This webpage details the main components of the SMARTune system and how they connect to each other. The main components are the user interface, pickups, the microcontroller, the tuning mechanism, and the power supply. The figure on the right indicates the general connections between the physically separate systems through color coding.
In the SMARTune system, the user will interact with the system in three basic ways: 1. through the user interface, which will consist of a screen and some buttons, 2. by strumming or plucking the strings of the bass guitar, or 3. by manually tuning the bass guitar using the tuning keys in the tuning mechanism.
Post-Project Update: See the team's Final Report for up-to-date information regarding the final prototype's system layout.
Post-Project Update: The team implemented the user interface portion of the system with a 16 x 2 character LCD screen (shown right). Mechanical pushbuttons allow navigation. The user interface takes user input, and send it to the microcontroller for processing. It will also receive power from the power supply.
The team implemented the user interface within the microcontroller. The user uses the left, right, up, and down pushbuttons to select which notes to tune to, and then navigates to "GO!" and presses the enter button. This initiates the tuning sequence.
Instead of standard pickups, the the team decided to use polyphonic pickups. A polyphonic pickup contains small copper windings around individual magnetic cores. In a polyphonic pickup, there are two output wires from each of these magnet-coil pairs. The team using quadraphonic pickups for this project; this is a subset of polyphonic pickups consisting of four distinct pickups. The four magnet-coil pairs of the quadraphonic pickup will send induced signals from the strings of the bass guitar to the microcontroller through these output wires. In the figure on the right, the polyphonic pickups are on the bottom left, and the standard pickups are top right. Standard and polyphonic pickups are discussed further on the design page.
The team is in the midst of selecting a microcontroller. This is detailed on the design page. The analog to digital converter portion of the microcontroller will take in signals from the pickups and pass them to the microprocessor. The microprocessor will take in these signals and the user control signals, process each of them, and output motor control signals to the tuning mechanism. This is shown on the right.
This component will take in an input from the user interface and the pickups, and process them using the power from the power supply. The microcontroller is displayed in Figure 9. The microcontroller takes in the user input signals first to determine what actions it should take. If the user specifies a specific tuning, and to begin tuning, then the microprocessor sends a signal to the ADC to begin sampling. The ADC converts the analog signals to digital signals and sends them to the microprocessor; which processes them first with an FFT algorithm. This algorithm determines the most prevalent frequency within the four input waveforms, one at a time, and outputs the results to a function that assigns a note to those frequencies. The microprocessor then compares those assigned frequencies to the frequencies associated with the notes of the scale specified by the user through the user control signals. The difference between the user input scale and the sampled scale determines the type of motor command, positive rotation or negative rotation, that is sent out of the microcontroller through the PWM outputs. PWM, or Pulse-Width Modulation, is discussed on the concepts page.
The electrical portion of the tuning mechanism involves three main signals, shown right: the motor’s power, the pulse-width modulated (PWM) signal, and the mechanical output (which is detailed in the next paragraph). The motor's power is a 6V input from the power supply. A PWM signal is used to control the mechanical rotation of the motor. The output of the motor is used to physically turn the gears within the servo’s structure.
Mechanically, the motor is driven by an electrical signal. The diagram is depicted on the right. This motor turns a gear reduction system that connects to an output shaft. The output shaft will be attached to a worm. This worm turns a worm gear, which changes the tension in the string. The user is also able to utilize the manual tuning key in order to manually tune the bass guitar.
The power supply will consist of a 1500 mAh battery (discussed in Section 7.1.4). It will be rechargeable by a 120V wall adapter. The battery will supply power to the user interface, microcontroller, and motor through a voltage regulator.
The first alternative that The Tune Squad considered was to tune at the bridge of the guitar. Tuning at the bridge brings all of the tuning hardware to the body (or even inside) of the guitar, where it could be mounted and hidden. According to team member Cheyn Rushing, this approach would add complexity to the entire system that is not desirable; it requires either designing to provide compatibility with current string implementations, or designing a new string for the tuning system. It also would require high-torque motors to hold the strings at a constant tension.
A second alternative was a digital auto-tuning system. This system would have digitally altered the signals generated by each string, instead of tuning them. This system is seen as “cheating” in the team’s eyes, and is rejected for that reason.
The third alternative that The Tune Squad considered was tension-based tuning. This method is rejected for digital signal processing through polyphonic pickups, as it is easier to integrate into a guitar. Tuning based on tension readings would require six sensors, or one larger sensor, with power and data wires running to the microcontroller for each. Tuning using polyphonic pickups only required one set of polyphonic pickups and twelve small wires, two for each pickup coil.
The final alternative tuning style was found in a self-tuning piano designed by Don Gilmore that passes a certain amount of current through strings in a piano to change the string tension.1 A higher current means thermal energy is transferred to the strings, causing the metal to expand and the pitch to decrease. Lower current through the piano allows the string to cool and increase in pitch. It is an interesting system that could be implemented in a guitar. However, it appears that the system would have to be constantly running in order to keep the tension at the desired level. This is undesirable because the team strives to care for the environment through power consumption reduction.
- 1 From the article on Gizmag.