Cautionary Tales of Power

When doing an LED electronics project, there seem to be three big “P”s that have to be tackled:
1. Pixels (which ones, how many, what configuration?),
2. Programming (what do I want, and how can I do that?), and
3. Power (how much, from where, and how do I distribute it?)

And people (by which I mean: perpetual newbies like me) tend to do them in that order: first wire up some pixels, then program them, then figure out how to power it all for real.

And of course, this often leads to a problem where you get stuck between steps 2 and 3, where you have your creation sort of up and running on the lab bench — but now there’s this little problem of how to power it, and you have to go back and rethink and rework other parts of the project to accommodate the power situation.  So it’s worth planning for power from the start — which is easy to say, but hard to do!

What could possibly go wrong? (A list)

So what happens if you don’t plan for power? Well, here are some power problems that I have personally had. How many of these can you diagnose just from the description?  (“Failure to plan” is a nice catch-all phrase here if you get stuck.)

  • Hrm, now how do I get power all the way up there?
  • Gee, that’s a long run of wire… but if I use fat wire, it’ll be expensive and heavy and cumbersome. Nah…
  • I’ll use skinny wire, it’s much cheaper… Hey, why is it only reading 4v at the far end? And does anyone smell something burning?
  • OK, I switched to thicker wire, and I’ll just re-use the power connectors from before. Holy cow now the connectors are getting hot!
  • Fine, I’ll switch to these big thick nonpolarized connectors. Huh, that’s odd, it’s not working now. Does anyone smell something burning?
  • For this other wearable project, I’ll use a simple battery holder and regular alkaline batteries… hey… why are the colors so ‘warm’.. no blue? And now no green, too…
  • OK, switching power to one of those ’emergency phone chargers’ that takes AAs and puts out 5v from a USB socket. Hey! Why are the batteries dying so fast?
  • OK, fine, I’ll switch to this lithium battery pack… hey, it said 5000mAh… so why did it stop powering my 5000ma project after only half an hour?
  • How come my WS2811 project works fine from my computer, but then flickers like crazy when I power it from this cheap USB wall power adapter?
  • For this big outdoor project, I’ll use this big, burly 12V lead-acid marine battery. Hey… how come it won’t hold a full charge after the first time I let the lights go all night?
  • Everything was working fine yesterday, before last night’s rain!
  • Everything was working fine yesterday in the cold and snow, so it should be working fine today now that it’s warming up, right?!
  • I think I’m going to switch microcontrollers.  The old one had a power regulator that could handle 12v input.  Hey… do you smell something burning?
  • Why is this power switch getting hot now? And why is it now totally stuck in the “on” position? And … do you smell something burning… again?

So: Plan For Power.

The lesson to learn here is that for basically any real project, calculate and plan the power first.  Before you wire up any pixels. Before you write any code. Just stop for a minute and think about how much power you’re going to need, and where it has to come from, and where it has to go.

Use on-line calculators that will help you figure out how much power you’re going to need, and what gauge wire you’ll have to use given how long your cable runs are going to be.  I also really like the “LEDstimator” app for iOS to help explore some “what-if” values for things like wire gauge.

And above all else… uh… wait… do you smell something burning?


FastLED for the Apple II: Hack to the Future!

These days, I hack LEDs.  I’m the co-author (with Daniel Garcia) of the FastLED library for driving tons of high speed LED pixels and strips using microcontrollers like Arduino and Teensy.

But back in the day, I hacked a lot of Apple II.  I published a couple of shoot-em-up games (with Geoffrey Engelstein), all written in lovingly hand-crafted 6502 assembly language.

Finally I decided it was time to link the present to the past: to connect a hundred high-speed RGB LEDs to an Apple II, somehow, and ‘port’ our FastLED library to 6502 assembly language.

Well, I did it, and it works.  My new creation, “FastLED6502”, can drive a hundred 24-bit RGB pixels at more than 30 frames per second from an Apple //e :

The Details

Here are the details of “FastLED6502”:

  • “FastLED6502” is a lightweight port of FastLED’s core functions to 6502 assembly language for the Apple ][, Apple ][+, Apple //e, and Apple //gs.
  • Supports APA102 / Adafruit DotStar LED strips, as well as LPD8806 and WS2801 (though those two are not fully tested yet).
  • The LED strip is connected to the Apple II using the 16-pin DIP game port on the computer’s motherboard.  The 9-pin DB joystick/mouse port on the back of the //c, //c+, and //gs cannot be used, as it lacks the TTL digital output signals needed to drive the LED strip.
  • 24-bit FastLED Rainbow colors are included, along with FillRainbow, Random8 and a number of other useful functions from FastLED’s main library.
  • Everything had to be re-written from scratch in 6502 assembly language.  Luckily(?), I still remember how to do that.
  • The assembly code knows the binary serial protocols for the APA102 (Adafruit DotStar), LPD8806, and WS2801 LED driver chips.  Depending on which one you select, FastLED6502 transmits the LED colors in the correct protocol over the game port TTL digital output lines.
  • Considering that the Apple II sports a 1MHz 6502 so slow that even a “NOP” takestwo cycles, overall performance is pretty good: more than 30 frames per second for a 100-pixel strip.
  • Speaking of speed, or lack thereof, “three-wire” clockless LED strips such as the WS2811 NeoPixel are not supported now, nor will they ever be.  The CPU is would need to be at least 20X faster to support them, and it isn’t.  For that you want an Arduino or Teensy, and FastLED proper:
I gave the code its public debut at Veracode Hackathon 7.  (The theme was “Cozy Cabin” — I don’t usually wear plaid.)
I don't usually wear plaid.

FastLED6502 at Veracode Hackathon 7

How’s it work?

So how does this all work? Well, you connect the CLOCK and DATA_IN pins from the LED strip to a couple of pins on your Apple II’s DIP game connector port, add power, and you’re ready to go.  The Apple II’s game connector not only has inputs for joysticks, paddles, buttons, and so on, but it also has a few digital outputs — and that’s what FastLED6502 uses to deliver signals to the LED strip.  On all the 16-pin DIP Apple II game ports (except for the //gs!), there’s even one pin that delivers a super-fast digital pulse; pin 5 is the C040STROBE line, which can pulse twice as fast as the other digital outputs.  If you choose that for your CLOCK pin, the FastLED6502 code automatically shifts into high gear, and you get faster performance.   FastLED proper does this, too, in a much fancier way; it’s amusing that ‘little’ FastLED6502 does some of this, too.

The Code

The code is in the “extras” directory here (and eventually on FastLED’s main branch, but not yet)
Here’s the FastLED6502.s65 source code itself: here’s the RainbowDemo.s65, as shown in video:

This is Crazy

Overall, this bit of code is completely nuts, and we don’t expect anyone to use it.  At all.  Ever.  Accordingly, we’re not going to really support it, either.  At all.  Ever.  It was a labor of love and a creation of pure modern retrocomputing insanity.  But here it is, in all it’s insane glory, “FastLED6502”.
And now, if you cut me, I’ll bleed 16,777,216 colors at thirty frames a second.

Iteration impels improvement.

This thing that I am casually holding up in one hand is an 7′ x 3′ LED tapestry, plus diffuser, plus controller box, plus all mounting hardware, plus power supply and extension cord (rolled up inside for easy transport). It’d fit in the carrying bag for a folding camp chair.


Now, truth be told, I’m not crazy about the layout of LEDs on it (too gridular)…


…so there will be at least one more iteration of this “small” one before I build the “big one” for playa. But. It feels good to have come this far: the previous incarnation had to be wheeled around in a suitcase, and required complicated mounting due to it’s own weight.

Next iteration will focus on making the layout more ‘organic’ (the way I like it), and continuing to rethink how the diffuser is held at the right distance from the light.

Lanyard-mountable LED throwies

At the last “HacKidThon”, we showed a passel of kids how to make LED “throwies”. Each one is a nothing more than an LED, a coin cell battery, and a magnet so the contraption can stick to metal surfaces, walls and buildings, and hang there glowing.

This week, someone asked me if we could modify the classic design somehow so that the LEDs could be attached to lanyards, instead of magnets. We wanted it to be as cheap and easy as the rest of the “throwie” recipe.

A little brainstorming with Eleanor, and we came up with this: plastic-coated paperclips!


The paperclips actually help hold the LED leads in place; we put tape around them as usual, though that’s not shown in the picture. The plastic coating keeps the paperclip from shorting out the positive and negative battery terminals.

The coated paperclips cost less than a penny apiece, and come in colors that match the LEDs. Victory!

Easter Egg Hunt Rules, 2014.

We love doing Easter egg hunts.  But as the girls get faster, smarter, and more wily, merely finding the eggs is no longer challenge enough.  I’ve gotta slow ’em down somehow, and this is how I do it: each girl gets an empty basket (I use traditional Jack-O-Lantern baskets), and sheet of instructions helping her know which eggs are for her, and which are for her step-sister.  Each year, the instructions require more careful reading and invoke increasingly complicated rules.

New this year: the contents of two of the eggs altered the interpretation of rules, retroactively. This fact itself was part of the published rules… this time.




The best part was watching the girls excitedly pounce as they found the first eggs, and then stall completely as they had to stop and puzzle out exactly who’s egg it actually was that they’d just found.





P.S. Here are the previous year’s Egg Hunt Rules (2013):


Fire2012: an open source fire simulation for Arduino and LEDs

I’ve built and programmed a couple of different ‘fire’ simulations for Arduino and LEDs, and I’ve had numerous requests over the years to share the source code.  I’ve always been happy to share my work; the holdup has been that before I share my code for the world to peer at, I like to clean it up a little.  I like to give the code a clean shave and scrub under its fingernails before it steps out onto the wide open Internet where it might have an audience with Her Royal Majesty, The Queen of England.  It could happen.

Anyway, I finally cleaned up the code for one of my simplest and most legible ‘fire’ simulations, and I give it to you, your Majesty, and everyone else, too. Here’s a video of the code in action on a 30-pixel strip of WS2812B LEDs (or maybe WS2811) and an Arduino.  Source code link is below the video.

Full source code is here:  The simulation itself is only about 25 or 30 lines of code.  It uses our (open source) FastLED library to drive the LEDs.

Discussion about the code and how to port it and use it are here on the FastLED discussion group on G+




If I’m confused, it must be playtime.

Some things we try because we have a clear idea where we want to be and a clear idea how to get there.

Some things we try because we’re suddenly shocked to find that the heretofore completely impossible has suddenly and surprisingly come within practical reach.

And some things we try just to play, and to explore what if. We start with our heads full of simple ideas that turn out to be wrong, and we awkwardly replace them in torn out bunches with new confused half-understandings that, later, will let us reach something wholly unexpected.

I’m not sure which of these things in doing here, which means it’s probably that last one.



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