Our product:

A mechanical trumpet tuner that takes an input played note and adjusts the tuning slide accordingly for the trumpet to be in tune and stops when the goal note is met.

Functional Requirements for the Trumpet Tuner:

Accurately tunes to within +/- 0.75Hz (3 cents)
React to signal within 1 second
Removable without affecting tune
Power on/off
Mass < 0.5 kg

Work in Progress

Not our final design, but a working model showcasing:

The tone being flat (blue LED)
The tone being sharp (red LED)
and the tone being in tune (green LED)

Final Working Product

The design is shown here reacting to a purposefully sharp signal, a purposefully flat signal, and then shown tuning the open tuning note of the trumpet.

Assembly Schematic

The assembly drawing on the left shows how the PCB and the motor fit into the housing component with two switches inserted at the top of the housing. The battery pack is shown at the bottom of the housing, with all four batteries fitting within the white slide shown next to the batteries. The tuning slide attachment is shown with the power screw and thumb screw. The housing for the electret microphone is also shown here, along with its attachment clip. All of these parts come together to form our automatic trumpet tuner.

How it works

The device works by reading an input signal from an electret microphone that is clipped to the bell of the instrument. The signal from the microphone is run through a Fourier transformation, and the peak frequencies are compared against the set target frequency of the tuning note. The Arduino midi note library is used to determine how flat or sharp the incoming signal is relative to the target note. If the input is sharp, the motor turns counterclockwise to push the slide out. If the input is flat, the motor turns clockwise to pull the slide back in. When the input is in tune, the motor stops moving.

The image on the left shows the input reading from the microphone as well as the calculated sharp or flat value.