FREQUENCY
KEYBOARD
Braeden Lieberman
Nathan West
Project Overview
• Goal
• Use frequency to allow user to change the state of a digital system
• Create characters based on the frequency
• What we did
• Take input signals from a function generator
• Digitize the analog signals using band pass filters
• Display characters based on digital value on LED matrix
• Change the character by increasing the frequency
Two Subsystems
• Frequency Analyzer (MSGEQ7)
• Analyze frequency and digitize the value from 0 to 7
• Increment character index if increase in frequency is detected.
• Display (LED matrix)
• Uses character index to display corresponding character on a
cursor
• If push button is pressed, LED matrix will save current character
and increment the cursor.
FREQUENCY
SUBSYSTEM
MSGEQ7
• Mounted on Sparkfun’s Spectrum Shield for Arduino
• Contains 7 band pass filters
• Uses a multiplexer to choose a band pass filter
• Uses a strobe pin to change which band pass filter is in
use
• Outputs a DC value based on the input frequency and
filter
Block Diagram
Schematic (Wiring to MSGEQ7)
*schematic acquired from
https://www.sparkfun.com/products/10306
Schematic (MSGEQ7 on Shield)
*schematic acquired from
https://www.sparkfun.com/products/10306
Frequency Response
• Bandwidths are actually different for each band pass filter
MSGEQ7 Timing Diagram
Retrieving Data from MSGEQ7
Tmin = 72 usec
PseudoCode for Frequency Subsystem
• Strobe reset, i = 0
• While int i < 7
• Strobe strobe pin
• Read DC ourput (store in variable val)
• i++
• If val > val_old, assign character_index to I
• val_old = val;
• If character_index > old_index, increment character to be
displayed on LED matrix
• old_index = current_index;
DISPLAY SUBSYSTEM
LED Matrix
• Matrix contains 8 shift registers
• 80 bits of storage each
• Data entered into a latch register
• Data is shifted in 1 bit at a time
• Latch register transferred into desired row
• Only one row is displayed at a time
• Used bit-banging instead SCI
• Implemented in RTI system for precise and quick timing
• Bi-color LEDs, had to choose one color due to memory
constraints
Schematic
LED Timing Diagrams
Shifting To LED Matrix
• Active low logic for LED’s
• To shift in red LED, R1 is low, G1 is high
Latching data into a row
• En must be low
• Select Row with pins A, B, C using binary representation
• To latch to row 3…
• Pull Enable low
• Set pins ABC = 011
• Pulse L pin
• Pull Enable high
LED Timing Diagrams
Shifting To LED Matrix
Latching data into a row
Cursor
• Divided matrix into 8 8X8 character matrices/cursors
• Had to use char to decrease memory usage
• Dropped memory usage of arrays by 1kB from integer array
• Allowed LEDs to be selected based on row and column
location
• Used case statements to determine which cursor was
selected
• A pushbutton was used to increment the cursor
PseudoCode for Display
If time_index = 100,
• Time index = 0
• Assign current block at cursor index to desired character. (i.e. if
cursor index is 0 the far left block of LED matrix will display current
character)
• Load information stored in each block onto the LED matrix one row
at a time
• Select row and Latch information into corresponding row on LED
for i = 0; i < 7; i++,
Select Row
Make En signal High
Delay 50 microseconds
time_index++
Project Status
• Current State of Design
• Will display characters on the matrix
• Changes when frequency is increased
• Problems Faced
• Noise
• Delay/timing
• Future plans/implementation
• Add a second function generator
• Have it display characters based on music
• Have the characters be sent to the computer
Questions