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The Integrated Theremin combines five of our boards into one. The boards included are:

  • MiniDuino
    • 16 MHz ATMega 328 processor
    • Arduino UNO Code and IDE Compatible
    • TFT Display connector
    • USB Interface
    • Board is not powerable from FTDI
  • HV Digital Pots
    • 10-bits, 1024 steps
    • Control Frequency and Voltage
  • AudioAmp386
    • 3/4 Watt Output
    • Standard RCA phone style connector
  • XR-2206 Voltage Controlled Oscillator
    • Waveform Adjustment pot from X3 version of XR-2206

Additional Features

The board has additional features including:

  • Advanced Power Supply Design
    • Single +12V power supply input
    • +5V High-Efficiency Switcher to drive logic and High Intensity IR Sensors
      • Previous (separate board) design had a hot regulator on the MiniDuino
        • Due to the current drop of the +12V or +9V to 5V
          • At 200 mA due to the IR sensor cards
      • Total power Measured at 12V, 130 mA =  1.6 Watts
  • Dedicated connectors for IR Sensors
  • Direct (DC) coupling for Voltage Controlled Oscillator to Audio Amplifier
    • AC cap in series with the previous design led to clipping of the audio
  • Added connection to allow Microprocessor to monitor (via A/D) the VCO level for smoother volume control transitions
    • Write all of the D/A serial bits then cycle the FSYNC line to load the D/A
    • Voltage divider
      • Average voltage into divider is 6V
      • Divider resistors 2.2K, 4.7K
      • Divider ratio is (2.2/(2.2+4.7)) = 0.31884
      • 6V * divider ratio = 1.913 V
      • 1.913V * (1023 counts/5V) =  391 counts
      • Peak voltage is 12V - scales to 3.82V which is safely below the 5V input of the A/D
    • Measurements:
      • Minimum count = 278
      • Maximum count = 414
      • Average count = 346
    • Measured the average voltage and it wasn't 6V as expected, it was 5.3V which correlates well to the 346 count
    • Where is the transition supposed to happen with respect to the waveform to write data to the pots? 
    • A/D sample rate is around 10K samples/sec
    • If the max freq is 1KHz that means that the waveform is only sampled 10 times per cycle so there could be a large step in volume
    • Start up question as well - the board needs to be autocalibrated at startup
    • May need hardware assist to cycle FSYNC at zero crossing
    • May want to connect the data and clock to the MOSI and SCK lines instead of PIO lines to speed up transfers
    • May want to use logic analyzer to debug
  • Board layout is slightly under 50 mm x 100 mm to use SeeedStudio service ($30 for 10 pcs).
  • Board has four mounting holes
  • New schematic design using hierarchical sheets
  • Split Power and ground planes (+12V/+5V) at center of card with jumper to connect GNDs

Block Diagram



J1 - Power Connector

  1. +12V
  2. Ground

J2 -Analog Output - RCA connector

J3 -USB-B Mini

J4 - 5-Way Switch

  1. Ground
  2. Voltage (+5V)
  3. Signal (Keypad)

J5 -Volume GVVS

  1. Ground
  2. Emitter Voltage (5V @ 100 mA)
  3. Sensor Voltage
  4. Sensor Output

J6 - Frequency GVVS

  1. Ground
  2. Emitter Voltage (5V @ 100 mA)
  3. Sensor Voltage
  4. Sensor Output

J7 -Analog Spares

  1. AD5
  2. AD4
  3. AREF
  4. GND
  5. AREF
  6. VCC


  1. VCC
  2. Backlight (GND)
  3. RESET
  4. RS
  5. MISO
  6. MOSI
  7. SCK
  8. LCDCS
  9. SDCS
  10. GND

J9(X2)/J10(X1) - Ground jumper

1-2 - GND to GNDA

RV1 - Waveform Adjust

Supported Peripherals

LCD screen.png