A basic and generic VCO based on SSI2131
| Name | Type | Description |
|---|---|---|
coarse |
Potentiometer | |
fine |
Potentiometer | |
freq LED |
Bi-color LED | Voltage value for tri, green for positive voltage, red for negative voltage |
pulse width |
Potentiometer | Almost full-range (0% ~ 100%) pulse width control of pulse |
fm amt |
Potentiometer | fm amount |
pulse amt |
Potentiometer | pwm amount |
lfm |
Switch button | FM type for fm, exponential (off) or linear (on) |
lfm LED |
LED | Blue LED indicates if lfm switched on |
soft |
Switch button | Sync type for sync, hard (off) or soft (on) |
soft LED |
LED | Blue LED indicates if soft switched on |
lfo/osc |
Toggle switch | Switch between oscillator mode and LFO mode |
There are 3 rheostats on the PCB panel
| Name | Description |
|---|---|
VR_SCALE |
Adjust frequency range (scale) for SSI2131 |
VR_HFT |
Adjust high frequency compensation for SSI2131's exponential converter |
VR_SINE |
Adjust sine shaper in tri-to-sine circuit |
| Name | Type | Vmin | Vmax | Description |
|---|---|---|---|---|
v/oct |
Input | 0V | +10V | |
fm |
Input | -5V | +5V | |
sync |
Input | -5V | +5V | Oscillator synchronization input, triggers on rising edge |
pwm |
Input | -5V | +5V | Pulse width modulation, only apply for pulse |
| Name | Type | Vmin | Vmax | Description |
|---|---|---|---|---|
sine |
Output | -5V | +5V | Sine wave |
tri |
Output | -5V | +5V | Triangle wave |
saw |
Output | -5V | +5V | Downward sawtooth wave |
pulse |
Output | -5V | +5V | Pulse wave |
- Height: 128.5mm (3U)
- Width: 40.3mm (8hp)
- Depth: 36mm
+12V: 38mA-12V: 24mA+5V: N/A
Soft sync synchronizes the SSI2131 to an external signal when the triangle waveform is falling and close to GND. A capacitively-coupled pulse on the SOFT SYNC input will cause the triangle to switch from falling to rising. If the voltage on TCAP is too high then synchronization will not take place. The synchronization is “soft” in that it only occurs within a narrow part of the oscillating cycle; at all other times it has no effect.
—— From SSI2131 datasheet, Page 6 - 7, SYNCHRONIZATION.
Blank panel design files in various file formats are provided. Drill holes are filled in black, soldering mask are filled in grey.
Available file formats:
| Format | Software / Toolchain |
|---|---|
.afdesign |
Affinity Designer 2.6.5 (My main design tool) |
.svg, .dxf |
Affinity Designer 2.6.5 |
.ai |
Adobe Illustrator 2022 |
FAREKIND VIRTUAL ASSETS, May 2025.