SYNTH-VCO-01

Features

• Build of Pico VCO by HAGIWO
• Digital Voltage Controlled Oscillator (VCO)
• Three modes: Wavefold, FM and AM
• PWM output with 2 pole low pass filter
• Each mode has eight built-in waveforms
• XIAO RP2040 CPU
• (5) Pushbuttons
  • Octave Up/Down
  • Mode Up/Down (Wavefold, FM and AM)
  • Push Timbre switches between 8 waveforms
• (2) Knobs
  • Freq fine adjust
  • Mod adjust
• Standard EuroRack 16 pin header
  • Supports 12V in with on-board 5V regulator
  • 5V regulator can be not installed if 5V is available on EuroRack connection
• Card is not a Eurorack card
  • Probably too deep, needs cabling
• (4) 6-32 mounting holes
  • Stacks with SYNTH-MIDI-CTL-01 card

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

Software

• SYNTHVCO01 Arduino Code

Checkout/Testing

• Nice sine wave
• Very little noise

• 1.61V is close to Middle-C with FREQ_POT straight up
• Get close with scope set on HFR coupling to reject the PWM carrier
• Tune with and listen for beat
• Three Octaves of C | Sine Waves - Good for octave step test

MOD_CV	FREQ_CV	MOD_POT	FREQ_POT	MODE_SW	OCT_SW	MEASURE (Hz)	SIGN TYPE
0	0	CCW	CCW	CENTER	CENTER	70.5	SINE
0	0	CCW	CCW	UP	CENTER	66	WAVEY-SAW
0	0	CCW	CCW	UP	CENTER	70.5	SAW
0	0	CCW	CCW	CENTER	DOWN	35.4	SINE
0	0	CCW	CCW	CENTER	UP	141.6	SINE
0	0	CCW	CCW	CENTER	CENTER	70.5	SINE
1	0	CCW	CCW	CENTER	CENTER	142.9	SINE
2	0	CCW	CCW	CENTER	CENTER	293.4	SINE
3	0	CCW	CCW	CENTER	CENTER	598.4	SINE
4	0	CCW	CCW	CENTER	CENTER	1200	SINE
5	0	CCW	CCW	CENTER	CENTER	2441	SINE
5	0	CCW	CCW	CENTER	UP	4880	SINE

Issues

Rev 1

• Working/no functional issues
• Mode/Oct switches s/b 3 way toggle with center off
• R13 s/s has 330K, s/b 33K
• R14 s/s has 220K, s/b 22K
• C6 s/s hard to see
• OpAmp U2 uses wrong schematic symbol
  • ADD WIRE U2-1 TO U2-6 (VOUT) ON REAR
  • ADD WIRE U2-7 TO U2-5 (VCC) ON REAR
  • LIFT IC U2-2
  • LIFT IC U2-4
  • ADD WIRE IC U2-2 TO SOCKET U2-4
  • ADD WIRE IC U2-4 TO SOCKET U2-2
• Works with rework

Assembly Sheet

• SYNTH-VCO-01 Rev 1 Assembly Sheet