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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Negative Resistance: It Shouldn’t Make Sense!

When you leaf through a basic electronics textbook, you’ll find chapters describing in detail the operation of the various components. Resistors, capacitors, inductors, and semiconductors. The latter chapter will talk about P and N type regions, introduce us to the diode, and then deal with the transistor: its basic operation, how to bias it, and the like.

A tunnel diode amplifier circuit. Chetvorno [CC0]
Particularly if your textbook is a little older, you may find a short section talking about the tunnel diode. There will be an odd-looking circuit that seems to make no sense at all, an amplifier formed from just a forward-biased diode and a couple of resistors. This logic-defying circuit you are told works due to the tunnel diode being of a class of devices having a negative resistance, though in the absence of readily available devices for experimentation it can be difficult to wrap your head around.

We’re all used to conventional resistors, devices that follow Ohm’s Law. When you apply a voltage to a resistor, a current flows through it, and when the voltage is increased, so does the current. Thus if you use a positive resistance device, say a normal resistor, in both the top and the bottom halves of a potential divider, varying the voltage fed into the top of the divider results in the resistor behaving as you’d expect, and the voltage across it increases.

In a negative resistance device the opposite is the case: increasing the voltage across it results in decreasing current flowing through it. When a large enough negative resistance device is used in the lower half of a resistive divider, it reduces the overall current flowing through the divider when the input voltage increases. With less current flowing across the top resistor, more voltage is present at the output. This makes the negative resistor divider into an amplifier.

The tunnel diodes we mentioned above are probably the best known devices that exhibit negative resistance, and there was a time in the early 1960s before transistors gained extra performance that they seemed to represent the future in electronics. But they aren’t the only devices with a negative resistance curve, indeed aside from other semiconductors such as Gunn diodes you can find negative resistance in some surprising places. Electrical arcs, for example, or fluorescent lighting tubes.

A typical negative resistance I-V curve. Chetvorno [CC0]
The negative resistance property of electric arcs in particular produced a fascinating device from the early twentieth century. The first radio transmitters used an electric arc to generate their RF, but were extremely inefficient and wideband, causing interference. A refinement treated the spark not as the source of the RF but as the negative resistance element alongside a tuned circuit in an oscillator, These devices could generate single frequencies at extremely high power, and thus became popular as high-powered transmitters alongside those using high-frequency alternators until the advent of higher powered tube-based transmitters around the First World War.

It’s unlikely that you will encounter a tunnel diode or other similar electronic component outside the realm of very specialist surplus parts suppliers. We’ve featured them only rarely, and then they are usually surplus devices from the 1960s. But understanding something of how they operate in a circuit should be part of the general knowledge of anyone with an interest in electronics, and is thus worth taking a moment to look at.

1N3716 tunnel diode header image: Caliston [Public domain].

Fix-a-Brick: Fighting the Nexus 5X Bootloop

Oh Nexus 5X, how could you? I found my beloved device was holding my files hostage having succumbed to the dreaded bootloop. But hey, we’re hackers, right? I’ve got this.

It was a long, quiet Friday afternoon when I noticed my Nexus 5X was asking to install yet another update. Usually I leave these things for a few days before eventually giving in, but at some point I must have accidentally clicked to accept the update. Later that day I found my phone mid-way through the update and figured I’d just wait it out. No dice — an hour later, my phone was off. Powering up led to it repeatedly falling back to the “Google” screen; the dreaded bootloop.

Stages of Grief

I kept my phone on me for the rest of the night’s jubilant activities, playing with it from time to time, but alas, nothing would make it budge. The problem was, my Nexus still had a full day’s video shoot locked away on its internal flash that I needed rather badly. I had to fix the phone, at least long enough to recover my files. This is the story of my attempt to debrick my Nexus 5X.

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Light-Painting Robot Turns any Floor into Art

Is [SpongeBob SquarePants] art? Opinions will differ, but there’s little doubt about how cool it is to render a pixel-mapped time-lapse portrait of Bikini Bottom’s most famous native son with a roving light painting robot.

Inspired by the recent trend of long exposure pictures of light-adorned Roombas in darkened rooms, [Hacker House] decided to go one step beyond and make a lighted robot with less random navigational tendencies. A 3D-printed frame and wheels carries a pair of steppers and a Raspberry Pi. An 8×8 Neopixel matrix on top provides the light. The software is capable of rendering both simple vector images and rastering across a large surface to produce full-color images. You’ll notice the careful coordination between movement and light in the video below, as well as the impressive turn-on-a-dime performance of the rover, both of which make the images produced so precise.

We’ve covered a lot of light-painting videos before, including jiggering a 3D-printer and using a hanging plotter to paint. But we haven’t seen a light-painter with an essentially unlimited canvas before. We’d also love to see what two or more of these little fellows could accomplish working together.

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Zelda and the Ocarina of Things

Voice recognition is this year’s model for home automation, but aside from feeling like you’re onboard the Aries 1b arguing with HAL 9000, it just doesn’t do it for our geeky selves. So what’s even geekier? How about carrying around an ocarina in your pocket so that you can get a Raspberry Pi to unlock the door for you? (YouTube video, embedded below.) Yeah, that’ll do.

[Sufficiently Advanced]’s video gets us 90% of the way toward replicating this build. There’s a tube with a microphone and a Raspberry Pi inside. There are a bunch of ESP8266-powered gadgets scattered around the house that take care of such things as turning on and off the heater, watering plants, and even pressing a (spare) car remote with a servo.

We’d love to know what pitch- or song-recognition software the Raspberry Pi is running. We’ve wanted to implement a whistling-based home automation interface since seeing the whistled. We can hold a tune just fine, but we don’t always start out on the same exact pitch, which is a degree of freedom that [Sufficiently Advanced]’s system doesn’t have to worry about, assuming it only responds to one ocarina.

If you’re questioning the security of locking and unlocking your actual apartment by playing “Zelda’s Lullaby” from outside your window, you either overestimate the common thief or you just don’t get the joke. The use case of calling (and hopefully finding) a cell phone is reason enough for us to carry a bulky ocarina around everywhere we go!

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Hanging 3D Printer Uses Entire Room As Print Bed

There are many things people do with spare rooms. Some make guest rooms, others make baby rooms, while a few even make craft rooms. What do hackers do with spare rooms? Turn them into giant 3D printers of course. [Torbjørn Ludvigsen] is a physics major out of Umea University in Sweden, and built the Hangprinter for only $250 in parts. It follows the RepRap tradition of being completely open source and made mostly from parts that it can print.

The printer is fully functional, proven by printing a five-foot tall model of the Tower of Babel. [Torbjorn] hopes to improve the printer to allow it to print pieces of furniture and other larger household items.

[Torbjorn] hopes that 3D printing will not go down the same road that 2D printing went, where the printers are designed to break after so many prints. Open source is the key to stopping such machines from getting out there.

Thanks to [Jeremy Southard] for the tip!

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2017 Hackaday Prize Begins Right Now

Today the 2017 Hackaday Prize begins!

This is Hackaday’s global engineering initiative that encourages people to direct their skill and energy to make the world a better place. We call it the Hackaday Prize, but it’s far more than that. Join a community of talented people who enrich their own lives by seeking out new challenges and new technologies, then pioneers a way to combine them to Build Something that Matters. Show us your build by starting a Hackaday.io project page and enter today!

You Have Every Reason to Get Involved

The Hackaday Prize truly has something for everyone. Making the world a better place doesn’t end with a grand prize for a single build. Just by talking about your ideas and sharing your excitement you become the inspiration for this and every successive generation of problem solvers. But yes, there are prizes — a lot of prizes — and they’re spectacular.

We have over $250,000 in cash going out to hundreds of entries this year. The Grand Prize of $50,000 is joined once again this year by the Best Product Prize of $30,000. Four other entries will place second through fifth and receive $20k, $15k, $10k, and $5k respectively.

But the breadth of entries is too great to stop at that. We’ll select 120 projects as finalists and award each $1000. You can even get in on Seed Funding starting right away. We’re saving those details for the end of this announcement.

How Do I Build Something that Matters?

Whoa, all this talk of prizes, but you want to know what kind of hardware will be a hit for the Hackaday Prize? Here’s what you need to know: you can enter your project at any time from now until October 16th. But the exact time that you enter matters.

Your best bet is to get started right away. The first challenge of the Hackaday Prize is: Design Your Concept. Every great build starts with a plan and this is the time to show us what you got. The key is to consider if the project benefits society in some way. Show us how, document your build plan, and you can be one of the first twenty finalists to receive $1k cash and move on to compete for the big prizes.

We’ll have four more challenges that focus on different types of entries. You only need to enter one challenge, but you may choose to enter (and win) as many of the five challenges as you wish. We’ll be looking for connected devices that don’t suck Internet of Useful Things during the IuT ! IoT challenge. After that, it’s on to all things mobile with the Wheels, Wings, and Walkers challenge. Assistive Technology challenges you to make the world a better place for the physically or mentally challenged and aging or sick people of the world. And finally, a Hackaday favorite closes the challenge rounds with Anything Goes — as long as it clearly benefits society. Each of these five challenges will yield twenty finalists who receive $1000. That’s $100k!

The Return of Best Product

Two years ago we tried something new by adding the Best Product Prize to the mix and it was an enormous hit. We’re happy to be able to bring it back again this year.

There is a difficult path from a working prototype to a product ready for its audience. As hardware development is unlocked for an ever wider engineering community, we want to see the path made wider so that the journey becomes easier. Best Product is designed to do just that.

Any Hackaday Prize entry may also choose to compete and be named the Best Product (receiving much deserved recognition as well as the addition $30k prize). You need to submit your entry no later than July 24th, which includes full documentation of the project as well as a bill of materials used in the build. We’ll select twenty finalists (sending $1k to each) who will then need to deliver three working beta test units for the final judging round of the Best Product.

How Can We Pick the Top Entries?

One amazing part of the Hackaday Prize family are the world-renowned experts who donate their time and talent as Judges. They are just as eager as everyone else to see all of this creative energy focused on solving the problems facing our civilization.

Learn more about all of these amazing people on the Hackaday Prize page.

One Last Thing: Seed Funding

When realized to their full potential, design concepts should knock the socks off of anyone who reads through them. Because of this we have one more thing in store for you during the first challenge which starts right now.

Entries with the most likes at the end of the first round will split $4,000. Each time someone on Hackaday.io “likes” your project it will move a bit higher on the leaderboard found on the Hackaday Prize page. The top projects will receive $1 for each like, with a max of $200 per entry so that at least twenty will win (but likely many more).

This seed funding is a little push to help offset the cost of building prototypes. But it really comes down to your decision to make the time and to make a difference. Enter your project in the Hackaday Prize now.