ESP32 Ma Bell Bluetooth Gateway

Ma Bell Project #

Bluetooth Phone Gateway for vintage telephone integration.

Project implemented in a separate repository.

✓ 19 | ↻ 7 | ⏳ 50 (76 total)

Legend: ✅ Complete | 🔄 In Progress | ⏳ Planned

Project Vision & Scope 🔄 #

Restore full, authentic use of vintage analog telephones by bridging them to modern Bluetooth cell phones — preserving rotary dialing, ringing behavior, tones, and user experience.

In Scope

  • Rotary dial pulse detection
  • Authentic ring, dial tone, busy/reorder tones
  • Bluetooth HFP call handling
  • Use of original phone and ringer hardware

Out of Scope

  • VoIP provider integration
  • Multi-line PBX features
  • Smartphone UI replacement
Requirements & Constraints — Complete

Requirements & Constraints ✅ #

Define what success means before building.

  • ✅ User scenarios (incoming/outgoing calls, edge cases)

  • ✅ Functional requirements (FR-xxx)

  • ✅ Non-functional requirements (latency, audio quality, reliability)

  • ✅ Electrical & mechanical constraints

  • ✅ Acceptance criteria for each requirement

  • ✅ Risk register (top technical risks + mitigations)

Architecture & Design — Complete

Architecture & Design ✅ #

Translate requirements into a complete system design.

  • ✅ System block diagram

  • ✅ Power architecture & protection strategy

  • ✅ Audio signal chain & gain staging plan

  • ✅ Hook switch, dial pulse, and ring detection design

  • ✅ Bluetooth integration architecture

  • ✅ Firmware architecture & state machine definition

  • ✅ Interface specifications (electrical, audio, software)

  • ✅ Verification & test plan (requirements → tests mapping)

Low-Voltage Test Rig (EVT-1) 🔄 #

Safe, breadboard-based simulator for firmware development — no line voltage required.

📄 Build guide: impl/low-voltage-test-rig.md

  • 🔄 Order & collect low-voltage components
  • ⏳ Breadboard ESP32 + PCM5100 DAC + PCM1808 ADC
  • ⏳ Hook switch simulator (GPIO 32)
  • ⏳ Pulse dial simulator (NE555 timer)
  • ⏳ Ring indicator & ring detect feedback
  • ⏳ Audio I/O validation (I2S wiring)
  • ⏳ DTMF tone generator for touch-tone dial simulation
  • ⏳ LED & button wiring
  • ⏳ Full 24-feature firmware test matrix pass

Firmware Development 🔄 #

ESP32 firmware implementing telephony behavior and system control.

  • ✅ ESP32 base firmware & build system
  • ✅ Bluetooth HFP profile implementation
  • ✅ Call state machine implementation
  • 🔄 Dial tone, ring, busy, reorder tone generation
  • 🔄 Rotary pulse detection & validation
  • ⏳ DTMF detection (touch-tone phone support)
  • ✅ Configuration storage (NVS schema)
  • ✅ Logging & diagnostics
  • 🔄 Firmware versioning & release tagging
  • ⏳ Validate firmware against low-voltage test rig

Full-Voltage Prototype (EVT-2) ⏳ #

Production-representative prototype with SLIC, ring generator, and real telephone. Using KS0835F SLIC module (AG1171/AG1170 compatible) for the line interface.

📄 Build guide: impl/prototyping-build-guide.md

  • ⏳ Sub-A: ESP32 + codec breadboard (3.3V)
  • ⏳ Sub-B: KS0835F SLIC module + line interface (mixed voltage)
  • ⏳ Sub-C: Ring generator (48V→90V AC)
  • ⏳ Power sequencing & safety validation
  • ⏳ Integration of all sub-assemblies
  • ⏳ Audio path measurements (levels, noise, echo)

Firmware Adjustment (EVT-2 Integration) ⏳ #

Validate and tune firmware on the full-voltage prototype. Should be largely compatible from EVT-1 testing.

  • ⏳ Re-run test matrix against full-voltage hardware
  • ⏳ Tune audio gain staging for SLIC signal path
  • ⏳ Validate ring-trip and hook detection with real phone

Custom PCB (DVT) ⏳ #

Transition from prototype to a reproducible hardware design.

  • ⏳ Schematic capture
  • ⏳ BOM with alternates
  • ⏳ PCB layout & DFM/DFA review
  • ⏳ Test points & programming header
  • ⏳ Fabrication
  • ⏳ Assembly
  • ⏳ Hardware bring-up checklist
  • ⏳ Electrical verification against requirements

Enclosure & Mechanical Integration ⏳ #

Package the device for real-world use.

  • ⏳ Enclosure requirements & constraints
  • ⏳ Connector placement & strain relief
  • ⏳ Enclosure design (3D print or fabrication)
  • ⏳ Thermal and safety considerations
  • ⏳ Final mechanical assembly

Verification & Validation ⏳ #

Prove the system meets its requirements.

  • ⏳ Requirements → test traceability
  • ⏳ Functional test execution
  • ⏳ Audio quality & latency validation
  • ⏳ Long-duration stability testing
  • ⏳ Regression testing after changes
  • ⏳ Issue tracking & resolution

Production Readiness (PVT) ⏳ #

Prepare the design for repeatable builds.

  • ⏳ Assembly documentation
  • ⏳ Manufacturing test procedure
  • ⏳ Test fixtures / jigs
  • ⏳ Calibration & setup process
  • ⏳ Revision control (Rev A, Rev B, etc.)

Documentation 🔄 #

Create durable documentation for users and future builders.

  • 🔄 Build instructions
  • 🔄 Installation & wiring guide
  • 🔄 User guide
  • ⏳ Troubleshooting guide
  • ⏳ Design notes & lessons learned

Deployment & Operations ⏳ #

Put the system into real use.

  • ⏳ Final integration testing
  • ⏳ Installation procedure
  • ⏳ Field diagnostics workflow
  • ⏳ Release notes
  • ⏳ Ongoing maintenance plan
Page last modified: March 26, 2026