Challenge: To build a simple tone generator that will produce a desired frequency of sound.
Parameters: The tone generator will use a provided 555 chip and 9 V battery. The circuit will be built with help from Mr. J. You will be required to produce several notes by modifying the resistance of part of the circuit.
Scoring: Your system will be scored based on the accuracy of the desired tones as measured by a tuner on a computer.
Score = (4 +T/5)(0.9)N(0.9)D
Where T is the time you take to hit the target frequencies, N is the number of the five target notes successfully recognized by the computer within the time limit of 5 minutes, and D is the difficulty of your resistance input. See below:
D = 1 Resistance input is a variable resistor, rheostat, nichrome wire, etc.
D = 2 Variable resistor is entirely home-made.
D = 3 Solutions or pastes are used. (Better living through chemistry)
D = 4 Resistance input is a photocell, light-dependent resistor, etc.
D = 5 A pressure-sensitive resistor is used.
D = 6 Resistance input is a thermistor, temperature-dependent resistor.
Whatever method you choose, your journals MUST include a detailed model that demonstrates your understanding of the physics involved.
Rank will be based on score, with lowest score earning highest rank.
Physics: The circuitry in the 555 chip is beyond our curriculum, but interesting. The basic physics of resistance, current, voltage, and capacitance should be understood for the parts of the circuit outside the chip. The production and propagation of sound waves, and the frequency (pitch), are related to kinematics, dynamics, and oscillatory motion learned in previous challenges.
Extensions: The tone generator frequency is controlled by the resistance of part of the circuit. That resistance can be changed so many ways! Your body can even be the resistor.
Help/Hints: Make sure you have a tuner app on your phone and that it matches the results my app gives, so that you are ready when the competition day arrives. If you attempt one of the more difficult projects, make sure you give yourself time to perfect your technique so that you can achieve the five notes quickly.
Quiz Topics: Simple circuitry, waves, sound.
Online Text: 13 (Waves), 14 (Sound)