Stuff Andy Makes – DIY, make, tinker, play

Charlieplexing LEDs with an AVR ATmega328

Apr 29

AndyEducational/Interesting, Electronics, Miscellaneous, Projects, Tips and Techniques atmel, avr, charlieplexing, led, microcontroller, pcb 3 Comments

This is the first in a two-part series. This first article made me realize there’s a lot of ground to cover and we’re already in the tl;dr territory.

How many times has this happened to you? You have a little LED project with an AVR ATmega328 microcontroller (or Arduino) at its core and you need to light up a boatload…. A dingyload of LEDs. Maybe it doesn’t happen a lot to you. It’s happened on three recent projects for me. My latest two LED projects are a timekeeping piece that illuminates 21 characters from behind and a simple LED chaser thing.

As usual I wanted to keep the component count down on these projects. I also tend to prefer not to use a ton of ICs with busses between them and whatnot, if I can help it. So much darn soldering and stuff. Meh. Luckily, back in 1995, so the Wikipedia story goes, a super-smart dood named Charlie Allen at Maxim Integrated devised a super-ingenius way to control a large number of LEDs using a not-so-large number of microcontroller pins. The method is called, “Charlieplexing” and it seems a but daunting, at first, but it’s not that bad once you figger it out.

The core of this concept is based on the fact that diodes only allow current to flow in one direction. The “D” in “LED” stands for “diode.” Ergo, LEDs are diodes. LEDs only light up when connected a particular direction. Put two diodes in parallel BUT in the opposite-facing direction and you can turn on one or the other simply by switching the polarity of the ends of the circuit. Fun! Diagram:

Two LEDs in Parallel

Let’s assume I have a 3V little coin cell running this thing and limiting resistors and CCRs are not our thing, today. Why not? Anyhoo… Looking at the diagram, you see I’m using GPIO pins from an Atmel ATmega168 AVR microcontroller (it was readily available in the library in Fritzing, the program I used to throw together the drawring diagram schematic thing above). If I configger A0 and A1 as outputs and then set A1 HIGH and A0 LOW, I can turn on LED1. If I flip the states of the two pins and make A1 LOW and A0 HIGH, LED2 will light. Here’s a animated GIF of how it works with direct connections from the LEDs to 3V lithium coin cell on a breadboard:

Parallel opposite polarity LEDs flipping state

Watch carefully and you’ll see that I switched the positive and negative to make one or the other LED light. Easy as pie. Imagine each wire from the battery is a GPIO pin from a microctonroller. All I’m doing up there is making one HIGH and one LOW and then flipping them back and forth.

More

meltmedia meltHack-A-Palooza V: The Lost Pushbutton

Apr 07

AndyEducational/Interesting arduino, coding, electronics, hack day, meltmedia, microcontroller, MSP430, pelican case, pizza, rotary encoder No Comments

Every few months I organize a hack day at the office, usually on a Saturday. This past Saturday we had our 5th installment of hack/make/tinker day at meltmedia and the turnout was great! Attendance was 8, up from 3 the last time around. YESSS!

meltmedia East Kitchen Table Hacking

Nick put together a little video of the goings on:

Or click here to see meltmedia Hack Day | April 6, 2013 from meltmedia on Vimeo.

We had all manner of making and designing, but most importantly, around 1:30-ish, we had PIZZA!!

Fueling the Making with Pizza

More

Disney “Glow With The Show” Ears Teardown

Jul 08

AndyTeardowns batteries, capacitive touch, Disney magic, flexible PCB, IR receiver, led, microcontroller, MSP430, RGB, Texas Instruments 3 Comments

On the way to lunch, one day, our CTO told us about this amazing show they put on at Disneyland called, “World of Color” in which all of these special “Glow with the Show” mouse ear hats changed their glowing colors in sync with the show. Of course, the car full of techies and nerds instantly got to speculating on the tech behind it all.

Disney Glow with the Show Magic Mickey Ears Hat (Pre-Teardown)

UPDATE (2012.08.17): I received a linkback from the Disneyland Resort Update website where they had a video of one of the imagineers explaining more about the hats in this YouTube video: http://youtu.be/TbxkrpWu7hQ

The CTO recently visited Disneyland in California and bought me one of the special “Mickey Ears” hat with RGB LEDs in the ears. They have a little metal touch sensing button to turn them on and off. When on, they rotate through different colors which get diffused in the translucent white plastic ears. Of course, color rotating with RGB LEDs is not-so-advanced and I’ve done it many times (see the Mood Lamp for my wife). More

Desktop Warp Core – The Early Years

Jul 21

AndyMiscellaneous 12V, avr, desk toy, electronics, fiberglass, lathe, LEDs, microcontroller, MOSFETs, Next Generation, Star Trek, transistors, warp core, woodworking No Comments

Well, we’ve moved into a new and larger space at the office and we sit at these massive wood and steel desks as teams. Our team decided we needed more “flare” at our desk, so, of course, a big-ass warp core was the first thing that popped into our heads. How hard could that be?

The rings of the warp core will be clear-ish fiberglass. The original master, over which we’ll make a fiberglass mold for all eight rings, is made of a giant laminated wood block we need to turn on a big lathe.

Laminating 2x6 pieces of pine for the ring master mold

More