IN-9 Spectrum Analyzer

🚧 Early WIP — currently on hold. The hardware design, BOM and project scaffold are here; the firmware is not implemented yet (firmware/src/main.cpp is a stub). Sharing the concept now — active development is paused.

An 8-channel audio spectrum analyzer built on IN-9 neon bargraph tubes, driven by an ESP32-S3 — vintage glow meters dancing to live audio.

Concept

• 7-band spectrum analysis (MSGEQ7) shown across 8 × IN-9 bargraph tubes
• Live, audio-reactive bar levels
• Environmental readout: CO₂ / temperature / humidity (SCD41)
• Real-time clock (DS3231) with NTP sync over WiFi
• Browser-based configuration / web UI

Hardware

Part	Role
ESP32-S3-DevKitC-1 (WROOM-1-N16R8)	MCU + WiFi
IN-9 × 8	neon bargraph display tubes
MSGEQ7	7-band audio spectrum IC
MCP4728 × 2	I²C DACs (tube drive levels)
MGE340 × 8	high-voltage drive transistors
SCD41	CO₂ / temperature / humidity sensor
DS3231	real-time clock
HV PSU 12 V → ~150 V	MC34063 + IRF840 boost for the IN-9 tubes

Assembly notes: docs/assembly-guide.md.

Status & roadmap

• Project structure, hardware BOM, assembly notes
• Web-flasher scaffold (ESP Web Tools) in web/
• Firmware: MSGEQ7 sampling → tube levels via MCP4728
• SCD41 / DS3231 / NTP integration
• Web UI + WiFi provisioning (credentials via captive portal — never hard-coded)
• Publish the browser web-flasher on GitHub Pages once the firmware is functional

Build (firmware)

cd firmware
pio run

The built binaries are copied into web/ for the ESP Web Tools browser flasher. The live "flash from your browser" page will go online (GitHub Pages) once the firmware actually does something — until then it is intentionally not linked.

License

MIT © 2026 Nikolay Mir