Receives MIDI CC messages via TRS input and outputs analog voltage for guitar pedal expression inputs.
ATtiny1614 (SOIC-14)
- 16 KB flash, 2 KB RAM
- Hardware UART (31.25 kbaud MIDI)
- Built-in 8-bit DAC (direct analog output, no external DAC or filtered PWM needed)
- Requires SOIC-to-DIP adapter for breadboard prototyping
H11L1M schmitt-trigger optocoupler
TRS Tip ──── 220Ω ──── Pin 1 (anode)
TRS Sleeve ────────── Pin 2 (cathode)
1N4148 across pins 1–2 (cathode to pin 1)
Pin 4 (VCC) ───────── +5V
Pin 5 (GND) ───────── GND
Pin 6 (output) ─┬──── 10kΩ pullup to VCC
└──── ATtiny RX pin
Note: Output is inverted. Verify TRS Type A vs B pinout for your MIDI source.
3.5mm TRS jack
- Tip: DAC output (via optional 10kΩ series resistor for protection)
- Ring: VCC (3.3V or 5V depending on pedal)
- Sleeve: GND
Note: Verify your pedal's expression input pinout—varies by manufacturer.
- DC barrel jack (2.1mm center-positive)
- 5V regulated (7805 or LDO if input >5V, or direct 5V supply)
- 100µF + 0.1µF decoupling at regulator
- 0.1µF decoupling at ATtiny VCC pin
| Component | Value/Part | Qty |
|---|---|---|
| MCU | ATtiny1614 | 1 |
| Adapter | SOIC-14 to DIP | 1 |
| Optocoupler | H11L1M | 1 |
| Diode | 1N4148 | 1 |
| Resistor | 220Ω | 1 |
| Resistor | 10kΩ | 2 |
| Capacitor | 100µF electrolytic | 1 |
| Capacitor | 0.1µF ceramic | 2 |
| Regulator | 7805 or LDO | 1 |
| Jack | 3.5mm TRS (MIDI in) | 1 |
| Jack | 3.5mm TRS (expr out) | 1 |
| Jack | DC barrel 2.1mm | 1 |
Optional:
- LED + 330Ω (MIDI activity)
- TVS diode / polyfuse (power protection)
- UPDI interface (single pin)
- Use dedicated UPDI programmer or SerialUPDI with USB-serial adapter
- Initialize UART at 31.25 kbaud
- Initialize DAC output
- Parse incoming MIDI bytes for CC messages
- Map CC value (0–127) to DAC output (0–255)
- Optional: filter for specific CC number / channel