Challenge: Figure Out How This Logic-based Chaser Works

January 25, 2012 by Mike Szczys 37 Comments

[Andrea] built this LED chaser using one logic chip. It illuminates all but one of the six LEDs, with the dim bit moving back and forth along the row in a chase sequence. This is something like an inverse Larson Scanner without the fading tail. But doing it with a logic chip instead of a microcontroller is a fun challenge.

Which brings us to the point of this feature. [Andrea] didn’t really post an explanation of how the circuit works. Usually missing details mean that we archive the tip and move on to the next one, but we think this provides a fun activity. Can you figure out how the circuit works? We already know that it’s using a CD4017 decade counter/divider chip. This gets its clock signal from a 555 timer circuit. [Andrea’s] schematic is a bit hard to read, but grab a copy, blow it up a bit (or use your browser zoom) and study the CD4017 datasheet (PDF) if you need to.

Want proof that it does actually work? It’s embedded after the break.

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Monitoring Batch Jobs The Cylon Way With Python And A Parallel Port

November 18, 2011 by Mike Nathan 14 Comments

parallel-port-trigger

If you happen to do a lot of video encoding, you know that your computer can really drag while the process is carried out. Our own [Mike Szczys] transcodes videos at home fairly often, and because the process is automated, he doesn’t always know if a conversion is taking place in the background.

He has been tinkering with Larson Scanners recently and thought he could put everything he’s learned along the way to good use by using the scanner as a “busy” indicator for his PC. He hooked the scanner up to the computer’s parallel port, and took a few minutes to bang out some Python code that would alert him when his PC was busy.

He set his notifier script to launch along with FFMPEG, whenever his MythTV setup had something ready to convert. The Python script drives a pin on the parallel port high, triggering the Larson Scanner’s animation. Every minute, the script checks the status of FFMPEG and continues to hold the pin high until the application exits. Once the conversion is done, the scanner goes back to sleep, letting [Mike] know that the coast is clear.

Check out the video below the break to see his parallel port trigger in action.

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Controlling Shift Registers Via SPI

November 5, 2011 by Brian Benchoff 12 Comments

Hack a Day’s very own (and very prolific contributor) [Mike Szczys] put up a great tutorial on how to drive shift registers with an SPI interface.

[Mike]’s earlier tutorial of the 595 shift register goes through the functions of a shift register pin by pin. In a 595, bits for each position in the register are sent over one at a time. Most microprocessors have an Serial Peripheral Interface, and using an SPI bus means a lot less mucking about.

An ATmega168 was used for this build, although most Atmel chips can be made to work as an SPI master device. There are just three wires connecting the microcontroller to the shift register – SER, SRCLK, and RCLK. Like any other shift register setup, the build can be expanded by connecting the QH’ pin of the first 595 to the SER pin of the second.

[Mike] graciously made all the code for his build available. The video after the break is a 16-bit binary counter, a good stopping point before [Mike] rebuilds his Larson scanner/Cylon/Kitt, moving away from a PWM-based build to a register-based one.

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Detailed Tutorial Shows How To Unleash Your Inner [Michael Knight]

October 28, 2011 by Mike Nathan 12 Comments

developing_a_larson_scanner

Our own [Mike Szczys] recently sat down and put together a great tutorial on building a Larson Scanner. The ubiquitous circuit is usually one of the first few projects on a budding hackers list of things to build, since they are just so darn fun.

Simple versions of the scanner sweep back and forth lighting the LEDs without any sort of transition between them. The configuration most familiar to us all as featured in Knight Rider and Battlestar Galactica are a bit more complex, and have a fading trail of light that follows behind the leading edge of the sweep. [Mike] notes that this fading is traditionally accomplished through the use of capacitors, which cause the light to gradually fade as the animation sweeps across the LED array. He decided to take a different route with his circuit, relying on PWM control of the LEDs instead.

Mike put together a simple circuit using an ATmega168, a handful of resistors, and of course, an array of LEDs. Utilizing interrupts and PWM, he was able to accurately recreate the iconic light sweep without the use of any capacitors. One big benefit to his design aside from the lower component count is the fact that he can easily adjust the speed of the sweep as well as the fading properties with a few small code tweaks.

Be sure to check out his blog at some point, where he shares his code, some circuit diagrams, and plenty more details on how his scanner was built. In the meantime, take a look at the video below to see the result of [Mike’s] work.

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Kraftwerk Inspired LED Tie

September 1, 2011 by Mike Nathan 16 Comments

If you didn’t land the job after your last interview, it might have been because you were not wearing this sweet Kraftwerk-inspired necktie. Although our own [Caleb Kraft] insists that this recent creation by the folks over at Evil Mad Scientist Laboratories is a tribute to him, [Ralf Hütter and Florian Schneider] beg to differ.

The inspiration for the tie actually comes from Kraftwerk’s 1977 video for “The Robots”, in which the band wore black ties with embedded scrolling LEDs. The effect is very similar to that of a Larson Scanner, though Kraftwerk’s ties light the LEDs in a single direction and do not fade in and out.

EVMSL has released a firmware update to the Larson Scanner they sell in their shop that replicates the Kraftwerk effect, and they also put together a quick tutorial showing how you can construct your own coin cell-powered LED tie. We’re not suggesting that anyone rush out and buy their kit, as it can be replicated fairly easily – we just thought it was pretty cool.

So, if you’re looking for a retro-inspired Halloween costume, search no further – Evil Mad Scientist Labs has you covered.

Continue reading for a video demo of their tie, as well as the original video that inspired it.

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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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Larson Scanner Hacking

October 14, 2010 by Caleb Kraft 13 Comments

more MORE MOOOORRREEE

We all love a good larson scanner. They’re so iconic that Evil Mad Scientist Laboratories makes a kit. However, just getting a kit and building it isn’t enough for many of us. How would we make a larson scanner better? Simply by adding more. EMSL shows us how you can modify their kit in both hardware and code to chain them together. They detail the modifications very clearly and show some video examples. You can see a three larson scanner chain in action after the break.

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