Capacitive Sensing Tutorial

September 26, 2011 by Brian Benchoff 13 Comments

[Bertho]’s submission for the 74xx logic contest is really impressive. He designed a capacitive sensing touchpad using only 74xx and 40xx logic chips. We’re impressed with the build and his writeup is one of the best resources we’ve ever seen for capacitive sensing.

There are two ways to go about designing a capacitive touchpad. The first option is put a voltage through an RC circuit. Measure the voltage-time curve, and you have a measure of the capacitance of the circuit. The second method is setting up an RC circuit to change polarity after a threshold for C has been reached. Microprocessors only use one of these methods (AVR uses the first, PIC uses the second), but [Bertho] decided to implement both methods for unknown reasons we still respect.

The circuit [Bertho] designed has a 30MHz clock using only 74xx logic chips, an amazing feat in itself. An 8×8 channel panel was fabricated and the whole build connects to a computer over RS-232.

The finished build is good enough has 64 points of resolution and is able to detect proximity very well. The touchpad is even able to recognize when a pen is placed on the panel. Check out the video after the break for the walk through and demo of this amazing build.

Continue reading “Capacitive Sensing Tutorial” →

Record Sound Without A Microcontroller

September 15, 2011 by Brian Benchoff 14 Comments

For his A-level electronic course work, [Andrew] decided to build a digital sound recorder that doesn’t use a microcontroller.

[Andrew]’s build captures audio from an on board microphone at 8000 samples/second. The audio is digitized into 8-bit sound data and sent to an SRAM. The recording and playback functions are controlled entirely by 4000-series logic chips. He admits the sound quality is pretty poor; this is mostly due to the 8kHz sample rate. In some circles, though, a terrible sample rate is seen as being pretty cool so we’re not going to say [Andrew]’s build is useless.

There’s some pretty smart design choices in [Andrew]’s build, like a cut off filter on the microphone set at 4000 Hz (the Nyquist frequency of his system). For the recording medium, he used an SRAM that can hold about half a megabyte of data. At 8000 samples/second, [Andrew]’s build can store a little more than 60 seconds of audio. The build may not be a logic chip computer, but there’s not any question in our mind that [Andrew] learned something. Check out [Andrew]’s 66-page coursework report here (PDF warning).

Recovering Data For A Homemade Cray

September 8, 2011 by Brian Benchoff 41 Comments

In our hubris, we pat ourselves on the back when we’re able to pull data off our old SCSI drives. [Chris Fenton]’s attempt to get an OS for a homebrew Cray-1 puts us rightfully to shame.

Last year we saw [Chris]’ fully functional 1/10th scale Cray-1 supercomputer built around FPGA. While the reproduction was nearly cycle-accurate, [Chris] hasn’t had an opportunity to test out his system because of the lack of available Cray software. A former Cray employee heard of his plight and loaned an 80 Megabyte CDC 9877 disk pack to in the hope of getting some system software.

[Chris] acquired a monstrous 100 pound disk drive to read the disk pack, but after 30 years in storage a lot of electrical problems cropped up. Since reading the drive digitally proved to be an exercise in futility, [Chris] hit upon the idea of taking analog data straight from the read head. This left him with a magnetic image of the disk pack that was ready for some data analysis.

After the disk image was put up on the Internet, the very talented [Yngve AAdlandsvik] figured out the data, header, and error correction formats and sent [Chris] a Python script to tease bits from the analog image. While no one is quite sure what is on the disk pack provided by the Cray employee, [Chris] is remarkably close to bringing the Cray-1 OS back from the dead. There’s also a great research report [Chris] wrote as penance for access to the CDC disk drive. Any Hack A Day readers feel like looking over the data and possibly giving [Chris] a hand?

Highway Based Soundtrack Recordings

September 1, 2011 by Brian Benchoff 21 Comments

[Urpo Lankinen] has a father who is a huge movie buff, and once you care deeply about something it begins appearing everywhere you look. While driving on a back-country road one day, [Urpo]’s dad noticed that the shadows of the trees on the road looked like an optical film soundtrack, so it was up to the son to make it happen.

Early sound-on-film technologies like the RCA Photophone, and Movietone recorded audio onto the film stock with a variable area exposure. This exposure corresponds to the waveform of the audio signal. [Urpo] figured that his small digital video camera served the same purpose as the audio sensors inside the projector, so he put a piece of tissue paper over the lens and wound up with a video that was just frames of gray.

[Urpo] built an app in Processing that averages the pixels in each frame of the video. Of course, recording at 30 frames/second won’t produce any audio this way, so he modulated a triangle wave with this data in Audacity. In the end it really doesn’t sound like much, but it’s great to see such a geeky build.

We’d love to post the video after a break but [Urpo] doesn’t believe in YouTube embeds. We’ll honor his wishes, so you can check out the video here.

High Voltage Hacks: Transmute The Elements In Your Garage

August 27, 2011 by Brian Benchoff 13 Comments

The magnum opus of alchemy was the Philosopher’s stone, a substance that was able to turn common metals into gold. Unlike alchemists, [Carl Willis] might not be poisoning himself in a multitude of ways, but he did build a Farnsworth fusor that’s capable of turning Hydrogen into Helium.

To fuse Hydrogen in his device, [Carl] first evacuates a vacuum chamber. Deuterium (Hydrogen with an added neutron) is injected into the chamber, and a spherical cathode made of Tungsten is charged to 75 kV. The deuterium gas is heated and confined by the cathode and fuses into Helium. The electrostatic confinement of the plasma isn’t very much different from some old CRT tubes. This isn’t a coincidence – both the fusor and CRTs were invented by the same man.

While no fusion experiments – including some billion dollar experiments – have ever produced a net energy gain, this doesn’t mean it’s not an impressive engineering feat. If you’d like to try your hand at building your own fusor, drop by the surprisingly active research forum. There’s a lot of really good projects to look through over there.

High Voltage Hacks: Shrinking Coins

August 20, 2011 by Brian Benchoff 22 Comments

The anthem for the Great Recession might be something along the lines of, “That we’re gonna do it anyway, even if doesn’t pay.” Some men just want to watch the world burn, so Hackerbot Labs posted a great walkthrough about shrinking coins and in the process making our pocket change worth just a little bit more.

Their build pushes 15,000 Joules (from a 10kV 300μF cap) through a coil of wire wrapped around a coin. This creates a magnetic field in the coil and the coin. These two fields repel each other, and there’s only one way that it can end: the coin shrinks and the coil of wire explodes. The team at Hackerbot Labs linked to a great theory of operations that ~~does a great job explaining the physics~~ has some awesome pictures.

During our research, we saw a few questions about the legality of altering currency. According to the U.S. Code, shrinking coins only illegal if it’s done fraudulently, like shrinking a penny down to the size of a dime to fool a pay phone or vending machine. Check out a video of the Hackerbot Labs setup putting as much energy as 100 heart defibrillators into a coin after the break.

Continue reading “High Voltage Hacks: Shrinking Coins” →

Adding Wireless Controls To Vintage Stereo Equipment

August 19, 2011 by Mike Nathan 11 Comments

marantz_wifi_remote_control

[Jean] was shopping around for a vintage stereo receiver, and happened upon a broken, but repairable Marantz 4240. After getting things back to working order, he thought it would be great if he could use his iPhone to remotely control the unit (PDF Writeup, Schematics and Code).

He scrounged around for parts, and after locating a PIC and a handful of parts from old copiers and printers, he got down to business. He etched some custom boards to house electronic bits, then strapped motors to the volume and source selection knobs. He also rigged up the push button power switch on the receiver, using a small servo and a bit of string.

Now, he can control everything using his iPhone, which communicates with the stereo over WiFi. While the power, volume knob, and input selector can be triggered remotely, he still has the ability to tweak any of these items manually if desired.

We think that this is a great way to add modern amenities to vintage electronics, without ruining the aesthetics of the components. Don’t take our word for it though, check out the video demonstrations [Jean] but together after the jump.

Continue reading “Adding Wireless Controls To Vintage Stereo Equipment” →