A Beginner’s Guide To LED Matrices

April 29, 2011 by Mike Nathan 4 Comments

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[Rajendra Bhatt] wrote in to share a tutorial he put together demonstrating the basics of using LED dot matrix displays. While this subject might be old hat to many out there, his helpful walkthroughs are geared more towards beginners who are exploring various electronics concepts for the first time.

He explains the theory behind LED displays using a PIC-driven 5×7 matrix as an example. He discusses persistence of vision and how tricking the human eye can save you quite a bit of time and a whole lot of pins. Multiplexing is broken down into its most basic steps, which [Rajendra] illustrates by showing how a letter would be drawn on the LED display one column at a time. The use of a ULN2803A Darlington Array is also discussed, and he details why it is used when pulling the five columns of LEDs to ground.

The only portion of the tutorial we thought could be expanded upon was the programming section. While he does show how each letter of the alphabet can be displayed via a series of five hex values, he does not cover the “why” part of the process. Obviously while anyone familiar with binary and hex can figure it out in pretty short order, we think that it would be a great place to pause and expand the readers’ knowledge even more.

Overall it’s a useful tutorial, and most beginners would likely find it quite helpful.

The Start To Finish Of An Interactive Exhibit

April 29, 2011 by Mike Szczys 7 Comments

[Andrew & Deborah O’Malley] were tapped to created an interactive exhibit. The mission was to show that social problems take continual support from a lot of people before they can be solved. The piece needed to be architectural in nature, and they ended up building this touch-sensitive model building with individually lighted windows.

The project log that the [O’Malleys] posted shows a well executed battle plan. They used tools we’re all familiar with to achieve a highly polished and pleasing result. The planning stages involved a virtual mock-up using Google SketchUp. The details needed to order the shell from a fabricator were pulled from this early work, while the team set their sights on the electronics that shed light and that make the piece interactive. The former is provided by a Shiftbrite module for each window, the latter comes from the Capacitive Sensing Library for Arduino. Despite some difficulty in tuning the capacitive grid, and getting all of those Shiftbrites to talk to each other, the exhibit went swimmingly. It’s not hard to imagine how easy it is to start a conversation once attendees are attracted by the seductive powers of touch sensitive blinky lights.

Small POV Device Shows Off Some Big Features

April 26, 2011 by Mike Szczys 21 Comments

We’ve already added the components needed to build [Rucalgary’s] tiny POV device to our next parts order. The little device sets a new standard for tiny persistence of vision boards. Instead of relying on the user to find the best speed and timing for swinging the board around, [Rucalgary] used an accelerometer. This is the point at which we’d usually groan because of the cost of accelerometers. We’re still groaning but this time it’s for a different reason.

The accelerometer used here is a Freescale MMA7660. It’s an i2c device at a super low cost of less than $1.50. The reason we’re still groaning is that it comes in a DFN-10 package that is a bit harder to solder than SOIC, but if you’ve got patience and a good iron it can be done. An ATmega48 drives the device, with 8 LEDs and one button for input. On the back of the board there’s a holder for a CR2032 coin cell battery and a female SIL pin header for programming the device.

Check out the video demonstration embedded after the break. We love it that the message spells and aligns correct no matter which way the little board is waved.

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Papydoo Is Watching You!

April 26, 2011 by Jason Komp 6 Comments

Papydoo spends most of its time sleeping, but if startled by vibration it will wake up and stare you down with a cold and unnerving robo-gaze like you have not seen before. Or it might just do something crazy like display a scrolling Space Invaders character marquee. That’s the thing with Papydoo, you just never know.

Vibration sensing is accomplished with a piezo element harvested from an old horn speaker that is simply sandwiched between the project enclosure and the surface it is sitting on. A MCP601 op-amp is used to amplify the weak potentials from the piezo element and feed them to the ADC of a Zilog Z8F083A microcontroller. When sufficient vibration is detected, the MCU wakes up and displays one of a number of different animations on the front panel 32X8 LED matrix. The various display modes can also be manually selected using a small button on the back of the enclosure.

Power consumption is reduced to 150uA while sleeping by only briefly waking the MCU once per second to check the current vibration level. Nearly all of this power draw can be attributed to the op-amp, and although there are much more efficient models available, sometimes the best choice is just the one you already have on hand in your parts bin. Regardless, the power consumption is low enough to run the device off of a set of AA batteries.

We could imagine that similar setup could be used for a number of different low-powered messaging applications that would only “wake up” when someone was near enough to read and interact with. Add a loud speaker and this might even make a good alarm to keep pesky coworkers out of your “cube”. What would you do with a Papydoo?

Thanks for the tip [Laurence]! If you happen to read this, we are dying to know: why “Papydoo”?

Short video after the break.

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Mini LED Message Board Built From Retro Displays

April 24, 2011 by Mike Nathan 19 Comments

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[Iain] is getting to the point in his life where he finds himself waxing nostalgic about various different technologies from his youth. One item he has always been fond of is first generation 7 segment consumer LED displays, like those found in old calculators.

He was excited to find one of these displays at the bottom of a box full of electronics odds and ends he received from a friend. After identifying the display and tracking down a data sheet online, he decided that he wanted to build some sort of little gadget out of it.

His first inclination was to build a tiny text scrolling gadget from the display, and thus his “Personal Electronic Retro Telegram” (P.E.R.T) was born. With Arduino in hand, he prototyped the circuit on a breadboard, then sent away to have some PCBs built. Once he received the boards, alll of his prototyping components were swapped out with SMD versions, including a TQFP ATMega168 chip in place of the full-sized Arduino board.

The final result is a nice melding old and new technology which he decided to give to his girlfriend as a gift. Continue reading to see a quick video of the P.E.R.T in action.

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Hacking Cakes With LEDs

April 23, 2011 by Mike Nathan 25 Comments

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A large part of science is making mistakes and learning from them in order to make each subsequent design that much better. When your experimentation involves hacking cakes, each failure is an exercise in deliciousness.

[Craig] and his group of research partners often bake electronics-related cakes whenever part of the team departs in search of other opportunities. Over the years, farewell parties have seen renditions of anything from multimeters to quantum computers. This time around, he wanted to make something that contained actual electronics parts, while still remaining edible.

He settled on making an LED matrix inside of a cake, using silver foil wrapped licorice for wires. In the end however, he found the silver foil to be incredibly difficult to work with, and the matrix ended up being little more than a few randomly blinking LEDs.

Even though things didn’t work out quite how he planned, he is not discouraged. The cake was still quite tasty, and through this process he has discovered edible silver paint, which will undoubtedly make it into the next farewell cake.

Larson Scanner Using 7400 Series Logic Hardware

April 20, 2011 by Mike Szczys 11 Comments

[RandomTask] is sharing a Larson scanner he built a few decades ago. These days you can whip one of these up using an Arduino in under an hour. He mentions this, but we agree that for nostalgic purposes there’s nothing like implementing the scanning LED effect using hardware.

Often called a Cylon Eye (after the television show Battlestar Gallactica) or referred to as the lights on the front of Kitt (the car from Knight Rider), the effect doesn’t just involve switching LEDs on and off in the proper order. A true Larson Scanner fades the LEDs as the bright point moves away from them, resulting in a tail that dims over time.

This implementation uses a 555 timer as the clock signal, allowing for speed control through a potentiometer. A counter chip, J-K flipflop, and line decoder all work with each other to address the movement of the brightest light. The fading effect is managed via a capacitor and resistor for each LED. The video after the break shows the pleasing result of this setup.

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