https://github.com/risgk/digital-synth-pra32-u2
PRA32-U2 is a 4 Voice Polyphonic Synthesizer for Raspberry Pi Pico 2/RP2350
https://github.com/risgk/digital-synth-pra32-u2
audio midi pra32 raspberry-pi-pico-2 rp2350 synthesizer
Last synced: 4 months ago
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PRA32-U2 is a 4 Voice Polyphonic Synthesizer for Raspberry Pi Pico 2/RP2350
- Host: GitHub
- URL: https://github.com/risgk/digital-synth-pra32-u2
- Owner: risgk
- License: cc0-1.0
- Created: 2025-01-19T03:11:02.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2026-03-04T12:47:23.000Z (4 months ago)
- Last Synced: 2026-03-04T19:32:50.358Z (4 months ago)
- Topics: audio, midi, pra32, raspberry-pi-pico-2, rp2350, synthesizer
- Language: C
- Homepage: https://risgk.github.io/#digital-synth-pra32-u2
- Size: 15.2 MB
- Stars: 18
- Watchers: 1
- Forks: 2
- Open Issues: 2
-
Metadata Files:
- Readme: README-PRA32-U2-P.md
- License: LICENSE
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README
# Digital Synth PRA32-U2/P (PRA32-U2 with Panel) v2.5.2
- 2026-03-06 ISGK Instruments
-
## PRA32-U2/P (Optional)
- Features
- Editing and displaying parameters by panel operation
- Playing by panel operation
- Built-in monophonic 8-step sequencer
- Panel and Step Sequencer Parameters
- This option requires 1 to 4 SWs (tactile switches), 2 to 3 VRs (ADCs), and a monochrome 128x64 OLED Display based on SSD1306 series drivers
- Tested with Pimoroni Pico Audio Pack, M5Stack MIDI Unit (optional), Long Leg 2x20 Pin Socket * 2, Seeed Studio's Grove Shield for Pi Pico, Dual Button * 3, Rotary Angle Sensor * 3, and an OLED Display 0.96 inch
- Uncomment out `//#define PRA32_U2_USE_CONTROL_PANEL` in "Digital-Synth-PRA32-U2.ino" and modify the constants
- Inputs
- SW0: Prev Key (Push to go to the previous page, Long press to the previous group)
- SW1: Next Key (Push to go to the next page, Long press to the next group)
- SW2: Play Key (Normal Mode: press to play, Sequencer Mode: push to start/stop) (omittable)
- To not use this key, comment out `#define PRA32_U2_KEY_INPUT_PLAY_KEY_PIN (20)` in "Digital-Synth-PRA32-U2.ino"
- SW3: Prog - Key (Long press to change to the previous user program) (optional)
- To use this key, uncomment out `//#define PRA32_U2_KEY_INPUT_PROG_MINUS_KEY_PIN (17)` in "Digital-Synth-PRA32-U2.ino"
- SW4: Prog + Key (Long press to change to the next user program) (optional)
- To use this key, uncomment out `//#define PRA32_U2_KEY_INPUT_PROG_PLUS_KEY_PIN (19)` in "Digital-Synth-PRA32-U2.ino"
- SW5: Shift Key (optional)
- Shift + Prev/Next Key: Go to the previous/next group without long-pressing
- Shift + Prog -/+ Key: Change to the previous/next user program without long-pressing
- Shift + VR0/1/2: Prevent values from changing across 64
- To use this key, uncomment out `//#define PRA32_U2_KEY_INPUT_SHIFT_KEY_PIN (21)` in "Digital-Synth-PRA32-U2.ino"
- VR0 (ADC0): Parameter A
- VR1 (ADC1): Parameter B
- VR2 (ADC2): Parameter C for Play (omittable)
- Panel Play Pitch in Normal Mode, Seq Pitch Ofst (Offset) in Step Sequencer Mode
- To not use this, comment out `#define PRA32_U2_KEY_INPUT_PLAY_KEY_PIN (20)` in "Digital-Synth-PRA32-U2.ino"
- NOTE: Using a USB cable with ferrite cores is recommended to prevent ADCs from being affected by USB MIDI communication noise, and UART MIDI control is also recommended
### GUI Pages
#### Group A
- Synth Parameters
- NOTE: The parameters Filter EG Amt and EG Filter Amt are the same
#### Group B
- Panel Parameters
- Panel Play Mode [Nrm|Seq]: Normal Mode, Step Sequencer Mode
- Panel MIDI Ch: Basic Channel 1-16
- Panel Play Pitch: 0 is Off, 1-4 is lowest, 124-127 is highest
- Panel Play Velo (Velocity)
- Panel Scale [Maj|Min|Mel|MaP|MiP|Chr]: Major, Natural Minor, Ascending Melodic Minor (Jazz Minor), Major Pentatonic, Minor Pentatonic, Chromatic (2 octaves)
- Panel Pitch Ofst (Offset) [-|+]: Offset Panel Play Pitch and Seq Pitch 0-7 (min -60 to max +60)
- For example, if Panel Scale is Maj and Panel Pitch Ofst is -25, the scale is G Mixolydian
- For example, if Panel Scale is Maj and Panel Pitch Ofst is -15, the scale is A Aeolian (Natural Minor)
- For example, if Panel Scale is Maj and Panel Pitch Ofst is +10, the scale is D Dorian
- For example, if Panel Scale is Maj and Panel Pitch Ofst is +20, the scale is E Phrygian
- For example, if Panel Scale is Maj and Panel Pitch Ofst is +25, the scale is F Lydian
- Panel Transpose [-|+]
- For example, if Panel Scale is Mel and Panel Transpose is -3, the scale is A Ascending Melodic Minor (Jazz Minor)
- For example, if Panel Scale is Min and Panel Transpose is -3, the scale is A Natural Minor
- For example, if Panel Scale is MiP and Panel Transpose is -3, the scale is A Minor Pentatonic
- Step Sequencer Parameters
- Seq Step Note [4|8|16]: Quarter Note, Eighth Note, Sixteenth Note
- Seq Clock Src [Int|Ext]: Internal, External (Rx MIDI Clock)
- Seq Pitch Ofst (Offset) [-|+]: Offset Seq Pitch 0-7 (min -60 to max +60)
- Seq T/Rx St/Sp (Transmit/Receive Start/Stop): Off, On
- Seq Tempo: BPM 56-300
- Seq Gate Time [1/6|2/6|3/6|4/6|5/6|6/6]
- Seq Mode [Fwd|Rvs|Bnc]: Forward, Reverse, Bounce
- Seq Num Steps (Number of Steps): 1-32 (current step mod 8 is used as the index for Seq Pitch and Seq Velo)
- Seq On Steps: bit 0 is Step 1 On, ..., bit 6 is Step 7 On (Step 0 is always On)
- Seq Act Steps (Active Steps): bit 0 is Step 1 Active, ..., bit 6 is Step 7 Active (Step 0 is always Active)
- Seq Pitch 0-7: 0 is Off, 1-4 is lowest, 124-127 is highest
- Seq Velo 0-7 (Velocity 0-7)
- Step Sequencer Operations
- Seq Rand Pitch (Randomize Pitch 0-7): Change the value from 0-32 [Rdy] to 96-127 [Exe]
- Seq Rand Velo (Randomize Velo 0-7): Change the value from 0-32 [Rdy] to 96-127 [Exe]
- Control Parameters
- Modulation
- Breath Controller
- Sustain Pedal
- Control Operations
- Panic: Change the value from 0-32 [Rdy] to 96-127 [Exe]
#### Group C
- Write Operations
- Write Program 0-7, Write Panel Prms (Write Panel and Step Sequencer Parameters)
- Change the value from 0-32 [Rdy] to 96-127 [Exe] to write to the flash
#### Group D
- Read Operations
- Read Program 1-7, 8-15, Read Panel Prms, Init Panel Prms
- Change the value from 0-32 [Rdy] to 96-127 [Exe] to read from the flash
### Circuit Diagram
- This image was created with Fritzing.
- Actually, it is necessary to use Raspberry Pi Pico 2 (instead of Raspberry Pi Pico)
- NOTE: Unlike Digital Synth PRA32-U v3.1.0, the switches are low active and RP2350 uses internal pull-up to avoid RP2350-E9 Erratum
### An Example of Construction Using a Universal PCB
- Using a universal PCB, GY-PCM5102 (PCM5102A I2S DAC Module), 6 SWs, 3 VRs, a OLED Display, and a M5Stack MIDI Unit (optional)
- An connection between Raspberry Pico 2's Mute Off Pin and GY-PCM5102's XSMT is omitted
### An Example of Construction Using a Breadboard
- Using a breadboard, GY-PCM5102 (PCM5102A I2S DAC Module), 3 SWs, 3 VRs, and a OLED Display
- An connection between Raspberry Pico 2's Mute Off Pin and GY-PCM5102's XSMT is omitted
### Table of GUI Pages
| Page | Parameter A | Parameter B |
| :------------- | :------------------ | :--------------- |
| A-00 Info | PRA32-U2/P | v2.5.2 |
| A-01 Voice | Voice Mode | Voice Asgn Mode |
| A-02 Pitch | Portamento | Pitch Bend Range |
| A-03 Osc a | Osc 1 Wave | Mixer Noise/Sub |
| A-04 Osc b | Osc 1 Shape | Osc 1 Morph |
| A-05 Osc c | Osc 2 Wave | Mixer Osc Mix |
| A-06 Osc d | Osc 2 Coarse | Osc 2 Pitch |
| A-07 Osc e | Osc Drift | Osc Saw W Mode |
| A-08 Filter a | Filter Cutoff | Filter Resonance |
| A-09 Filter b | Filter EG Amt | Filter Key Track |
| A-10 Filter c | Filter Mode | |
| A-11 EG a | EG Attack | EG Decay |
| A-12 EG b | EG Sustain | EG Release |
| A-13 EG c | EG Amp Mod | Release = Decay |
| A-14 EG d | EG Mod Amt | EG Mod Dst |
| A-15 EG e | EG Filter Amt | EG Velo Sens |
| A-16 Amp a | Amp Attack | Amp Decay |
| A-17 Amp b | Amp Sustain | Amp Release |
| A-18 Amp c | Amp Gain | Amp Velo Sens |
| A-19 Panner | Pan | |
| A-20 LFO a | LFO Wave | LFO Fade Time |
| A-21 LFO b | LFO Rate | LFO Depth |
| A-22 LFO c | LFO Mod Amt | LFO Mod Dst |
| A-23 LFO d | LFO Filter Amt | |
| A-24 Breath | Breath Filter Amt | Breath Amp Mod |
| A-25 Aft Touch | Aft Touch LFO Amt | |
| A-26 Chorus a | Chorus Level | |
| A-27 Chorus b | Chorus Rate | Chorus Depth |
| A-28 Delay a | Delay Level | Delay Mode |
| A-29 Delay b | Delay Time | Delay Feedback |
| B-00 Panel a | Panel Play Mode | Panel MIDI Ch |
| B-01 Panel b | Panel Play Pitch | Panel Play Velo |
| B-02 Panel c | Panel Scale | Panel Pitch Ofst |
| B-03 Panel d | Panel Transpose | |
| B-04 Seq a | Seq Step Note | Seq Clock Src |
| B-05 Seq b | Seq Transpose | Seq T/Rx St/Sp |
| B-06 Seq c | Seq Tempo | Seq Gate Time |
| B-07 Seq d | Seq Mode | Seq Num Steps |
| B-08 Seq e | Seq On Steps | Seq Act Steps |
| B-09 Seq f | Seq Rand Pitch | Seq Rand Velo |
| B-10 Seq 0 | Seq Pitch 0 | Seq Velo 0 |
| B-11 Seq 1 | Seq Pitch 1 | Seq Velo 1 |
| B-12 Seq 2 | Seq Pitch 2 | Seq Velo 2 |
| B-13 Seq 3 | Seq Pitch 3 | Seq Velo 3 |
| B-14 Seq 4 | Seq Pitch 4 | Seq Velo 4 |
| B-15 Seq 5 | Seq Pitch 5 | Seq Velo 5 |
| B-16 Seq 6 | Seq Pitch 6 | Seq Velo 6 |
| B-17 Seq 7 | Seq Pitch 7 | Seq Velo 7 |
| B-18 Control a | Modulation | Expression |
| B-19 Control b | Breath Controller | Sustain Pedal |
| B-20 Control c | Panic | |
| C-00 Write 0 | Write Program 0 | Write Program 1 |
| C-01 Write 2 | Write Program 2 | Write Program 3 |
| C-02 Write 4 | Write Program 4 | Write Program 5 |
| C-03 Write 6 | Write Program 6 | Write Program 7 |
| C-04 Write a | Write Panel Prms | |
| D-00 Read 0 | Read Program 0 | Read Program 1 |
| D-01 Read 2 | Read Program 2 | Read Program 3 |
| D-02 Read 4 | Read Program 4 | Read Program 5 |
| D-03 Read 6 | Read Program 6 | Read Program 7 |
| D-04 Read 8 | Read Program 8 | Read Program 9 |
| D-05 Read 10 | Read Program 10 | Read Program 11 |
| D-06 Read 12 | Read Program 12 | Read Program 13 |
| D-07 Read 14 | Read Program 14 | Read Program 15 |
| D-08 Read a | Read Panel Prms | Init Panel Prms |