Amplifying the Body’s Own Electricity

Measuring the body’s electrical signals is a neat trick… if you can get your equipment dialed in enough to establish dependable measurements. The technique is called Surface ElectroMyography (SEMG) though you’ll hear many call this ECG. They’re essentially the same technology; the Electro CardioGraph instruments monitor the activity of the heart while SEMG Instruments monitor electrical signals used to control other muscles. Both types of hardware amount to an instrumentation type amplifier and some form of I/O or display.

This topic has been in my back pocket for many months now. Back in May we Hackaday’ites descended on New York City for the Disrupt NY Hackathon event. We arrived a day or so early so that we might better peruse the Korean BBQ joints and check out the other electronics that NY has to offer. On Saturday we gathered around, each shouting out the size of his or her t-shirt preference as we covered up our black Hackaday logo tees with maroon maroon ones (sporting the Hackaday logo of course) for a 24-hour craze of hardware hacking.

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There were two individuals at our tables who were both hacking away on hardware to measure the electrical field produced by the body’s muscles in some form or another. The electrical signals measured from the skin are small, and need careful consideration to measure the signal despite the noise. This is a fun experiment that lets you work with both Instrumentation Amplifiers and OpAmps to achieve a usable signal from the movement of your body.

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TI Releases New Edition Analog Engineer’s Pocket Reference

We aren’t sure that a PDF with 100 pages in it qualifies as a pocket reference, but TI’s Analog Engineer’s Pocket Reference is certainly a good read. You do have to register with TI (use a disposable address if you are too paranoid to do that), but the free download is well worth the effort. The document’s been around for awhile, but TI recently released a new 4th edition.

The first few pages might underwhelm you. You probably know the standard decimal prefixes and are more likely to ask Google to convert circular mils to square millimeters, for example. The second part, though, gets more into electronics. There’s standard values for resistors and quick reminders about the difference between X7R and Y5V ceramic in capacitors, for example.

Things get progressively more interesting, covering measurements and phase shifts, and then amplifiers. The little circuits are pithy but cover the bases including things like frequency response.

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Old School Analog Meters Tell you the Weather

A home weather station is great geek street cred. Buying a commercially available station will get you all the bells and whistles, but the look tends to the utilitarian. And then there’s the trouble of placing the sensor array somewhere. To solve both problems, [GradyHillhouse] built this unique weather station with analog meters.

Based on a Particle Photon pulling weather data from the forecast.io API, values for temperature, pressure and the like are sent to analog IO pins. Each pin has a meter with a trimmer pot for calibration and a custom printed label. There’s also a digital output that goes high when a severe weather alert is posted; that drives an LED behind the bezel of one of the meters. Everything is mounted in a walnut plaque which makes for a nice presentation. The video after the break details the build.

As you can imagine, we’ve featured lots of weather stations before. Some display their data on a screen, some in more unique ways. But we really like the old school look and simplicity of this project.

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Tape Loop Echo Made With an Actual Tape Loop

A lot of digital processes are named after an old analog device that they’ve since replaced. It’s not uncommon to “tape” a show nowadays, for example, even though the recording work is actually done by a digital video recorder. Sometimes, though, the old analog devices have a certain je ne sais quoi that is desirable even in today’s digital world. This is certainly the case with [Dima]’s tape loop echo which is actually made with a physical tape loop.

The process of building the tape loop hardware is surprisingly non-technical. By positioning a recording head and a playback head right next to one another, a delay is introduced. An echo is created by mixing the original live sound signal with this delayed signal coming from the tape By varying the speed of the tape or altering several other variables, many different-sounding effects can be achieved.

Although in practice it’s not as simple as it sounds (the device required a lot of trial-and-error), the resulting effect is one that Pink Floyd or Beck would surely be proud of. Analog isn’t the only way to go though, there are plenty of digital effects that are easily created, and some with interesting mounting options as well.

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Video FPGA with No External A/D

You have an old PC with a nonstandard RGB video out and you need to bring it to a modern PAL TV set. That’s the problem [svofski] had, so he decided to use an Altera-based DE1 board to do the conversion. Normally, you’d expect reading an RGB video signal would take an analog to digital converter, which is not typically present on an FPGA. Instead of adding an external device, [svofski] used a trick to hijack the FPGA’s LVDS receivers and use them as comparators.

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Upgrading an Old Camera with a New Light Meter

[Marc] has an old Voigtländer Vito CLR film camera. The camera originally came with an analog light meter built-in. The meter consisted of a type of solar panel hooked up to a coil and a needle. As more light reached the solar panel, the coil became energized more and more, which moved the needle farther and farther. It was a simple way of doing things, but it has a down side. The photo panels stop working over time. That’s why [Marc] decided to build a custom light meter using newer technology.

[Marc] had to work within the confines of the tiny space inside of the camera. He chose to use a LM3914 bar display driver IC as the primary component. This chip can sense an input voltage against a reference voltage and then display the result by illuminating a single LED from a row of ten LEDs.

[Marc] used a photo cell from an old calculator to detect the ambient light. This acts as a current source, but he needed a voltage source. He designed a transimpedence amplifier into his circuit to convert the current into a voltage. The circuit is powered with two 3V coil cell batteries, regulated to 5V. The 5V acts as his reference voltage for the display driver. With that in mind, [Marc] had to amplify this signal further.

It didn’t end there, though. [Marc] discovered that when sampling natural light, the system worked as intended. When he sampled light from incandescent light bulbs, he did not get the expected output. This turned out to be caused by the fact that incandescent lights flicker at a rate of 50/60 Hz. His sensor was picking this up and the sinusoidal output was causing problems in his circuit. He remedied this by adding two filtering capacitors.

The whole circuit fits on a tiny PCB that slides right into position where the original light meter used to be. It’s impressive how perfectly it fits considering everything that is happening in this circuit.

[Thanks Mojay]

Hackaday Links: March 8, 2015

Nintendo is well known for… odd… hardware integration, but this video takes it to a new level. It’s a Gamecube playing Zelda: Four Swords Adventure, a game that can use a Game Boy Advance as a controller. [fibbef] is taking it further by using the Gamecube Game Boy Advance player to play the game, and using another GBA to control the second Gamecube. There’s also a GBA TV tuner, making this entire setup a Gamecube game played across two Gamecubes, controlled with a Game Boy Advance and displayed on a GBA with a TV tuner. The mind reels.

TI just released a great resource for analog design. It’s the Analog Engineer’s Pocket Reference, free for download, if you can navigate TI’s site. There are print copies of this book – I picked one up at Electronica – and it’s a great benchtop reference.

A few months ago, a life-size elephant (baby elephants are pretty small…) was 3D printed at the Amsterdam airport. A model of the elephant was broken up into columns about two meters tall. How did they print something two meters tall? With this add-on for a Ultimaker. It flips an Ultimaker upside down, giving the printer unlimited build height. The guy behind this – [Joris van Tubergen] – is crazy creative.

And you thought TV was bad now. Here’s the pitch: take a show like Storage Wars or American Pickers – you know, the shows that have people go around, lowball collectors, and sell stuff on the Internet – and put a “Tech” spin on it. This is happening. That’s a post from a casting producer on the classic cmp message boards. Here’s the vintage computer forums reaction. To refresh your memory, this is what happens when you get ‘tech’ on Storage Wars. Other examples from Storage Wars that include vastly overpriced video terminals cannot be found on YouTube. Here’s a reminder: just because it’s listed on eBay for $1000 doesn’t mean it’ll sell on eBay for $1000.