PORTLAND, Ore. A second-generation self-tuning Robot Guitar was recently announced by Gibson Guitar Corp. (Nashville, Tenn.). Two new models are available--a Les Paul Studio Ltd. and an SG Special Ltd.--both offering a new locking input jack. The first-generation Robot Guitar was superseded by the new second-generation models earlier this month. The new instruments, which sport a metallic purple finish, are now sold out, but EE Times has learned that a new metallic green finish will be announced by Gibson soon.
All second-generation Gibson Robot Guitars have an automatic-locking input jack from Neutrik AG (Liechtenstein, Germany). The locking phone jack prevents accidental disconnection by latching whenever a standard 1/4-inch plug is inserted. Automatically mated plugs unlock only by pressing red release tab.
New for the second-generation Robot Guitars is the inclusion of an SG model, which was introduced in 1961 as a new lighter weight body style, dubbed the "solid guitar"--SG. The SG Special Ltd. has a more slender neck compared with the classic round-neck of the original Les Paul, which was designed in the 1950s, and which is still used today for the second-generation Robot Les Paul Studio Ltd.
Both the Robot Les Paul Studio and Robot SG Special models share the same automatic tuning functions designed by Tronical GmbH (Hamburg, Germany). Tronical's patented Powertune system uses motorized tuning pegs that all turn simultaneously until every string is tuned. For alternative tunings, a twirl of a knob shows illuminated settings for six non-standard tunings (Open-E, Open-G, Drop-D, Double-Drop-D, A and E-flat); custom tunings can be substituted by the player. All of Gibson's Robot Guitars can also adjust the intonation of 12th-fret octaves (a task usually relegated to guitar service technicians with specialized stroboscopic tuners).
Inside tuning up
As revealed by a Portelligent (Austin, Texas), tear-down of the original Robot Guitar, two Silicon Labs C8051F120 mixed signal microcontrollers--one in the body and one in the headstock--control all the automatic tuning functions. The Silicon Labs C8051F120 uses an 8051 core with a 16-bit multiplier/accumulator, a built-in 12-bit analog-to-digital converter, two built-in 12-bit digital-to-analog converters, 8 kbytes of data RAM, 128 kbytes of flash program memory, and 64 bits of digital input/output (I/O).
Sensing the frequency of the strings are six individual piezoelectric transducers, one under each string in the bridge. These individual measurements are multiplexed down to a single line feeding the microcontroller in the body. To connect the microcontroller in the body to the second microcontroller in the headstock, the Gibson Robot Guitars use the strings as wires instead of embedding a cable into the neck, thereby preserving the stock profile of the guitars.
Even though the guitar strings provide six connection lines between body and headstock electronics, they are not used for sending the frequency information about each string separately, according to Portelligent. Instead, two strings are used for power and two for ground, leaving the remaining two for the multiplexed instructions. That redundancy enables the Robot Guitars to continue functioning normally even if a string breaks.
The information on which way to turn each peg during tuning is delivered over a Controller Area Network (CAN) bus employing an NXP AU5790 controller located in the body. The CAN controller delivers packet data with tuning instructions for all the pegs to the microcontroller in the headstock, which decodes which signals are intended for each tuning peg motor, and sends those control signals to three Rohm BA6845FS dual channel motor drivers that control the tuning-peg motors for each of the six strings.
A 2.4 volt NiCd battery pack in the body makes use of Linear Technology DC-to-DC converters to step up the power supply voltage enough to drive the tuning peg motors. Tuning heads have a tiny circuit board behind each tuning-peg motor that picks off the signals intended for that particular string, including power and ground.
For a detailed look at these second-generation guitars, see this "Slide Show."
To experience how these guitars work, listen to this Podcast."