Monday, February 13, 2012

Magnetic Table CV Controller

Here is one of my designs that I based off of a magnetic pendulum toy.  The toy consisted of a dangling string with a magnet on the end of it; then it hovered over magnets on a table that either repelled or attracted the string magnet; the stringed magnet then maneuvers around in crazy patterns due to the position of the table magnets.

There are 2 control voltage outputs for this device; one for the X axis, and one for the Y.  They vary from 0 to 5 volts.  These can be used to change any parameter in a synthesizer or effects system to make interesting sounds.  For instance, the X axis could control the pitch of an oscillator, while the Y axis could control the volume.  Another example could be the X axis controls a delay time, while the Y axis controls the feedback of the delay unit.  A third example (and a little more abstract) is to have the X axis control the length of a sequence pattern, and the Y axis control the tempo of the sequence.

One interesting thing about using the magnetic table to control sound is that when the pendulum passes over a magnet with a pole that attracts the pendulum, it overshoots a bit, then swing back toward the magnet and overshoots again, continuing to oscillate in a damped, simple harmonic motion.  If the magnet is stronger (you can use larger magnets or stack them to make them have a stronger attraction or repulsion), then this oscillation is faster.

For my design, I mounted an upside-down potentiometer-joystick on an arm above a plate of steel, then machined a long, aluminum rod to replace the shaft that was inside the joystick. At the end of this rod, a cavity was made and a powerful magnet was epoxied into the cavity.  This magnet can freely hover over the steel plate.  If  magnets are placed on the table / plate, then they can repel or attract the rod (and therefore move the joystick) based on their position and polarity.  The potentiometers on this joystick are wired as voltage dividers/ attenuators for DC voltage.  There is a 9-volt battery inside going to a linear 5-volt regulator, then to the divider.  The knobs on the front of the box control offset and range for X and Y.


  1. This looks very interesting - please make a video documentation of it in action!

  2. The toy consisted of a dangling string with a magnet on the end of it; then ...