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Self-tuning 'robot' guitar ready for spotlight

Posted: 21 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:self-tuning guitar? robot guitar? control signal?

Gibson Guitar Corp. has a special treat this holiday season as it demos the first self-tuning guitar on Dec. 7. The initial price for the limited-edition blue-silverburst Les Paul Robot Guitar will be $2,500, with a standard edition self-tuning "robot" slated to go on sale in January 2008.

"We're trying to make a better guitar, but innovation is initially frowned on by most guitarists," said Gibson CEO Henry Juszkiewicz. "So we've chosen a non-invasive technology from our partner!Tronical!that you can completely remove. Musicians value the tradition of an instrument just the way it is, so if you unbolt our electronics you have a normal Les Paul guitar with no extra holes in it or anything."

Earlier this year, Gibson announced that it had acquired an exclusive worldwide license to market and distribute the Powertune system from Tronical GmbH, a retrofit kit that enables any guitar to be converted to a self-tuning guitar for about $900. Other such kits are available from companies such as TransPerformance Corp., but the instruments have to be permanently altered. In contrast, Tronical's Powertune installs with no alternations to the original instrument, according to Gibson.

Next year Gibson will roll out several new guitars with a customized version of the Powertune system, with the current Dec. 7 debut just marking the initial limited edition model. The company will also be launching a new line of Ethernet guitars, which have more features and a lower price than its current model, the $4000 HD.6X Pro digital Les Paul, next year.

Easy learning
Tuning the guitar is the first lesson taught to newbies, but the task is deceptively simple. If done manually!by tuning each string to match an adjacent one!slight mistakes on string one multiply as the guitarist moves on to strings two through six. The solution is to use either a manual algorithm!to cross-check octaves among non-adjacent strings!or to use a separate electronic tuner.

Unfortunately, the manual algorithm requires a trained ear!which new musicians have yet to develop!and a separate tuner, which turns the guitarist into a robot by issuing directions on which way to turn the tuning pegs. Now Gibson has put the robotics into the guitar, with motorized tuning pegs and smart control circuitry that not only keeps your guitar perfectly tuned, but can automatically change tunings to six popular alternatives to standard tuning.

To tune Gibson's Robot Guitar, the player merely pulls out the volume knob until it clicks, then strums the guitar without touching the neck!the string's tuning pegs will all turn simultaneously until every string is perfectly tuned. For different tunings, a twirl of the knob shows the setting for Open-E, Open-G, Drop-D, Double-Drop-D, A and E-flat tunings on LEDs in the top of the knob.

Besides just tuning, Gibson's Robot Guitar can also fine-tune its 12th-fret octaves so the guitar has perfect intonation in all playing positions (a task today relegated to guitar service technicians with specialized stroboscopic tuners).

Mechanical strings
Electronic engineers might think that building a self-tuning guitar is not an especially daunting task, but the architecture for achieving that goal without changing the construction and appearance of the guitar involved several interesting innovations unique to the Gibson Robot Guitar. For instance, the strings themselves serve as conduits for both power supply and control signals among the five electro-mechanical subsystems built by Gibson into the Robot Guitar.

The mechanical tuning itself is accomplished by special motorized heads that embed light-weight servo-motors into the tuning pegs for each string. Mounted into the head-stock of the guitar!between the two rows of three tuning pegs on each side!is an encapsulated printed-circuit board with a microprocessor that controls the motors.

The frequency of each string is sensed in the bridge, which holds the strings away from the body at the bottom of the guitar. Each string has a separate adjustable bridge segment, under which is a piezoelectric sensor that senses and transmits the strings signal to a microcontroller in the guitar's body. Algorithms there determine the frequency of each string, compare it to what it is supposed to be!according to the setting on the LED indicator!then send a control signal along each string from the tailpiece to the neck microprocessor, which controls the motors turning the strings.

- R. Colin Johnson
EE Times

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