Poor Man's Theremin

Here's how you can play music with your wireless network card.

If you're interested in gaining some experience playing the theremin but don't want to spend a lot of money or build the kit, try the “Poor Man's Theremin” (PMT), written by Seth David Schoen.

The PMT turns a laptop computer with an 802.11b card into a theremin-like instrument, using the signal strength reported by the card to control the pitch of a note. To try it, first compile this C program, called ttone, using the command cc -o ttone -lm ttone.c.

Listing 1: ttone.c
#include <math.h>
#include <linux/kd.h>
const int A = 440;
const float r = 1.05946;
int pitch(int base, int observed){
    return (int) A * pow(r, (observed-base));
    }
int main(int argc, char *argv[]){
    int base, observed;
    if (strcmp("off", argv[1])){
        base = atoi(argv[1]);
        observed = atoi(argv[2]);
        ioctl(0, KIOCSOUND, 1190000 / pitch(base, observed) );
    } else {
        ioctl(0, KIOCSOUND, 0);
    };
}

Put the ttone executable in a directory that's in your PATH.

Now run the following shell script, called pmt.sh, and move into range of an 802.11b access point. You can change the pitch by moving closer to or further away from the access point or by moving your hand over the 802.11b antenna in a theremin-player-like manner.

Listing 2: pmt.sh
#!/bin/sh
# Poor Man's Theremin
m=100
oldQ=foo
[ $1 ] && m=$1
while :
do
Q=$(iwconfig 2</dev/null | grep Link.Quality | cut -d: -f2 | cut -d/ -f1)
if [ $oldQ != $Q ]
then
    ./ttone $m $Q
    fi
    oldQ=$Q
    done

The Poor Man's Theremin does not have the volume control of a proper theremin, and the pitch changes in discrete steps instead of continuously. Implementing these features is left as an exercise for the reader.

Don Marti is editor in chief of Linux Journal.

______________________

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix