Signal processing and conditioning

The original output from Steve's system had a DC offset, noise from the power line and an overwhelming range. These need to be processed and conditioned.

First graph shows the response of touch without filtering. The second graph shows the bassline noise of the original signal.

Signal conditioning had been done including smoothing and offsetting. Since capacitive sensing setup use several antanas which could be affected by 50hz power line interference. A first order software low pass filter had been applied. Cut off at 50hz. A moving average filter with a 5 data window is used to average the data when an interaction occurs. The data was directed mapped to midi (0-127) and bassline (no contact set data to 0) had been offered according to the experiment. In order to keep the midi at the same note when there is no new interaction made, the new midi note will be sent only when data is changed. Finally the two midi information will be sent through serial - note and velocity - both map to the time data. A longer time will result in a louder higher note.

The last graph shows the result after conditioning. The touch can be sensed up to 5 fingers. And the bassline noise had been removed.