Electronic Keyboard

A speaker converts electrical energy into sound. It does this by using the energy of an AC electrical signal to create mechanical vibrations. These vibrations create vibrations in air pressure or sound waves. Speakers need a high current and a low voltage to operate correctly. This is the reason why a transformer is used before electricity can make it to the speaker. The battery has high voltage and low current; the transformer reverses that. The transformer is composed of two coils, or inductors. These coils have different magnetic properties which affect the electrons flowing between them.

This schematic is of the basic oscillator circuit essential to the functioning of the keyboard. It uses feedback which adjusts the input based on what the output is doing. The frequency is controlled by this feedback and will increase with drops in resistance or capacitance. It will also increase with lower inductance, but the inductance cannot be changed on the keyboard.

On the diagram, there are two long wires denoted by dotted lines. These wires can be connected to resistors to create different sounds. In order for the keyboard to make different notes there needed to be different buttons. The resistance for each key on the keyboard has been specifically tuned to give a note. This has been done with use of potentiometers which are resistors with variable resistances controlled by knobs. The two long wires were split into five wires each. One of the split wires went to every button and the other wire went to every potentiometer. The potentiometers had another wire each connected to a button. When each button is pressed, a different note is produced based on the resistance of each potentiometer. The notes of the keyboard are as follows:

Ab( 831 Hz), Bb( 932 Hz), C( 1047 Hz), D( 1175 Hz), Eb( 1245 Hz)

The oscillation frequency can be found using the equation where L is the inductance and C is the capacitance. The inductance for each note can be found by rearranging the equation into: L = 1/(4ПЂ2CF2). With this equation, the induction of each note can be determined:

Ab = 0.78 henrys Bb = 0.62 henrys C = 0.49 henrys D = 0.39 henrys Eb = 0.35 henrys