Audio Looper Schematic Design
Worked for 9 mins 57 sec
Done.
Changes made:
- Replaced the five tall PTV09A pots with short Bourns 3386P vertical 10 kΩ trimmers:
- RV1, VR1, VR2, VR3, VR4
- Reconnected each trimmer correctly:
- Pin 1 → GND
- Pin 2 → Teensy ADC signal
- Pin 3 → 3V3
- Placed the trimmers in a lower control row with more clearance from ENC1.
- Rotated/repositioned J2/J3 so their socket openings face outward through the left board edge, with the jack bodies inside the board.
Verification:
- Trimmer schematic nets are restored correctly.
- Focused checks for J2, J3, and the trimmers show no matching open issues.
Routing around the moved/replaced parts will need cleanup before the next full PCB validation.
The audio jacks are STILL the wrong way round. The Teensy is also the wrong way round. The Teensy USB port should be at the edge of the board.
Worked for 10 sec
I’ll correct the physical edge orientation now: flip the audio jacks to the opposite direction and move/rotate the Teensy so its USB connector sits at a board edge, then run focused checks.
Worked for 13 mins 2 sec
Updated the placement again:
- J2/J3 audio jacks were moved to the right board edge and flipped from the previous orientation so the openings should now face outward from the board.
- U1 Teensy 4.1 was moved/rotated so its USB port is at the top board edge for cable access.
- Focused checks for J2, J3, and U1 show no open review issues tied to those parts.
Because J2/J3 and U1 moved, the existing routing in those areas is now stale and will need cleanup/rerouting before final validation.
Clean up routing
Verify jack orientation
Run full review
Check manufacturability
Explain stale routing
Refine this doc
Ask about this doc
Project Specification
Project Overview
Status: Draft schematic design. Compact POKI-inspired 4-track audio looper based on Teensy 4.1 and PJRC Teensy Audio Shield Rev D/D2.
Intended Use
Small desktop instrument/prototype for firmware-controlled mono 4-track looping v1, while retaining stereo hardware line input/output for future stereo looping.
What the Device Should Do
- Capture stereo line input through SGTL5000 codec.
- Store loops on microSD via the Audio Shield.
- Provide 4 track level controls, track buttons, global buttons, encoder, and LED feedback.
- Run from Teensy USB 5 V during prototype use.
Main Features
- Teensy 4.1 MCU.
- Teensy Audio Shield Rev D/D2 with SGTL5000 codec and microSD.
- Stereo panel-mount 3.5 mm TRS line input and line output.
- 4 track level pots plus optional master pot.
- 17 push buttons total plus rotary encoder with push switch.
- 11 status LEDs.
- GPIO expansion/LED shift-register support where needed.
System Architecture
Diagram
Hardware Subsystems
- Core compute/audio: Teensy 4.1 and PJRC Audio Shield using I2S, I2C, and SPI interconnects.
- Controls: analog pots to Teensy ADC pins; buttons via I2C GPIO expander; encoder direct to Teensy GPIO.
- Indication: LEDs driven through 74HC595 serial-in/parallel-out shift registers and current limiting resistors.
- Power: USB 5 V input through Teensy; 3.3 V distributed to logic/control circuitry; local and bulk decoupling.
- Audio I/O: shield line-in/line-out routed to TRS panel jacks; codec headphone VGND is not system ground.
Interfaces and Connections
- I2S: MCLK, BCLK, LRCLK, DIN, DOUT between Teensy and Audio Shield.
- I2C: SDA/SCL shared by SGTL5000 and MCP23017.
- SPI: CS, MOSI, MISO, SCK for microSD on Audio Shield.
- Off-board: line-in jack, line-out jack, pots, buttons, LEDs, encoder.
Power and Runtime Expectations
Prototype powered from USB via Teensy 5 V. No battery runtime target specified.
Power Tree and Power Budget
Table
| Rail | Loads | Estimated Current |
|---|---|---|
| 5 V USB | Teensy VIN and onboard regulation | TBD from module datasheets |
| 3.3 V | Teensy logic, Audio Shield, MCP23017, 74HC595, pots, LEDs | TBD; design target below Teensy 3.3 V regulator capability unless external 3.3 V is added |
Manufacturing and Assembly Expectations
Prototype schematic. Default to SMD passives for compact board unless hand-soldering is requested later. Use clearly labeled connectors for off-board panel wiring.
Firmware-Relevant Hardware Requirements
Firmware must initialize SGTL5000 over I2C, configure I2S audio streaming, access microSD over SPI, scan MCP23017 buttons, read ADC pots, read encoder, and update LED shift registers.
Physical Design Expectations
Keep audio jack-to-codec routes short and separated from LED/button wiring. Use one common ground; do not tie headphone VGND to system ground.
Important Design Decisions
- Use MCP23017 for buttons to save Teensy GPIO.
- Use two 74HC595 devices for 11 LEDs to save GPIO.
- Keep stereo audio hardware for future expansion.
Assumptions
- Teensy 4.1 and Audio Shield are represented as module/header parts if exact Flux library parts are available; otherwise equivalent connectors will be used.
- Prototype power is USB only, with optional future DC jack header/protection placeholder.
Change Notes
- Initial specification derived from attached Looper Schematic Design document.
Project Overview
Intended Use
What the Device Should Do
Main Features
System Architecture
Hardware Subsystems
Interfaces and Connections
Power and Runtime Expectations
Power Tree and Power Budget
Manufacturing and Assembly Expectations
Firmware-Relevant Hardware Requirements
Physical Design Expectations
Important Design Decisions
Assumptions
Change Notes
