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Xuemin Hang: xh24@cornell.edu Marcel Xu: mx23@cornell.edu
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Speed The synthesizer (MCU1) outputs an audio signal immediately when a note is played. There is no detectable time delay between the keyboard press and the sound generation. Similarly, the video generator (MCU2) displays the corresponding note on the television screen with no visible delay. The operation of both the PC interface and the music keyboard interface are fully concurrent, i.e., the keyboard operates normally even when the instrument to be played is being selected at the PC interface. Initially, we had the occasional problem of video artifacts appearing when we played too many notes at once. This is due to the once-per-frame calculations spilling over to the next frame. Therefore, we reduced our code to limit the TV display to show chords of up to 2 notes only, so that artifacts would no longer appear.
Accuracy The synthesized music frequencies were measured using the oscilloscope and compared with the theoretical music frequencies. The theoretical frequency resolution, for the 24-bit accumulator and 40-cycle loop, is (16 MHz/40)/(2^24) = 0.02 Hz. We should thus be able to achieve frequencies within 0.02 Hz of the ideal. The measured frequencies and their theoretical values are shown in the following table:
Clearly, in the above table, the discrepancy between the actual and desired frequency varies between 0.2 Hz and 1 Hz (>> 0.02Hz !). To the ear, however, such differences are insignificant. Our frequency accuracies are thus acceptable. The video signal timing was precise and accurate. Thus, there is absolutely no problem with the TV screen refresh.
How We Enforced Safety in the Design As we were using power from the mains, we had to make sure that we were doing everything on the ESD mat just in case charges build up somewhere. We made a cover for the keyboard (as shown in the pictures) so that the player would not come into contact with any of the wires. We connected the ground of both MEGA32 chips together on the keyboard so that there would not be a mismatch in ground potentials.
Interference with Other People’s Designs There was no direct interference with other people’s designs, but our interference concern in this project was that our audio output might disturb those working around us. Thus, we tried to keep the volume down whenever possible.
Usability of our Project The video portion of the project was built based on the idea of interactive learning. To cater to people of all ages learning music, the music stave and notes are drawn large and clear so that they may be easily recognizable. The menu options are also simple and controlled with only 2 pushbuttons, YY and XX. The menu options are also displayed on screen in the Music Notes display mode. In addition, detailed instructions for the pushbuttons and HyperTerm menu functions are also written clearly on the project setup cover for the user’s easy reference. The video portion of our design is thus quite user friendly. However, because our keyboard is small compared to the ones on the market, people with broader fingers may find it difficult to play running notes on the keyboard.
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