ER-VCO-03

Features

• Build of Pico VCO by HAGIWO
  • Prototyped on SYNTH-VCO-01 - Synth Voltage Controlled Oscillator
• Digital Voltage Controlled Oscillator (VCO)
• Eurorack 3U tall, 6HP wide (30 mm)
• (3) Card set
• XIAO RP2040 CPU
• Three modes: Wavefold, FM and AM
• PWM output with 2 pole low pass filter
• Each mode has eight built-in waveforms
• AC coupled output
• (3) Switches
  • 3-position Octave Up/Down toggle
  • 3-position Mode Up/Down toggle (Wavefold, FM and AM)
  • Timbre Pushbutton switches between 8 waveforms
• (2) Knobs
  • Freq fine adjust (sub octave range)
  • Mod adjust
• Standard EuroRack 16 pin power header
  • Uses 5V from Eurorack power
• Views (left to right)
  • Front Panel
  • Control Panel controls side
  • Control Panel rear side
  • Logic card rear side
  • Logic card component side (faces rear of card set)

XIAO RP2040 Pins

• Pin 1, GP26 = Vol/Oct, Analog In
• Pin 2, GP27 = Freq Pot, Analog In
• Pin 3, GP28 = Mod, Analog In
• Pin 4, GP29 = Mod Pot, Analog In
• Pin 5, GP6 = Timbre Pushbutton, select waveform type, Digital Input
• Pin 6, GP7 = Gate (optional), Digital Input
• Pin 8, GP1 = Octave Down, Digital Input
• Pin 9, GP2 = Audio Output, PWM out
• Pin 10, GP4 = Mode Down, Digital Input
• Pin 11, GP3 = Mode Up, Digital Input
• Pin 12 = +3.3V
• Pin 13 = GND
• Pin 14 = +5V

Cards

• Three card set
  • Front Panel
  • Controls
  • Processor

Front Panel Card

• 3U tall, 6 HP wide
  • 128.4mmx30mm
• Holes for 2 Pots, 4 Jacks, 1 Pushbutton, 2 Toggles
• Could use for other designs
• Re-label with White-on-Black P-Touch labels

Controls Card

• 30mmx76mm
• Pots, Jacks, Pushbutton fit through Front Panel
• Lower right Jack - Output line
• (3) Digital Input jacks
  • Scale resistors reduce 5V signals to 3V
  • Clamping diodes protect inputs
  • Filter cap for noise reduction
• (2) Pots are analog inputs to Processor card
  • Filtered inputs to make pots "cleaner"
• Headers for External Toggles
• 2x8 Female Header Socket connects to Processor Card
  • Pinout

1. Vcc
2. Vcc
3. N/C
4. Oct Down Toggle (external)
5. Mod Pot
6. Oct Up toggle (external)
7. Gate input
8. Mode Up Toggle (external)
9. Frequency adjust Pot
10. Mode Down Toggle (external)
11. Volts per Octave CV Analog input
12. Modulation CV input
13. Audio Out
14. Timbre Pushbutton
15. GND
16. GND

Processor Card

• 30mmx76mm
• XIAO RP2040 CPU
• PWM output with 2-pole filter
• Audio Amp/Driver
• Eurorack 10 pin header
  • Uses +12
• On-board 5V regulator
• 2x8 Male Header connects to Controls card
  • Pinout

1. Vcc
2. Vcc
3. N/C
4. Oct Down Toggle (external)
5. Mod Pot
6. Oct Up toggle (external)
7. Gate input
8. Mode Up Toggle (external)
9. Frequency adjust Pot
10. Mode Down Toggle (external)
11. Volts per Octave CV Analog input
12. Modulation CV input
13. Audio Out
14. Timbre Pushbutton
15. GND
16. GND

Software

• SYNTHVCO03.ino
  • Inverts analog inputs for pots (1023-value) to match Rev 1 PCB

Issues

Rev 2

• Daughtercard (CPU)
  • Move U3 ref des Silkscreen
  • Rotate CPU - USB pointing up less slot intrusion
    • No more USB jack collision with 10-pin power jack
  • Change from 30mm to 29mm wide
  • Add Rev 2 marking to Silkscreen
• Controls card
  • Change from 30mm to 29mm wide
  • Rotated pots 90 deg so half is pointing up
  • Some tracks/layers improvements
  • Improved 5V pour - adjusted down to CPU

Rev 1

• Working
  • MODE pushbutton works
  • MOD CV works
  • FREQ 1V/oct CV works
• Front Panel card
  • WAVE-FORM Pushbutton hole is too small - drilled bigger hole
  • OCTAVE UP/DOWN, MOD UP/DOWN switches holes are too small - drilled bigger holes
• Controls card
  • MOD and FREQ pots are backwards - easily fixed in software
• Control/Daughtercards seem aligned to eac other OK, but skewedto Front Panel
  • Make card 28mm?
• RP2040 hangs over USB side too far (card is wider)
  • Maybe rotate 90 degrees?
• Put 2 toggle switches onto PCB

Assembly Sheet

• SYNTH-VCO-CTL-03 Rev 1 Assembly Sheet - Controls board
• SYNTH-VCO_DB-03 Rev 1 Assembly Sheet - CPU bload