Hardware

1. Senior Project • Electrical Engineering • 2012 DigiTap: Designing and Creating MIDI Compatible Tap Dancing Shoes Jacob LaRocca Advisors: James Hedrick, Palma Catravas Hardware Detection Sensors A 2mm deep channel was milled in each aluminum tap to fit a 3.5mm diameter piezo disc. The pulse shown below is the voltage reading from lightly tapping one of the outfitted taps on the table. The voltages could reach up to 80 volts on a hard tap, and any tap produced a voltage too high for the microcontroller. In order to compensate for this, I created filtering and pulse stretching circuits for each tap. Filtering and Stretching • Schottky Diodes were used in the clamping circuit • An RC filter circuit smoothed out all of the ripples • Monostable 555 timers were used on each pulse to create a square pulse 2ms long Microcontroller and Radio Software • An mBed microcontroller was used for its speed, size, and built-in MIDI library • Much easier to program because it doesn’t use a proprietary language • Xbee radios were used, based on their size, compatibility, and range • Programmed in C • Used a pre-written MIDI library provided by mbed.org Important Functions and Libraries InterruptIn: Instead of using a DigitalIn input pin that reads 1 or 0, this function looks for a rising edge, allowing for more accurate and detection quickly, with less false triggers USBMIDI:The USBMIDI library is coded to transmit standard sets of 8-bit MIDI signals. Some of the signals include NoteOn, NoteOff, Pitch, and Aftertouch. Hardware Setup Code Process The Xbee radio is monitoring continuously at 57600 baud, and reads in single ASCII characters. If the message is ‘A’, ‘B’, ‘C’, or ‘D’, then the mBed sends a MIDI signal to the computer. If the Xbee reads ‘W’, ‘X’, ’Y’, or ‘Z’, the mBedadds 1 to the note values assigned to each tap.