Results

General Operation

We built a fully-functioning bass guitar tuner. It is able to read the frequency of a note from the bass guitar and then tune each of the strings of a standard 4-string bass guitar (E, A, D, and G). Frequency and note accuracy are continually displayed on an LCD screen.

The tuner consists of the following three main components (photo diagram):

• Fixture - holds the motor and attaches it to a tuning peg
• Frequency measurement circuit - hardware that reads the signal from the guitar and converts it into a time period of the played note
• Handy Board Box - microcontroller reads the measurement from the circuitry and tells the motor what to do

Flowchart of how the system works - shows how the different parts of the tuner interact to tune the guitar

Performance

The tuner is set in software to tune a string to within 0.5 % of the actual note's frequency. In practice the tuner was accurate within several percent. At its best the tuner consistently tuned the string to less than 1 Hz of the actual note (referenced to a comercially available tuner). Successful tuning takes approximately 3-7 seconds.

Sources of variation in results include:

• ambient noise (the testing guitar used a microphone pickup)
• use-to-use variation in RC circuitry timing
• the amount out of tune the string originally was
• aberrant readings from the inital string pluck

Goals

We met our goal of building a device that is able to tune a guitar. The final result is more complex than we had initially envisioned in terms of number of components. This complexity grew from the need for a clean and fairly stable frequency reading. The specifications of our tuner had to be reduced though. We initally wanted the tuner to be able to perform non-standard tuning, but eliminated that in order to simplify the project. We also had to limit our tuner to a 4-string bass guitar. The motor fixture provides the flexibility to tune on any peg configuration, but it is somewhat cumbersome.

Multimedia

Documentation