Hackaday Prize Entry: DIY Guitar Multieffects

Guitar effects and other musical circuits are a great introduction to electronics. There’s a reason for this: with audio circuits you’re dealing with analog signals and not just the ones and zeros of blinking a LED. Add in the DSP aspects of audio effects, and you have several classes of an EE degree wrapped up in one project.

For his Hackaday Prize entry, [randy.day] is building a guitar multieffect. Instead of just a single distortion, fuzz, or chorus circuit, this tiny little PCB is going to have several flavors of pitch shifting, a flanger, chorus, echo, harmony, and stranger ‘digital-ish’ effects like bitcrushing.

This effects unit is built around a PIC32 and a TI audio codec which processes the audio at 64k 32-bit samples/second. This takes care of all the audio processing, but the hard work for a guitar pedal is actually the enclosure and mechanicals – it’s a hard life for stage equipment. For the foot pedal input, [randy] is using a magnetic position sensor, but there’s no word if he’ll be using a fancy die-cast enclosure or a plastic injection molded unit.

The 2015 Hackaday Prize is sponsored by:

Ghost Guitar Plays Hendrix

Purple Haze all in my brain,
lately guitars they don’t seem the same,
[Josh] is playin’ funny but I don’t know why
‘scuse me while he electrifies.

[Josh] wanted to experiment with playing a guitar by different means. We’ve seen a few guitar hacks that use servos to play, and Arduino-based guitars that replace the strings with membrane potentiometers, but he decided to try a different approach. He’s using a permanent magnet and the electromagnetic effect to play the string.

Purple Haze all around,
all those amps are runnin’ up or down.
Are my strings all goin’ left or right?
Whatever it is, electromagnetism is pushin’ me outta sight.

To do this, he put a large permanent magnet next to the string and ran an alternating current through the string itself. When the current and the magnetic field interact, the string is pushed, like the bearing of a motor.  When the current goes the other way, the string is pushed in the opposite direction. Because he is using an alternating current (driven through a MOSFET tied into a frequency generator), he was able to control the frequency of this, and find the frequencies that made the string resonate, including the harmonics that give guitars their unique sound. It’s a pretty neat hack, but don’t forget that he is dealing with quite a lot of juice: if you were to inadvertantly touch the string and ground it to earth, there is enough current in the circuit to kill you.

Yeah, [Josh’s] hack is all about the right hand rule,
I know that he’s no hacking fool,
you’ve got my E string resonating, resonating so fine
just don’t touch it, or you’ll end your time
Help me, yeah, Purple Haze!

(with apologies to the ghost of [Jimi Hendrix], guitar hacker supreme)

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Mad Max Inspired Flamethrower Ukulele

The new Mad Max movie is getting a lot of buzz, and a few people are calling it a modern classic. There’s a flamethrower guitar in the movie, which means it’s time for cosplay accouterments. Our ‘ol buddy [Caleb] loves flamethrowers and poofers, so hacking together a Doof Warrior inspired flamethrowing ukulele was natural for him.

The fuel for this uke is a can of butane actuated with a caulking gun. This setup is actually pretty clever; by removing the locking tab on the caulking gun, butane is released when the gun’s trigger is squeezed, but stops when the trigger is released. The igniter is a simple grill igniter is used to light the gas.

[Caleb] is rather famous for his flamethrowing creations. His life-size fire-breathing piranha plant uses a similar setup to shoot fire.

Video below.

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Router Fixture for Radiusing Guitar Fretboards

Unless you’ve been up close and personal with a guitar, it’s easy to miss that the fretboard (where a guitar player presses on the strings) is not flat. There is a slight curve, the amount of which varies with the type and brand of guitar. There are even guitars with fretboards that have a compound radius that changes from one end to the other.

finger board radius cutter

[Mike] is a guitar builder and needed a way to radius his own fretboards. He did what any other DIYer would, he designed and built a tool to do exactly what he needed. The fretboard radius cutting fixture consists of a new large router base that has a curved bottom. This base rests on two metal pipes and can slide both back and forth in addition to along the new base’s curve. The flat fretboard blank is secured to the fixture below the router and is slowly nibbled away at using a standard straight flute router bit. A little sanding later and [Mike] will be able to keep moving forward on his guitar builds.

Homemade 3D Carving Duplicator

[Frank] is a guitar builder and has to make a quantity of acoustic guitar bridges that wouldn’t make sense to do manually by hand each time. He wanted a way of duplicating bridges quickly and precisely but he didn’t want to go to a CNC machine. Instead, he build a 3D duplicating machine.

The machine has 3 perpendicular axes, just like a milling machine. Mounted to the Z Axis is an air powered spindle that can reach 40,000 RPM. All 3 axes are moved by the operators hands. Normally, free-hand cutting something like this would be very difficult. [Frank’s] solved this in his machine by using a stylus that is offset from the cutting bit. The stylus is the same effective length and diameter of the cutting bit and is guided over a finished bridge pattern. While the stylus is tracing the pattern, the spindle and bit are removing material from a bridge blank. The stylus is continually moved over the entire pattern bridge until the spindle is finished carving out a new bridge out of the blank.

To aid in lifting the heavy Z Axis and spindle, [Frank] added a counter balance to make tracing the pattern extremely easy. Once the new bridge is carved, it only requires minor sanding to remove the tool marks before being installed on a guitar! [Frank] admits his linear bearings and rails are very rigid but also very expensive. If you’re interested in a less-expensive 3D duplicator, check out this project.

Guitar Speaker Cabinet Actually Belongs In Garbage Can

[Dano] builds a lot of guitar pedals and amps. He needed a speaker cabinet dedicated to this task in order to be a consistent reference when checking out his electronic creations. He ordered a couple of 10″ guitar speakers…. and they sat around for a while.

Then one day at the craft store, he stumbled on an inexpensive wooden trash can. It had a tapered design and came with a lid. As would any normal person, [Dano] immediately thought these would make a perfect speaker cabinet so he bought two of them.

The trash cans would be used in an upside-down orientation. The intended lid makes for a well fitting bottom of the cabinet. Holes were cut for the speaker and two terminal blocks. Since these cabinets would be used for testing a bunch of different amps, two different terminal blocks were used to permanently have multiple connector types available.

A pair of modern kitchen cabinet handles were used as carrying handles for each of the two cabinets. If a speaker cabinet one speaker tall is cool, a cabinet two speakers tall must be twice as cool. To get there, the two cabinets were bolted together using electrical conduit as an industrial looking spacer. Those brackets bolted to the sides of the bottom cabinet are actually Ikea shelf brackets that [Dano] had bought and never used. The Ikea brackets support casters making for easy moving around the studio.

Overall, [Dano] is happy with how his cabinets sound. They are very unique and interesting at the least. We’d be happy to play some riffs through them!

Wireless Mic Helps Guitarist Rock Out Un-Tethered

Any guitarist knows what a tangled mess of cords can come out of a long jam session. One possible solution would be to get a wireless guitar system, however, such a setup can range in price from about 50 to several hundred dollars. That’s a big price to pay for not having to untangle some guitar cords.

[mattthegamer463] wanted a wireless setup but didn’t want to spend the cash on one. He’s a tinkerer and had a spare wireless microphone setup hanging around. So, he decided to try converting the wireless mic to work with his guitar.

Both microphones and guitar pickups work in similar manner. In a guitar pickup, the vibrating guitar string disturbs a magnetic field and induces a current in the pickup’s coil. That current is the guitar’s signal. Microphones are similar, air pressure waves vibrate a diaphragm or ribbon which then disturbs a magnetic field to create the signal. [mattthegamer463]  thought these principles were close enough for him to make quick work of the conversion.

First, the microphone was taken apart and the diaphragm module was removed, cutting the two wires that ran into the mic’s handle. A hole was then drilled into the wind screen so a 1/4″ jack could be installed. [mattthegamer463] states that it’s important to electrically isolate the jack from the wind screen or the signal and ground wires will short and the project won’t work. The two wires that were previously connected to the diaphragm module are then soldered to the newly added jack and the mic was screwed back together.

To use it, a patch cord is run from the guitar into the jack on the mic. The stock wireless receiver from the mic system is then plugged into the guitar amp. The modified ‘mic’ now transmits the guitar signals to the guitar amp! You may think it would be awkward to hold that mic while jamming. You’d be right if [mattthegamer463] didn’t come up with a nice looking aluminum and rubber belt clip.