# Etherbulb open firmware turns ESP32-C3 smart bulb into RF spectrum visualizer

> **Key takeaway:** Etherbulb is GPL-3.0-or-later firmware that repurposes an ESP32-C3 smart bulb as a receive-only 2.4 GHz RF monitor, displaying signal types through color-coded light output with no cloud dependency.

**Published:** 2026-10-19T21:03:00+00:00 
**Source:** Adafruit Electronics 
**Category:** open-hardware 
**Canonical URL:** https://fosswire.org/news/etherbulb-open-firmware-turns-esp32-c3-smart-bulb-into-rf-sp.html 

## Summary
Peter Holzhauser released Etherbulb on GitHub, open-source firmware for ESP32-C3 smart bulbs that visualizes nearby radio frequency activity. The bulb glows blue for Bluetooth, green for Wi-Fi, and a user-selected color for other signals, with brightness indicating signal strength. It requires no app, cloud service, or account, and does not decode content or transmit. The firmware includes a local JSON API and web dashboard for status, configuration, logs, and raw spectrum snapshots.

## How Etherbulb works
- **Hardware target**: Inexpensive ESP32-C3 based smart bulbs
- **RF coverage**: 2.4 GHz band plus adjacent mobile bands, receive-only
- **Signal classification**: Bluetooth (blue), Wi-Fi (green), user-configurable color for other signal types
- **Brightness mapping**: Stronger signals produce brighter light output
- **Safety mechanism**: Hardware-enforced PWM duty cycle check prevents simultaneous RGB and white channel operation
- **Receiver path**: Derived from ESPARGOS project's esp-sdr by Florian Euchner, Zoltan Doczi and contributors
- **Band tables**: Sourced from ESPsoup app
- **Build requirements**: Specific ESP-IDF commit, Python 3.12
- **Local interfaces**: Self-hosted JSON API and dashboard with endpoints for status, configuration, log, and raw RF snapshot

## Why it matters
Etherbulb demonstrates a practical open-hardware approach to RF awareness using commodity IoT hardware, eliminating cloud dependencies typical of consumer smart bulbs. Its reuse of ESPARGOS and ESPsoup components shows growing tooling maturity for ESP32-based software-defined radio applications.