Medita - a Sonic Drone Meditation Device

This device makes use of electro-magnets to actuate ferrous materials, such as a steel string or plate. This allows for an instrument to be played without coming in physical contact with it. This is similar to an e-bow, but with a much more focused range allowing for a more intense actuation of specific frequencies. Using this technique, we can explore the harmonic content of any ferrous material and use it to influence our relaxation practices.

To do this, we will use materials from an electric bass, which are essentially:

Wood (approx. 32’’ length)
String (I used a standard D’addario D-string)
Mono-string bridge
String Tuner
Electro-magnet 40mm (Amazon)
Arduino Uno ()
N-Channel Mosfet
Power supply 12v

All these materials are available on Amazon.com (maybe not the wood)

Step 1: Materials

First off, let's get some supplies:

Bass strings
I tend to gravitate towards lower frequencies so I chose to use electric bass strings, but you can use guitar strings if you prefer. Guitar strings would provide higher pitched and "brighter" tones, while bass string allow for lower pitched "warmer" and "rounder" tones.
String tuning peg + Monorail Bridge
We need a mechanism to tension the string. Since we are only using one string, let's use a monorail bridge system and a single string tuning peg.
Electro-magnet
To actuate the string, we'll be using and electro-magnet. An electro-magnet is a coil of wire (usually copper) that generates a magnetic field when provided with electricity. If we provide electricity to the magnet at a frequency rate equal to those found in the harmonic spectrum of the tensioned steel string, then we can cause it to resonate at that frequency (and many frequencies within it!). We also need this magnet to be powerful enough to manipulate the string so let's go ahead and use a 12v 40mm.
Hardwood (I used Walnut)
Like many acoustic instruments we need some sort of resonant chamber so the sound can be amplified and characterized. Hardwoods are good because they are dense enough to carry the frequencies throughout and add character to the final sound. Walnut is generally thought to produce a warm tone with good mid-range.
Arduino Uno
We will be using the arduino's Tone library to generate squarewave frequencies that switch on/off very rapidly to pulse the electro-magnet with electricity.
N-channel Mosfet
The mosfet will act as a gate between the power supply and the electro-magnet, it is controlled by the Arduino

Step 2: Arduino + N-Channel Mosfet Circuit

Let's hook up the mosfet to the Arduino. We will use the signal pin on the arduino to control the flow of electricity between the power supply and the electromagnet.

Here is the Arduino code:

/*

Medita - A Sound Drone Meditation Device

Sends a frequency to an electromagnet which actuates a steel string, causing it to resonate pleasantly.

2016 Epic Jefferson

*/

const int magnet = 3; // the pin that the magnet is attached to

byte note = 80; // This is the frequency we want to push the string with

void setup() {

pinMode(magnet, OUTPUT);

}

void loop() {

tone(magnet, note);

}

Step 3: To the Woodshop!

Make a box! Stretch a string over the surface using the bridge and string tuning peg. For the frequency we're using the distance between these should be approximately 32". Place the electromagnet in between them, about 7" from the bridge.

Step 4: Assemble

Once you put all the parts together. Sand it down to size and glue it together. Place all the electronics inside and stretch out the string between the bridge and the tuning peg. Make sure to not over tension just yet. In the next step we'll be looking for the correct frequency using the electro-magnet.

Step 5: Tune It!

Once all the electronics are in the box. Turn it on and start tensioning the string until it starts resonating on it's own. Be sure to go slowly andnot over tension the string to the point of breakage. If you feel it's too tight, it probably is. Un tension the string until you can't hear a note and the string has enough slack and start tensioning again. Once you've found the right frequency it'll be very obvious and you're string will start vibrating due to it's fundamental frequency matching that of the magnet. Remember that string take some time to stretch out properly so you may have to tune it several times before it will stay in tune.

Step 6: Meditate

You now have a Sonic Drone Meditation Device. As an exercise, sit down in front of it and listen for changes in the actuation and characteristics of the sound. This is due to phase difference between the frequency of the string and the electro-magnet.

You can also experiment filtering the sound by manipulating a the box lid. Play around with this and create an engaging sonic experience with your device!