No matter the size of the stage, most gigging guitar players are likely to have to return to the same spot from time to time to change the tone, increase the volume, check tuning or to operate the wah effect. Thanks to a team of students from Purdue University's School of Mechanical Engineering, the last of those has now been liberated from the pedal board and strapped to the player's ankle. This doesn't involve attaching a large brick-shaped wah pedal to one leg, as one's imagination might suggest, but wearing a small wireless transmitter and a couple of sensors instead. Players operate the Ghost Pedal in much the same fashion as a physical pedal, the sensors registering the rocking motion of the foot and feeding data to a base station connected to the amplifier.

The ankle unit is made up of a variable resistor sensor that tracks the movement of the ankle and a sustain sensor which either accepts the virtual wah feed or ignores/sustains it. When the unit is first switched on, there's a ten second calibration period where a wearer's ability to flex the ankle is determined and stored. After that the device goes into free-play mode which allows the user to virtually control the amount of wah by changing the angle of the foot from the floor, in much the same motion used with an actual wah pedal.

If the player wants to bypass the wah effect to move position, the sustain sensor is positioned at the inner ankle and is tapped with the other foot to activate. When the guitarist has climbed atop the Marshall stack or simply moved to another part of the stage, another tap will bring back the wah. The signals from the ankle unit are sent wirelessly to a micro-controller that translates them into instructions for the wah circuit's resistors. The analog nature of the signal is maintained by using a digital potentiometer to marry the digital and analog circuitry.

Although virtual pedal control is currently limited to the wah effect, the team says that there's no reason why such a device can't be adapted to wirelessly control other effects - such as pitch, volume, distortion and so on. The calibration mode also means that one unit can be easily used by different players - a very useful feature.

The team includes Garrett Baker, Will Black (pictured above), Matthew Boyle, Brett Hartnagel, Christine Labelle, Adam Pflugshaupt, Nick Sannella and Robbie Hoye, who all graduated from Purdue last year and created the patent-pending Ghost Pedal as a senior project. Licensing of the Ghost Pedal technology is currently in the hands of Purdue's Office of Technology Commercialization.

Source: Purdue University Office of Technology Commercialization

All images courtesy of the Purdue Research Foundation