Conjuring Capacitive Touch Sensors from Paper and Aluminum Foil

Stumbling around YouTube, we found what has to be the lowest-tech method of producing a touchpad to make a capacitive touch keyboard, and we just had to share it with you. If you’re afraid of spoilers, skip down to the video below the break now.

[James Eckert] got his hands on a Freescale MPR121 capacitive touch sensor. The chip in question speaks I2C and senses up to twelve simultaneous capacitive sense electrodes; break-out boards are available in all of the usual places. It’s a sweet little part.

So [James] had to make a twelve-key capacitive keyboard on the quick. He printed out a key template on paper — something that he does often in his woodwork — and spray-glued aluminum foil on the back side. The video doesn’t say how many hours he spent with the razor blade tracing it all out, but the result is a paper, foil, and packing tape keyboard that seems to work just fine.

A pin-header was affixed to the foil with conductive paint and more tape. If you’ve ever tried soldering directly to aluminum foil, you’d know why. (And if you’ve got any other good tips for connecting electrically to aluminum foil, we’d love to hear them.)

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Easy Power Supply Mod Takes Control

Inexpensive bench top power supplies are great for the home hobbyist, featuring wide voltage range and current limiting for a low price. What’s not to love? The controls; most have a single-turn pot that is typically very fidgety, especially at low voltage.

The solution is to replace the factory pots with nice wire-wound 10 turn units in order to gain 10x the precision. Of course nothing is ever drop in, the new pots didn’t fit the old holes, but that is nothing a few moments with a drill can’t fix. Also the original knobs no longer fit, but that’s just an opportunity for a knob upgrade.

The end result is still a power supply with fidgety controls, but instead of holding your breath, tippy tapping knobs to get within 100mV of your target, you can dial right in to within 10mV of your target. That makes life much easier, especially on low voltage projects that may not have power regulation quite yet.

Join us after the break for a video with all the info.

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KiCad 4.0 is Released

If you’re a KiCad user, as many of us here at Hackaday are, you’ll be elated to hear that KiCad 4.0 has just been released! If you’re not yet a KiCad user, or if you’ve given it a shot in the past, now’s probably a good time to give it a try. (Or maybe wait until the inevitable 4.0.1 bugfix version comes out.)

If you’ve been using the old “stable” version of KiCad (from May 2013!), you’ve got a lot of catching-up to do.

The official part footprint libraries changed their format sometime in 2014, and are all now hosted on GitHub in separate “.pretty” folders for modularity and ease of updating. Unfortunately, this means that you’ll need to be a little careful with your projects until you’ve switched all the parts over. The blow is softened by a “component rescue helper” but you’re still going to need to be careful if you’re still using old schematics with the new version.

The most interesting change, from a basic PCB-layout perspective, is the push-and-shove router. We’re looking for a new demo video online, but this one from earlier this year will have to do for now. We’ve been using various “unstable” builds of KiCad for the last two years just because of this feature, so it’s awesome to see it out in an actual release. The push-and-shove router still has some quirks, and doesn’t have all the functionality of the original routers, though, so we often find ourselves switching back and forth. But when you need the push-and-shove feature, it’s awesome.

If you’re doing a board where timing is critical, KiCad 4.0 has a bunch of differential trace and trace-length tuning options that are something far beyond the last release. The 3D board rendering has also greatly improved.

Indeed, there are so many improvements that have been made over the last two and a half years, that everybody we know has been using the nightly development builds of KiCad instead of the old stable version. If you’ve been doing the same, version 4.0 may not have all that much new for you. But if you’re new to KiCad, now’s a great time to jump in.

We’ve covered KiCad hacks before, and have another article on KiCad add-on utilities in the pipeline as we write this. For beginners, [Chris Gammell]’s tutorial video series is still relevant, and is a must-watch.

Arduino Powered Knife-Wielding Tentacle will Leave You in Stitches

Writing articles for Hackaday, we see funny projects, and we see dangerous projects. It’s rare to find a project which combines the two. This one somehow manages to pull it off. [Outaspaceman] is familiar with LittleBits, but he’s just starting to learn Arduino programming. He completed the blink tutorial, but blinking an LED just wasn’t enough fanfare for the success of his first Arduino program. He connected the Arduino Mega’s LED output to a pair of LittleBits which then switch a servo between two positions. A bare servo wouldn’t be much fun, so [Outaspaceman] connected a tentacle and a small Swiss army knife. Yes, a knife.

The tentacle in question is designed to be a finger puppet. There’s something about a tentacle waving a knife around that is so hilarious and absurd that we couldn’t help but laugh. We’re not alone apparently, as this video has gone viral with over 1 million views. It’s almost like a violent revenge of the most useless machine. For the technically curious, the tentacle’s seemingly random motion is analogous to that of the double pendulum.

Our readers will be happy to know that [Outaspaceman] has made it to the Arduino servo tutorial, and is now controlling the servo directly, no LittleBits needed. We just hope he has a good way to turn his creation off – without the need for stitches.

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Uses for Quantum Entanglement with Shanni Prutchi

For those of you that weren’t at the Hackaday SuperConference, it started off with a pretty intense talk that could have been tough for anyone to follow. However, [Shanni Prutchi] presented her talk on quantum entanglement of photons in a way that is both approachable, and leaves you with plenty of hints for further study. Check it out in the video below, and join us after the break for a rundown of what she covered in her presentation.

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The Grid Dip Meter: Forgotten Instrument

It used to be a major rite of passage for a hardware hacker to acquire an oscilloscope. Until recently, new instruments were rarely in normal people’s budgets, so you probably made do with a used scope. Now, there are lots of inexpensive options, especially if you include low-end PC scopes and “scope meters.” Digital meters are also now inexpensive (often free at some major stores), along with signal generators, frequency counters, and even logic analyzers.

But there is one piece of test equipment you don’t see as often as you used to and its a shame, because it is a very versatile piece of kit. Admittedly, if you aren’t doing wireless work, it might not be high on your wish list, but if you do anything with RF, it is not only a versatile tool, but a good value, too. What’s it called? That depends. Historically, they went by the name “Grid Dip Oscillator” or GDO. Sometimes you’d hear it called a “Grid Dip Meter” instead. However, modern versions don’t have tubes (and, thus, no grid) so sometimes you hear them now called dip meters or maybe just dippers.

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1Wamp, An Open Hardware Guitar Amplifier

The folks at [ElectroSmash] recently released 1Wamp – a one watt, open hardware, Guitar amplifier packed with features. It consists of a JFET based pre-amplifier, a Big Muff Pi a.k.a BMP based Tone control and an LM386 power amplifier. The dual JFET pre-amp provides tube-like sound, the BMP provides a nice tonal range while the LM386 can drive various types of output’s ranging from headphones to speaker cabinets.

1Wamp had controls for Tone, Volume and Gain, a Speaker/Cabinet output, a headphone output with an integrated attenuator switch and an aux. input. The aux. input is handy as it adds any line level input signal to the guitar sound, allowing you to practice with metronome or MP3 backing tracks or drum bases. It runs off either a 9V battery or can be powered via an external power source. [ElectroSmash] have released all the native KiCad design files. If you’d like a quick look at the design, check out the Schematic PDF and the Bill of Materials. There’s also a handy assembly manual [PDF] that shows how to build it in five easy steps.

Their blog post provides extremely detailed circuit analysis of every part of the design, starting from the power supply filter to remove mains “hum” all the way through to PCB layout considerations for noise reduction. Oscilloscope screen shots provide signal analysis showing bias points and signal levels throughout the circuit. The choice of value for every component is explained, along with the consequences of changing those values. This makes it easy to customise the 1Wamp to suit individual tastes. We also noticed SPICE models for the recommended and alternative JFET transistors, in case you need to customise the design by changing component values.

There’s also a lot of audio amplifier trivia, references and links shared in their post. This includes a detailed analysis of the LM386 op-amp. Want to add some bling to your 1Wamp build? There are a lot of handy tips on how to add cool LED lighting to the amplifier if it is mounted in a standard metal enclosure. However, the PCB has some really nice graphics, so an acrylic-sandwich-type enclosures look best. Check out the video that walks through the features of the 1Wamp and shows off its performance. And while on the subject of Audio electronics, here’s one of their earlier projects – an open source Arduino guitar pedal.

Documentation to this level proves several things, most notably a love for this design and deep consideration for those who will use and modify this amplifier. It’s a great pattern to follow with your own Open Source designs.

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