Embed With Elliot: The Static Keyword You Don’t Fully Understand

August 4, 2015 by 70 Comments

One of our favorite nuances of the C programming language (and its descendants) is the static keyword. It’s a little bit tricky to get your head around at first, because it can have two (or three) subtly different applications in different situations, but it’s so useful that it’s worth taking the time to get to know.

And before you Arduino users out there click away, static variables solve a couple of common problems that occur in Arduino programming. Take this test to see if it matters to you: will the following Arduino snippet ever print out “Hello World”?

void loop()
{
	int count=0;
	count = count + 1;
	if (count > 10) {
		Serial.println("Hello World");
	}
}

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Engineers Create Super-Hard Whack-a-Mole

August 4, 2015 by 6 Comments

Is your latest project driving you mad? Are you subject to occasional fits of rage? This project might help: for a class called elecanisms at Olin College, [Forrest] and a team of three other students made a whack-a-mole arcade game that lets you vent your rage on a helpless furry animal by whacking it with a large hammer. He built most of it from scratch, creating his own solenoid driver and LED sensor board. However, there is a twist in here that gives the moles a fighting chance: there is an accelerometer built into the hammer that lets them know that your heavy hammer of doom is approaching.

Will they escape before your righteous wrath descends upon them? That depends on how you decide to set it up, and how merciful you want to be. The build even includes a coin-operated pay-to-play slot. They kept the cost low at a penny, but this is just begging to be installed at the local pub to rake in those quarters.

This course has been the source of a few projects that we have featured before on Hackaday, including the Confectionary Canon, which tracks your face and fires marshmallows right into your gaping maw.

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Clocking (or Overclocking) An AVR

August 4, 2015 by 26 Comments

Some guys build hot rods in their garage. Some guys overclock their PCs to ridiculously high clock frequencies (ahem… we might occasionally be guilty of this). [Nerd Ralph] decided to push an ATTiny13a to over twice its rated frequency.

It didn’t seem very difficult. [Ralph] used a 44.2 MHz can oscillator and set the device to use an external clock. He tested with a bit-banged UART and it worked as long as he kept the supply voltage at 5V. He also talks about some other ways to hack out an external oscillator to get higher than stock frequencies.

We wouldn’t suggest depending on an overclock on an important or commercial project. There could be long term effects or subtle issues. Naturally, you can’t depend on every part working the same at an untested frequency, either. But we’d be really interested in hear how you would test this overclocked chip for adverse effects.

Now, if you are just doing this for sport, a little liquid nitrogen will push your Arduino to 65 MHz (see the video after the break). We’ve covered pushing a 20MHz AVR to 30MHz before, but that’s a little less ratio than [Ralph] achieved.

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Hackaday Prize Entry: Wearable Electrodermal Activity Monitor

August 3, 2015 by 1 Comment

Electrodermal activity, or galvanic skin response has a lot of practical applications. Everything from research into emotional states to significantly more off-the-wall applications like the E-meter use electrodermal activity. For his Hackaday Prize entry, [qquuiinn] is building a wearable biofeedback wristband that measures galvanic skin response that is perfect for treating anxiety or stress disorders by serving as a simple and convenient wearable device.

Detecting electrodermal activity has been within the capability of anyone with an ohmmeter for over a hundred years. [quin²] is doing something a little more complex than the most primitive modern means of measuring galvanic skin response and using a dual op-amp to sense the tiny changes in skin resistance. This data is fed into an ATMega328 which sends it out to a tiny LED display in the shape of an ‘x’.

Reading electrodermal activity is easy, but doing it reliably in a wearable device is not. There are issues with the skin contacts to work though, issues with the amplifier, and putting the whole thing in a convenient package. [qquuiinn] asked the community about these problems in group discussion on the hacker channel and got a lot of really good advice. That’s a great example of what a project on hackaday.io can do, and a great project for the Hackaday Prize.

The 2015 Hackaday Prize is sponsored by:

Caption CERN Contest – All Good Things…

August 3, 2015 by 6 Comments

Week 25 of the Caption CERN Contest is complete. Thanks to all the entrants who tried to figure out exactly what is going on with this scientist and his strange box. We’re still just as confused (and amused) as you are. He definitely is focused on the box and whatever is in there.

So, without further adieu, here are the winners of this week’s contest:

The Funnies:

  • “On the slim chance my invention does not go down in history. I hope no one makes a Schrodinger’s cat joke about it.” – [masterdurr]
  • “Step one, you cut a hole in the box” – [FuzzyNegguts]
  • “here is a rare shot of CERNs artificial heart prototype. Due to its size, it was only installed in whales. And badgers. I don’t know how, but somehow badgers.” – [jakewisher125]

This week’s winner is [Jack Laidlaw] with  “At Cern you have to be careful when having fun with the new guy, John was sent for a bucket of steam and only reappeared 6 months later with this contraption.” Jack is a web designer based in Scotland. He’s an avid fan of electronics, and is going to be getting a hands on course with his new Teensy 3.1 from The Hackaday Store!

A bit of a break

After 25 great weeks of the Caption CERN Contest, it’s time to take a bit of a break. The Hackaday Prize competition is really heating up, along with plenty of other work here at Hackaday HQ. I’ve said it each week, but I have to give one more big thank you to all the folks who have entered and made this a great contest. It’s been a pleasure to read the captions every week and to award the prizes to all the top captions. The science and fun don’t end here though – There are plenty of images in CERN’s archives waiting to be discovered. Take some time and browse through. You won’t regret it!

Finally, I’d just like to say don’t forget to document your own work, and take notes on what each image contains. Be it on Hackaday.io, on Github, or even on your own drive. Otherwise you might see your own hacks in the next incarnation of the Caption CERN Contest!

Building A Battery From Molten Salt

August 3, 2015 by 38 Comments

During World War II a scientist named Georg Otto Erb developed the molten salt battery for use in military applications. The war ended before Erb’s batteries found any real use, but British Intelligence wrote a report about the technology and the United States adopted the technology for artillery fuses.

Molten salt batteries have two main advantages. First, you can store them for a long time (50 years or more) with no problems. Once the salt melts (usually from a pyrotechnic charge), the battery can produce a lot of energy for a relatively short period of time thanks to the high ionic conductivity of the electrolyte (about three times that of sulfuric acid).

[OrbitalDesigns] couldn’t find a DIY version of a molten salt battery so he decided to make one himself. Although he didn’t get the amount of power you’d find in a commercial design, it did provide 1.6V and enough power to light an LED.

The electrolyte was a mixture of potassium chloride and lithium chloride and melts at about 350 to 400 degrees Celsius. He used nickel and magnesium for electrodes. Potassium chloride is used as a salt substitute, so it isn’t dangerous to handle (at least, no more dangerous than anything else heated to 400 degrees Celsius). The lithium compound, however, is slightly toxic (even though it was briefly sold as a salt substitute, also). If you try to replicate the battery, be sure you read the MSDS for all the materials.

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Dissolve Steel Drill Bits In Alum From The Grocery

August 3, 2015 by 37 Comments

Breaking a stud or a bolt is a pretty common shop catastrophe, but one for which a fair number of solutions exist. Drill it out, shoot in an extractor, or if you’re lucky, clamp on some Vise-Grips and hope for the best. But when a drill bit breaks off flush in a hole, there aren’t a lot of options, especially for a small bit. If the stars align, though, you may follow this video guide to dissolve the drill bit and save the part.

Looks like [Adam Prince] lucked out with his broken bit, which he was using to drill the hole for a pin in a small custom brass hinge. It turns out that a hot solution of alum (ammonium aluminum sulfate), which is available in the spice rack of your local supermarket, will dissolve the steel drill bit without reacting with the brass. Aluminum is said to be resistant to the alum as well, but if your busted bit is buried in steel, you’re out of luck with this shop tip.

We’re a bit disappointed that [Adam]’s video ends somewhat abruptly and before showing us the end result. But a little Googling around reveals that this chemical technique is fairly well-known among a group that would frequently break bits in brass – clockmakers. It remains to be seen how well it would work for larger drill bits, but the clocksmiths seem to have had success with their tiny drills and broaches.

As for the non-dissolved remains of the broken bit, why not try your hand at knife making?