Project Specification
Project Overview
Status: Review — concept approval required. Standalone ESP32 Voice Recorder captures and plays local voice messages; it is not a telephone answering machine. This phase produces documents and a concept sketch only, not schematic, PCB, or enclosure CAD.
Intended Use
First-prototype defaults: indoor desktop use, hobbyist-built compact device, local operation without network services. User records a message, selects saved messages, and listens through the built-in speaker.
What the Device Should Do
- Confirmed: standalone recording and playback using ESP32, microphone, amplifier, speaker and removable microSD storage.
- Proposed interaction: Record toggles recording/stop; Play toggles playback/stop. No simultaneous recording and playback.
- Encoder rotation selects saved messages while idle and adjusts volume while playing. Encoder press has no assigned function and must not introduce another required control.
- Preserve completed recordings across power cycles; stopping recording safely finalizes and closes the file. Unexpected power removal can lose the active recording or damage filesystem metadata; resilience strategy remains to be designed.
Main Features
Confirmed: exactly two buttons, one rotary encoder, microphone, amplifier, speaker, microSD and USB-C power; no battery. Prototype defaults: no display, no network services, mono speech WAV files. Feedback method for no-display selection, recording state, card/full/error conditions remains unresolved; do not silently add controls or indicators.
Mechanical System Architecture
Proposed compact 3D-printed enclosure with separable top and base, internal PCB mockup, speaker behind a top grille, microphone aligned to its own aperture away from speaker, and top controls. USB-C rear; microSD side-accessible.
Top shell: speaker grille | separate mic aperture | Record + Play + encoder
↓ acoustic/control alignment
Internal assembly: speaker + microphone + PCB (concept mockup)
↓ supported by
Base shell; rear USB-C opening; side microSD opening
No numeric enclosure dimensions, PCB envelope, hole positions or component heights approved yet.
Electrical System Architecture
Direction, not a selected BOM: ESP32-S3, digital audio microphone and digital-input class-D amplifier. Exact parts, interfaces and ratings await library/datasheet research in the electronics phase.
Microphone → digital audio → ESP32-S3 ↔ removable microSD
Two buttons + one encoder → ESP32-S3 → digital audio → class-D amplifier → speaker
USB-C → protection/source detection/current control → power conversion → electronic loads
Hardware Subsystems
- Compute: ESP32 required; ESP32-S3 proposed. Local capture/playback and filesystem management.
- Audio input: digital microphone direction; aperture and speaker separation to reduce acoustic coupling.
- Audio output: digital-input class-D amplifier and mono speaker; output power and impedance unselected.
- Storage: removable microSD; insertion/removal behavior and supported cards to be specified.
- UI: two buttons and encoder only; debouncing and state-dependent rotation.
- Power: USB-C only, no battery and no charging circuitry; protection and compliant source-current handling unresolved.
- Debug: programming/debug and boot/reset access to be resolved internally without adding user controls.
Interfaces and Connections
Rear USB-C for power (data use not promised); side microSD access; top Record and Play buttons, encoder, speaker grille and separate microphone aperture. Internal digital audio and storage bus assignments deferred; no pinouts selected.
Power and Runtime Expectations
Powered while a suitable USB source is attached. No battery runtime target, PD or charging. USB source compatibility, available current and peak audio/recording demands must be verified before component selection.
Power Tree and Power Budget
Concept only: USB-C input → protection/source detection/current limiting → regulator(s) and rail distribution → ESP32, microphone, microSD and amplifier. Rail voltages, per-rail currents, regulator efficiency, idle/record/play peaks and thermal budget are not validated; no numerical budget is claimed. No PD planned. Source detection and actual current limiting remain electronics-phase work.
Manufacturing and Assembly Expectations
First prototype: 3D-printed enclosure and custom PCB after approval. PCB layers, assembly vendor, test points, prints, fasteners and material grade are not selected. Parts availability must be checked before committing footprints. ESP32 is a fixed platform requirement; exact MPN substitutions not yet constrained.
Firmware-Relevant Hardware Requirements
Use explicit idle/record/play states and disallow simultaneous record/play. Safely stop, finalize and close WAV recordings; enumerate retained messages after restart. Define sample format/rate, message ordering, encoder bounds, card removal and filesystem error recovery. Define no-display status feedback and programming/update access before electronics freeze. Sudden power loss cannot be advertised as lossless.
Physical Design Expectations
Compact desktop form, comfortable top access, rear power cable, accessible side card. Separate microphone acoustic inlet from speaker grille. Preserve space for ESP32 RF clearance even with networking disabled until module choice is known. Dimensions and tolerances deferred to accepted concept and sourced parts.
Important Design Decisions
Local, standalone product avoids telephone/network dependencies. USB-only power removes battery and charger complexity. No display simplifies the first prototype but requires an explicit feedback/selection scheme. Digital audio direction is provisional, not a validated circuit.
Assumptions
Indoor desktop use, compact 3D printing, no display/network, mono WAV and the interaction mapping are chosen prototype defaults, not additional confirmed user mandates. Visual proportions are concept proposals only.
Change Notes
2026-10-10: Initial specification from confirmed requirements and lead-approved prototype defaults. Empty schematic/layout inspected: zero components/nets and no PCB geometry. Stop at concept approval; electronics, CAD and PCB implementation deferred.