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Wireless Guitar Effects Processor

Wireless Guitar Effects Processor. ECE 345: Senior Design April 26, 2001. Group 26: Jeff Johnisee Ken Schutte Scott VanDyke. Objectives. Implement wireless transmission to increase mobility on stage and decrease number of cables in stage set-up

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Wireless Guitar Effects Processor

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  1. Wireless Guitar Effects Processor ECE 345: Senior Design April 26, 2001 Group 26: Jeff Johnisee Ken Schutte Scott VanDyke

  2. Objectives • Implement wireless transmission to increase mobility on stage and decrease number of cables in stage set-up • Provide hands-free method to choose effect and modify its parameters • Construct simple modules to enclose circuitry and produce a marketable product

  3. System Overview TI 54x DSP A/D D/A serial Transmitter Reciever Amp HC12 A/D Guitar Amp ElectricGuitar Roland EV-5

  4. Initial DSP Plan • Reverberation • Using Comb and All-Pass Filters • Phasing • Using 4 Oscillating All-Pass filters • 4-tap Delay • Using 5 Delay Buffers

  5. DSP Implementation • Reverberation • 4 All-Pass Filters in Series • Phasing • Using 1 Oscillating All-Pass filters • 4-tap Delay • No Change

  6. Block Diagram of All Pass Filter Frequency Response Input g Z-N g Output

  7. Block Diagram of Phaser 1-mix Input output All Pass mix LFO

  8. Phaser Specifications • All Pass Delay (varying) • 1 – 255 Samples (0 - .0059 Seconds) • Phase Length (user varying) • 0.75 – 16.2 Seconds • All Pass Gain • 0.625

  9. Impulse Response

  10. Block Diagram of 4-Tap Delay

  11. 4-Tap Delay Specifications • Delay Line Lengths (real time user varying) • 0 - 65535 Samples (0 – 1.5 Seconds) • 0 - 32768 Samples (0 - .75 Seconds) • 0 - 16384 Samples (0 - .375 Seconds) • 0 - 8192 Samples (0 - .186 Seconds) • Delay Taps • 0.75 • 0.6 • 0.5 • 0.4 • Decay (real time user varying) • 0.5

  12. Impulse Response

  13. Block Diagram of Reverb 1-mix Input output AP AP AP AP mix decay

  14. Reverb Specifications • Delay Line Lengths • 840 Samples (.02 Seconds) • 636 Samples (.015 Seconds) • 2248 Samples (.05 Seconds) • 1644 Samples (.04 Seconds) • All Pass Gain (real time user varying) • ~0 - 0.625 (AP1, AP2) • ~0 - 0.750 (AP3, AP4) • Decay (real time user varying) • ~0 - 0.50 • Mix • 0.50

  15. Impulse Response

  16. Signal Amplification • Electric guitar output • full volume  200-300mV • peaked around 500mV • constant 35-40mV noise

  17. Amplifier Circuit: basic audio pre-amp

  18. Amplifier Frequency ResponseVout p-p vs. input frequency for 100mV p-p sine wave

  19. Initial design: Build simple AM transmitter / receiver Adjust sensitivity to fit guitar audio spectrum Simplicity would make troubleshooting easier Final design: LINX analog RF chips ¼ wave whip antennas Separate containers if time permits WIRELESS DESIGN

  20. FM mod / demod for analog signals. 8-channel binary selective operating freq. In 902-920 MHZ band. 2.7-16V DC supply voltage range. Module design includes VCO(oscillator) only requires antenna and power. Designed for high-quality wireless audio. Covers 50HZ – 25kHZ audio band. Relatively low cost, pair around $60. LINX HP-II 900MHZ TRANSMITTER / RECEIVER PAIR

  21. FM MODULATION • LPF shapes signal to 25kHz BW • VCXO serves as freq. reference and is directly mod. • PLLlocks on to phase and sets Tx freq. According to chan. sel. Lines. • Microcontroller sets CTS high.

  22. FM DEMODULATION • SAW BPR for unwanted RF energy not in BW. • LNA increases receiver sensitivity and lowers noise. • IF receiver strip converts the signal to 2 IF levels and performs the demodulation. • Active LPF cleans up audio signal. • RSSI is set high when signal strength is good.

  23. WIRELESS SYSTEM LAYOUT

  24. Signal strength (dBm) in red. Noise strength (dBm) in blue. SNR = 9.875. Noise floor evident in transmitted audio. SNR OF Tx / Rx PAIR

  25. OVERALL PERFORMANCE OF WIRELESS SYSTEM • Considering: • Small percentage of wireless project success • Small signal strength and BW of guitar signal • Very satisfied with audio quality! • Noise heard from amp could also be attributed to: • Guitar grounding problem • Poor jack connection on amp

  26. HC12 Microcontroller • Interface between user controls and DSP • Monitors selection buttons • Reads controller pedal through A/D • Activates status LEDs

  27. Roland EV-5 controller pedal • Acts as variable voltage source • Pedal sweeps between Vmin and Vcc • Side knob controls Vmin • Sent to A/D and represented by 8 bit value

  28. Serial Communication • One byte specifies effect and control level A5 A4 A3 A2 A1 A0 S1 S0

  29. Serial Set-up: The HC12 SCI • Baud Rate Control Register • SCI Baud Rate = MCLK/(16*SBR) • 8MHz clk, 9600 bps  SBR = 0x34 • SCI Control Registers • Enable transmitter, reciever SC0CR2 = 0x0C • One stop bit, eight data, no parity  SC0CR1 = 0x00

  30. Serial Set-up: TI EVM320C549 • TL16C550 Serial Controller • Configured in core.asm code • Accessible Registers • LCR = 0x03 : 8 data bits, 1 stop bit, no parity • Baud Rate Generator: divisor for 3.6864MHz • 3686400/N = 16*(9600 bps)  N = 24 • MCR = 0x01 : Data terminal ready

  31. Problems and Obstacles • Wireless design • RF interference • Signal strength • HC12 • Chip problems • Serial interface • DSP • Reducing noise • Output quality

  32. Audio quality of effects Wireless audio HC12 control Production of finalized product Successes

  33. If we had more time… • Integration of DSP and controller boxes • Manufacture printed circuit board • Development of more elegant and user-friendly power supplies

  34. Questions?

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