Theremin Sensor Controller IP - fpga-theremin/theremin GitHub Wiki

Requirements

• Low latency (<= 1 sample interval - 1/48000 of second)
• High precision and sensitivity
• AXI4Lite interface with PS (CPU)

Oscillator output

Oscillator output is 3'3V logic level signal with duty cycle near to 50%.

The goal of theremin sensor is to convert oscillator frequency to:

• note number and note frequency for pitch antenna signal
• volume multiplier for volume antenna

Pitch antenna signal processing stages

• Measure signal period
• Moving average filter with adjustable window length (1..1024)
• Scale to 000000..FFFFFF range for working range of hand distance, clamp to 000000 or FFFFFF if distance exceeds range
• Convert scaled period value to distance from hand to antenna using lookup table and linear interpolation
• Convert distance to note number using lookup table and interpolation
• Convert note number to pitch phase increment (fractional part of 0x1000000 of phase increment for single sample) - lookup table and interpolation

Volume antenna signal processing stages

• Measure signal period
• Moving average filter with adjustable window length (1..1024)
• Scale to 000000..FFFFFF range for working range of hand distance, clamp to 000000 or FFFFFF if distance exceeds range
• Convert scaled period value to distance from hand to antenna using lookup table and linear interpolation
• Convert distance to volume multiplier