IFD:Printing Acoustic Interfaces: Difference between revisions

When we change the distance between the coils in our paper built air core transformer, the actual amplitude (volume) of the high frequency tone increases or decreases. To get the actual volume information of this high frequency tone, we use the half wave rectifier. The circuit consists of a diode, a resistor and a capacitor. The diode lets only the positive current travel through it (in the direction implied by the arrow) and blocks the negative current, running against its direction. This leaves us with the positive half of the sending waveform. The final thing we need to do is average this positive half wave to get the average amplitude of this half wave. This averaging is achieved by the capacitor and the resistor. When the capacitor is charged, and there is no voltage on the right side of the diode, a discharge current will flow through the resistor to ground. The amount of discharge current is controlled by the resistor. The bigger the resistance the less discharge current will flow. We need to adapt  the value of this resistor to have the capacitor discharge just a little bit, before the next positive half wave arrives at the right side of the diode. Then, if we receive less current in the second coil, the average charge on the capacitor decreases, following the actual acoustic waveform between our two sheets of paper.

==Further Reading==