EMG Tutorial Lets You Listen to Your Muscles

What with wearable tech, haptic feedback, implantable devices, and prosthetic limbs, the boundary between man and machine is getting harder and harder to discern. If you’re going to hack in this space, you’re going to need to know a little about electromyography, or the technique of sensing the electrical signals which make muscles fire. This handy tutorial on using an Arduino to capture EMG signals might be just the thing.

In an article written mainly as a tutorial to other physiatrists, [Dr. George Marzloff] covers some ground that will seem very basic to the seasoned hacker, but there are still valuable tidbits there. His tutorial build centers around a MyoWare Muscle Sensor and an Arduino Uno. The muscle sensor has snap connectors for three foam electrodes of the type used for electrocardiography, and outputs a rectified and integrated waveform that represents the envelope of the electrical signal traveling to a muscle. [Dr. Marzloff]’s simple sketch just reads the analog output of the sensor and lights an LED if it detects a muscle contraction, but the sky’s the limit once you have the basic EMG interface. Prosthetic limbs, wearable devices, diagnostic tools, virtual reality — the possibilities are endless.

We’ve seen a few EMG interfaces before, mainly of the homebrew type like this audio recorder recruited for EMG measurements. And be sure to check out [Bil Herd]’s in-depth discussion of digging EMG signals out of the noise.

MIDI Guitar Pedals

Ever since Jimi Hendrix brought guitar distortion to the forefront of rock and roll, pedals to control the distortion have been a standard piece of equipment for almost every guitarist. Now, there are individual analog pedals for each effect or even digital pedals that have banks of effects programmed in. Distortion is just one of many effects, and if you’ve built your own set of pedals for each of these, you might end up with something like [Brian]: a modular guitar pedal rack.

ae0fmjxTaking inspiration from modular synthesizers, [Brian] built a rack out of wood to house the pedal modules. The rack uses 16U rack rails as a standard, with 3U Eurorack brackets. It looks like there’s space for 16 custom-built effects pedals to fit into the rack, and [Brian] can switch them out at will with a foot switch. Everything is tied together with MIDI and is programmed in Helix. The end result looks very polished, and helped [Brian] eliminate his rat’s nest of cables that was lying around before he built his effects rack.

MIDI is an extremely useful protocol for musicians and, despite being around since the ’80s, doesn’t show any signs of slowing down. If you want to get into it yourself, there are all kinds of ways that you can explore the studio space, even if you play an instrument that doesn’t typically use MIDI.

Scrap Bin Mods Move Science Forward

A first-time visitor to any bio or chem lab will have many wonders to behold, but few as captivating as the magnetic stirrer. A motor turns a magnet which in turn spins a Teflon-coated stir bar inside the beaker that sits on top. It’s brilliantly simple and so incredibly useful that it leaves one wondering why they’re not included as standard equipment in every kitchen range.

But as ubiquitous as magnetic stirrers are in the lab, they generally come in largish packages. [BantamBasher135] needed a much smaller stir plate to fit inside a spectrophotometer. With zero budget, he retrofitted the instrument with an e-waste, Arduino-controlled magnetic stirrer.

The footprint available for the modification was exceedingly small — a 1 cm square cuvette with a flea-sized micro stir bar. His first stab at the micro-stirrer used a tiny 5-volt laptop fan with the blades cut off and a magnet glued to the hub, but that proved problematic. Later improvements included beefing up the voltage feeding the fan and coming up with a non-standard PWM scheme to turn the motor slow enough to prevent decoupling the stir bar from the magnets.

[BantamBasher135] admits that it’s an ugly solution, but one does what one can to get the science done. While this is a bit specialized, we’ve featured plenty of DIY lab instruments here before. You can make your own peristaltic pump or even a spectrophotometer — with or without the stirrer.

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3D Printed Moon Phase Clock

Someone once observed that the moon is a harsh mistress. But that doesn’t mean you can’t keep track of her, specially with this awesome moon phase clock that [G4lile0] designed and built.

It uses a 3D printed moon model combined with a series of LEDs to create the phases. These LEDs are driven by an Arduino that calculates the phase to show, as well as driving a small OLED display that shows the date and time. There is even a party mode for all of those lunar raves that you host.

[G4lile0] has done an excellent job of documenting the code that drives the lamp, so it would be easy to add features, or adapt this design to show the phases of another moon or add other features. It’s an excellent overall design, and kudos to [G4lile0] for doing it all with open source tools like FreeCAD.

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Only One Button? No Problem!

Sometimes less is more. This is especially true when dealing with microcontrollers with limited I/O pins. Even if you have lots of I/O, sometimes you are need to pack a lot into a little space. [Hugatry] was inspired by the simple interface found on a lot of flashlights: one button. Push it and it turns on. Push it again, and it switches modes. You cycle through the modes until you finally turn it back off. One button provides mutliple functions. The question is how can you use a power switch as an I/O device? After all, when you turn the power off, the microprocessor stops operating, right?

[Hugatry’s] answer is quite simple. He connects a resistor/capacitor network to an I/O pin (or multiple pins). When the processor turns on initially, the pin will read low and the capacitor will charge up. If you turn the power off, the CPU voltage will fall rapidly to zero, but the voltage on the capacitor will discharge slower. If you wait long enough and turn the power on, there’s no difference from that first power on event. But if you turn the power on quickly, the capacitor voltage will still be high enough to read as a logic one.

What that means is that the processor as part of its start up can detect that it was recently turned off and take some action. If it remembers the previous state in nonvolatile memory, you can have the code cycle through multiple states, just like a flashlight. You can see a video of the setup, below.

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A Laser Effect Projector Built with Safety in Mind

There’s just something about wielding a laser pointer on a dark, foggy night. Watching the beam cut through the mist is fun – makes you feel a little Jedi-esque. If you can’t get enough of lasers and mist, you might want to check out this DIY “laser sky” effect projector.

The laser sky effect will probably remind you of other sci-fi movies – think of the “egg scene” from Alien. The effect is achieved by sweeping a laser beam in a plane through swirling smoke or mist. The laser highlights a cross section of the otherwise hidden air currents and makes for some trippy displays. The working principle of [Chris Guichet]’s projector is simplicity itself – an octagonal mirror spun by an old brushless fan motor and a laser pointer. But after a quick proof of concept build, he added the extras that took this from prototype to product. The little laser pointer was replaced with a 200mW laser module, the hexagonal mirror mount and case were 3D printed, and the mirrors were painstakingly aligned so the laser sweeps out a plane. An Arduino was added to control the motor and provide safety interlocks to make sure the laser fires only when the mirror is up to speed. The effect of the deep ruby red laser cutting through smoke is mesmerizing.

If laser sky is a little too one-dimensional for you, expand into two dimensions with this vector laser projector, and if monochrome isn’t your thing try an RGB vector projector.

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Power Wheels Rescued, Restored and Enhanced

It seems power wheels are like LEGO — they’re handed down from generation to generation.  [Nicolas] received his brand-new Peg-Perego Montana power wheels in 1997 as a Christmas present. After sitting in a barn for a decade, and even being involved in a flood, it was time to give it to his godchildren, though not without some restoration and added features. His webpages have a very good write-up, just shy of including schematics, but you’ll find an abbreviated version below.

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