Saturday Clock: An 0.000011574Hz ATtiny85 clock

In these times when we try to squeeze out extra clock cycles by adding more cores to our CPUs and by enlisting the aid of GPUs, [Ido Gendel] thought it would be fun to go in the exact opposite direction, supply a clock to the ATtiny85 that cycles only once per day, or at 0.000011574Hz. What application could this have? Well, if he could do it in seven instructions or less, how about turning on an LED at sunset Friday evening, to indicate the start of the Jewish Shabbat (Saturday), and turn it off again at sunset Saturday evening.

Notice the subtlety. A clock that cycles once per day means you can execute at most one instruction per day. Luckily on AVR microcontrollers, the instructions he needed can execute in just one cycle. That of course meant diving down into assembly code. [Ido] wasn’t an assembly wizard, so to find the instructions, he compiled C code and examined the resulting assembly until he found what he needed. One instruction turns on the LED and the instruction immediately following turns it off again, which normally would make it happen too fast for the human eye to register. But the instruction to turn it on runs on Friday evening and the very next instruction, the one that turns it off, doesn’t run until Saturday evening. Do you feel like you’re in a science fiction story watching time slowed down? Freaky. A few NOPs and the jump for the loop take up the remaining five cycles for the week.

For the source of the clock he chose to use an LDR to detect when the light level dropped at the end of the day. The problem he immediately ran into was that clouds, bird shadows, and so on, also cause drops in the light level. The solution he found was to widen the light and dark range by adding a TLV3702 push-pull output comparator and some resistors. [Ido] gives a detailed explanation of the circuit in the video after the break.

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Faux-AI Clapper Almost Seems to be Listening

When a job can be handled with a microcontroller, [devttys0] likes to buck the trend and build a circuit that requires no coding. Such was the case with this “Clapper”-inspired faux-AI light controller, which ends up being a great lesson in analog design.

The goal was to create a poor man’s JARVIS – something to turn the workshop lights on with a free-form vocal command. Or, at least to make it look that way. This is an all-analog circuit with a couple of op amps and a pair of comparators, so it can’t actually process what’s being said. “Aziz! Light!” will work just as well as any other phrase since the circuit triggers on the amplitude and duration of the spoken command. The AI-lite effect comes from the clever use of the comparators, RC networks to control delays, and what amounts to an AND gate built of discrete MOSFETs. The end result is a circuit that waits until you finish talking to trigger the lights, making it seems like it’s actually analyzing what you say.

We always enjoy [devttys0]’s videos because they’re great lessons in circuit design. From block diagram to finished prototype, everything is presented in logical steps, and there’s always something to learn. His analog circuits that demonstrate math concepts was a real eye-opener for us. And if you want some background on the height of 1980s AI tech that inspired this build, check out the guts of the original “Clapper”.

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The Fastest Rise Time In The West: Making A Truly Quick Pulse Edge

When we are taught about oscillators as newbie engineers, we are shown a variety of waveforms on an oscilloscope or in a textbook. This is a sine wave, they say, this is a sawtooth, this is a square wave, and so on. We’re taught to look at the lines on the screen as idealised, a square wave is truly square, and the transition from low to high voltage and back again is instantaneous.

In most cases this assumption is harmless. If we look into the subject a little deeper we learn that what seemed an instantaneous cliff-face is in fact a very steep slope, but when a circuit does its business in milliseconds there is usually no harm in ignoring a transition time measured in nanoseconds. The glue logic for your Arduino project can take its time.

Sometimes though, the rise time of a logic transition is important. The application that prompted this article was the measurement of oscilloscope bandwidth by looking at how quickly the ‘scope catches up with a pulse that exceeds its bandwidth, for example. When the instrument can happily measure the transition times of all your usual  pulse generators, something out of the ordinary is called for. So it’s worth taking a look at the rise times you’d expect from everyday circuitry, examining a few techniques for generating rise times that are much faster.
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Shop Made Squareness Comparator

[Stefan Gotteswinter] has a thing for precision. So it was no surprise when he confessed frustration that he was unable to check the squareness of the things he made in his shop to the degree his heart desired.

He was looking enviously at the squareness comparator that [Tom Lipton] had made when somone on Instagram posted a photo of the comparator they use every day. [Stefan] loved the design and set out to build one of his own. He copied it shamelessly, made a set of drawings, and got to work.

[Stefan]’s videos are always a trove of good machine shop habits and skills. He always shows how being careful, patient, and doing things the right way can result in really astoundingly precise work out of a home machine shop. The workmanship is beautiful and his knack for machining is apparent throughout. We chuckled at one section where he informed the viewer that you could break a tap on the mill when tapping under power if you bottom out. To avoid this he stopped at a distance he felt was safe: 0.5 mm away.

The construction and finishing complete, [Stefan] shows how to use the comparator at the end of the video, viewable after the break.

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555 Teardown and Analysis

If you are even remotely interested in electronics, chances are the number ‘555’ is immediately recognizable. It is, after all, one of the most popular IC’s ever built, with billions of units sold to date. Designed way back in 1970 by Hans Camenzind, it is still widely available and frequently used for various applications. [Ken Shirriff] does a teardown and analysis of a 555 and gives us a look at the internal structure of this oldie.

A metal can package allowed him to just chop off the top and get access to the die, which was way safer and easier than to etch out the black epoxy of a DIP package. He starts by giving us a quick run down on how the chip works, showing us the two comparators, the output flip-flop and the capacitor discharge circuitry that make up most of the chip. He then puts the die under a metallurgical microscope, and starts identifying the various sections of the chip. Combining pictures of individual elements with cross-sectional diagrams, he identifies the construction of the transistors and resistors, the use of a current mirror to replace bulky resistors, and the differential pair that makes up the comparators.

He wraps it up by providing an interactive map of the die and the schematic, where you can click on various parts and the corresponding component is highlighted along with an explanation of what it does. There’s some interesting trivia about how a redesigned, improved version – the ZSCT1555 – couldn’t survive the popularity and success of the 555. He wraps it up with a useful list of notes and references. While de-capping blog posts are interesting on their own, [Ken] does a great job by giving us a detailed look at the internals.

Thanks [Vikas] for sending in this tip.

Party Ready Mini LED Volume Tower

Audio LED Light Tower

There are many very cool visual effects for music, but the best are the kind you build yourself. [Ben’s] mini LED volume towers adds some nice bling to your music.

[Ben] was inspired to created this project when he saw a variety of awesome stereo LED towers on YouTube (also referred to as VU meters). We have even featured a few VU meters, one very recently. [Ben] goes over every detail, including how to test your circuit (a very important part of any project). The schematic is deceptively simple. It is based on the LM3914 display driver IC, a simple chained comparator circuit is used to control the volume bar display. All you really need is a 3D printer to make the base, and you can build this awesome tower.

See the completed towers in action after the break. What next? It would be cool to see a larger tower that displays frequency magnitude!

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Halloween Links: October 30th, 2013


Happy Halloween from everyone at Hackaday! To help you enjoy the holiday here are a few festive links:

[Mike Kohn] whipped up a set of motion tracking eyeballs to make his decor extra creepy.

There’s not much to this jet-pack costume but the results are pretty amusing.

The eyes on [Tim Butler’s] skeleton prop don’t follow you around the room, but they do use a PIR sensor to light up the skull.

Speaking of skulls, [Tom] is using some real skulls as decorations. He also added lights where the eyeballs should be, but he is using a photoresistor and comparator to turn on some LEDs.

[Clark] built a Mecha Robot Warrior costume for his son. With all of those LED strips we think he’ll be pretty safe when crossing the street!

And finally, [Jesse] added a lot to his prop in order to produce a Sinister Joker. That’s Joker-as-in-cards and not as in Batman. It’s got an IR distance sensor as a trigger, with a motor to move the wrist, lights for the eyes, and a sound shield to give it a disturbing voice.