on time.

Alpha Clock Five is available now at the Evil Mad Scientist Shop.

Improving the Menorah kit



One of our favorite little kits is our Deluxe LED Menorah kit. Since we introduced it two years ago, one of the most common questions that we get asked is this: “Can you use candle-flicker LEDs in it?” And thatturns out to be a very interesting question.



The simple– but, alas, naive –answer is “yes.” We have discussed candle-flicker LEDs in the past, and in most cases, yes you candirectly substitute them for regular LEDs.


But if you do go ahead build up a menorah kit with the candle-flicker LEDs,
what you will find is that the performance is simply terrible: Not only do these LEDs fail to perform properly– (there is no “candle flickering”), but they actually exhibit behavior that we might categorize as “not even wrong”– the LEDs are not particularly steady either, but are rather a bit weak and jittery.


The reason for this is that in the kit, the LEDs are not left continuously it, but are instead continually– and far too quickly for the eye to see –pulsed on and off. This is done because the menorah kit uses pulse-width modulation (PWM) dimming to produce a range of different brightness levels. Not only does the menorah have two different selectable brightness levels, but it also has the ability to softly “fade in” and “fade out” the LEDs when they light up or switch between the brightness levels.


In most ways, this PWM dimming is a wonderful thing. It allow us to create these gentle fades and different brightness levels, and allows us to really fine-tune the performance for better power efficiency. While this works extremely well for regular LEDs, each of the so-called “candle-flicker LEDs” is not just an regular LED, but is actually a regular LED packaged with a tiny integrated circuit that executes the “random flicker” program. And, that chip can only execute its program properly if it’s left on continuously. If instead, it is continually pulsed on, we might indeed expect to end up with the kind of jittery, inconsistent behavor that we do see in the kit.



How could we go about fixing this, if we wanted the LEDs in our menorah to flicker? It would be straightforward to remove the dimming features from the software, and actually use the self-flickering LEDs in a mode where we leave them on continuously. But in doing so, we would lose a couple of our favorite features: the gentle fade-ins that make the kit so elegant, and the ability to have multiple brightness settings.



So that’s a tough choice: Do we forgo flickering, or live without our elegant gray scale fades?


But fortunately, there is a way out. The right solution is to remember that we do have a microcontroller– an ATtiny2313 –running the show, and to start acting like it. If we go back to regular (non-flickering) LEDs, we should be able to write a “random walk” flickering algorithm and add that to our existing firmware. In doing so, we can keep our original fades and brightness modes. We also can keep the kit price the same (since we don’t need the more expensive flickering LEDs), and as a hugeadded bonus, we can now turn on or turn off the flickering at will– something that you can’t do with LEDs that always flicker.


Today we’re releasing the new version of the menorah kit software, and shipping it in the kits. And, we made a little video(embedded below) to show off the new flicker modes and what happens when you try and use flickering LEDs with PWM:




The new source code– Menorah kit software version 1.3 –is available here, and it can be used to upgrade any older Deluxe LED Menorah kit as well. :)

Halloween Projects from Evil Mad Scientist Laboratories

The Great Evil Mad Scientist Laboratories Halloween Project Archive!

Halloween is one of our favorite holidays, and our collection of Halloween projects continues to grow. Every fall we update it to include our latest projects for the season. In the list that follows, we’ve organized dozens of our Halloween projects into categories: costumes, pumpkins, decor and food.

Last updated: 10/2019.

Continue reading Halloween Projects from Evil Mad Scientist Laboratories