SwampThing

Beginning of a standalone Juno-106 inspired DCO monosynth for UF AES. Built around Raspberry Pi Pico Microcontroller.

Project Status

Component	Designed	Prototyped	PCB / Finalized
DCO Saw-core	X	X
DCO Pulse / PWM	X	X
DCO SUB	X
Blend	X
MIDI USB	X	X
MIDI DIN
VCF	X
EG	X
VCA	X
Power Solution
Output

Table of Contents

• Installation / Build
  • Prereqs
  • Build Steps
  • Quick Build & Flash
  • Manual Flashing
  • I/O Notes
• Architecture
  • Component Diagram
  • MIDI
    • USB MIDI
    • DIN MIDI
  • Digitally Controlled Oscillator (DCO)
    • SAW
    • PULSE / PWM
    • SUB OSC
    • BLEND
  • Envelope Generator (EG)
  • Voltage Controlled Amplifier (VCA)
  • Voltage Controlled Filter (VCF)
  • Power Solution
• Incomplete BOM

Installation / Build

MIDI control, oscillator reset signals, charge voltage and envelope gates are derived from a Raspberry Pi Pico.

Prereqs

• VS Code
• Raspberry Pi Pico VS Code Extension

Build Steps

1. Clone this repo
2. Open the src folder in VS Code (not the root folder!)
3. Open a PowerShell terminal in VS Code
4. Run:

mkdir build
cd build
cmake -G "Ninja" ..
cmake --build .

5. The .uf2 file will be in build/SwampThing.uf2

Quick Build & Flash

• Press Ctrl+Shift+B to build and flash in one step - nifty!

Manual Flashing

1. Hold BOOTSEL on your Pico and plug it in
2. Drag SwampThing.uf2 onto the Pico drive

I/O Notes:

Function	GPIO #
Clock output	13
CV output	14
Gate output	12

Architecture

Component Diagram:

MIDI:

USB MIDI (Implemented)

SwampThing appears as a class-compliant USB MIDI device over the Pico’s micro-USB port using TinyUSB.

DIN MIDI (Planned)

5-pin DIN MIDI IN (with opto-isolation and UART at 31.25 kbps) is planned. DIN and USB MIDI will eventually share the same internal note/gate handling.

Digitally Controlled Oscillator (DCO):

SAW

Juno-style ramp core. A TL074 op-amp integrator generates a rising ramp, NPN transistor reset discharges the timing capacitor at a rate set by the microcontroller clock. Pitch is set by the reset clock (GPIO 13). Ramp slope is set by a PWM-derived charge voltage filtered to DC (GPIO 14).

PULSE / PWM

Saw --> Comparator, threshold = PWM

SUB OSC

OSC --> Flip Flop, halves frequency

BLEND

Blend control between saw and pwm

Envelope Generator (EG):

Currently In Development

Design chosen

Voltage Conrolled Amplifier (VCA):

Currently In Development

JFET implementation

Voltage Controlled Filter (VCF):

Currently In Development

Based on Mortiz Klein / Erica Synths VCF

Power Solution:

Currently In Development

Presently planning +/- 12V, 5V rails.

Incomplete BOM:

PART	QTY	NOTE
Raspberry Pi Pico	1	Micrcontroller
TL074	1	4x Op Amp
2N3904 NPN BJT	1	Reset Transistor