Piano Touch Keys II P13364 Team Members: Ed Mackowiak (CE), Whitney - - PowerPoint PPT Presentation

Piano Touch Keys II

P13364

Team Members: Ed Mackowiak (CE), Whitney Zack (CE), Bruce Kynoch (EE), Alex Coleman (EE) Customer/Guide: Gerald Garavuso

Background / Customer Requirements

• Augment a keyboard to allow musical

parameters (pitch, timbre, intensity) to be changed while playing with two hands.

• Allow the musician to play in a way that isn't

possible on currently available keyboards.

• At least two axes of control, tracking both

position and velocity.

• Demonstrate this functionality on a single

keyboard octave.

• Customer Needs

Hardware / Software Design

Capacitive Touch Prototype

• Test board to demonstrate capacitive touch

being read by the MSP430.

• Test Board Demo Video

PCB Design (Key Design)

• Each piano key has:

○ MSP430 IC ○ 1 uF capacitor VDD to GND ○ 6-pin ZIF Connector ○ Touchpad array

• MSP430 and cap on the underside (top

layer, red) of the board.

• Pad array and connector on the top surface

(bottom layer, blue)

• Limited ground-plane on the touchpad layer,

but no ungrounded islands.

PCB Design (Black Key)

Chip side Pad side

PCB Design (White Key)

Chip side Pad side

PCB Design (Reflection)

• One trace was left unrouted.
• A smaller package size might have allowed

for more spacing between the electrode traces and the data lines.

• "No-tent" vias should have been used to

allow for complete solder-mask coverage

• ver the pads.
• A debug LED on the header boards would

have been useful.

• TEST/RST pins should have been tied to

VDD/GND.

Touch Processor (MSP430)

• Collects capacitance data from electrodes.
• Using the capacitance data, a location is

determined.

• A baseline level is regularly updated to

mitigate the effect of uneven trace length.

• The touch processor must be ready to send

the location data over the I2C bus, which is polled at 100 Hz.

Capacitive Technology

Touch Controller Code (MSP430)

MSP430 Reflections

• Baseline calculation algorithm could be

refined.

• Having different pinouts for every white key

design made multiple versions of the code necessary.

I2C Communication

• Bus protocol consisting of one master and

several slaves.

• Supervisory processor acts as master,

polling the individual key processors for X and Y touch data.

• Spent some time debugging the I2C

communication between the mbed and MSP430

• Bus runs at 100kHz

Octave Controller (mBed)

• Communicates with the 12 MSP430s over

the I2C bus. Polls at 100 Hz.

• X/Y data is packaged into a MIDI signal

using MIDI continuous controls, which is then sent to a PC over USB, using the HID MIDI page.

• Debug LEDs indicate proper operation of the

mBed, and also light up if some of the keys are non-responsive.

mBed Reflections

• It is possible to merge the keyboard MIDI

stream with the touch sensor data the mbed level, however this would required a fair amount of extra effort and would not have provided any benefits.

○ Still would need two cables (one for keyboard power, and one for combined mbed power/data)

Sound Generation (Plogue)

• Takes in MIDI signals from the keyboard and

the mBed.

• Frequency and Intensity are extracted from

the keyboard notes.

• X and Y are extracted from the mBed MIDI

channel.

• New Frequency = Old Frequency + K*Y
• K is a scaling factor
• 50 ms smoothing factor to control jitter

Plogue Reflections

• Pitch shifting should be relative to the initial

keypress position.

• Lots of flexibility in sound generation options

○ MIDI soundbank ○ Custom synthesizers

• Once design is finalized, it can be packaged

into a custom Bidule for possible distribution.

Bill of Materials

Part(s) Cost mBed FREE ($60 production) PCB $112.55 Connectors & passive components $124.48 Total $237.03 Vendor List Digikey mBed OSH Park

Bill of Materials