Key Pad Musical Synthesizer
Trevor Lager
Brandon Gong
Overview
• Plays Notes when keypad is pressed
• Records notes for playback on SRAM
• Plays back recorded song
Schematic
Components
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SSMI Board
10 kΩ Resistor pack
1.5 kΩ Resistor pack
Keypad
D/A converter (MCP4921 E/P)
SRAM (23LC512)
AUX Output / Speakers
Potentiometer
Resistors and Capacitors for Low Pass Filter
8 Bit Waveform
12 Bit Waveform
Pseudocode
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function Main
Init function
Loop Forever
opMode <- Get operation mode from user
if(opMode == Record)
key <- Get user input from keyboard
playSound(key)
saveToSRAM(key)
else
address = 0
while(not end of song)
key <- getFromSRAM(address)
playSound(key)
address <- next address
End while
End if
End Loop
End Main
Pseudocode
20. function init
21.
Initialize SPI system for SRAM system
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- Max of 20 MHz clock
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- Active High clock
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- First SCK edge
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- LSB first
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Initialize Pin IO
27.
- Input from keyboard
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- Input from mode select
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- Output to speaker
30.
- Com with SPI
31.
Initialize Output compare system to generate notes based on
frequency
32. End init
Pseudocode
33. function playSound(key)
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Frequency <- Notes[key] // Get the frequency based on what key is pressed
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Delay <- conversion from frequency to uS
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For( value = 0; value < 31.4; value += 0.1)
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writeToDAC(digitalSin(value))
38.
Delay
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End Loop
40. End playSound
41. Function writeToDAC(value)
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Select DAC
43.
Send Write command
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Write value
45.
Deselect DAC
46. End writeToDAC
Pseudocode
47. function saveToSRAM(key)
48.
Send write instruction
49.
Send Address // this should start at 0 at the beginning of the
program
50.
Send key
51.
Increment Address
52. End saveToSRAM
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54. function getFromSRAM(address) returns char
55.
Send read instruction
56.
Send address
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return content of address
58. End getFromSRAM
Timing Diagram (Write)
Timing Diagram (Read)
Potential Future Improvements
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Multiple tones
Implement timing for rests
Potentiometer for modulation
Be able to play and playback simultaneously
Question?