📡 NRF24-Spectrum-Scanner

A dual-radio 2.4 GHz band analyzer — ESP32 + 2× NRF24L01+

See the invisible. Legally.

A receive-only RF diagnostic tool that paints a live picture of everything happening in the 2.4 GHz ISM band around you — WiFi, Bluetooth, Zigbee, microwave ovens, RC links — on an OLED and in your browser.

⚖️ 100% legal. The NRF24 modules are used purely as energy detectors — they never transmit. This is a passive spectrum analyzer, not a jammer.

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✨ Features

🚀 Dual-radio parallel sweep	Radio A covers ch 0–62, Radio B covers ch 63–125 → ~2× sweep speed
🌈 Full 2.4 GHz coverage	All 126 NRF24 channels (2.400–2.525 GHz), ~20 sweeps/sec
📺 OLED live display	Two pages: spectrum bar graph with peak-hold, and peak stats
🌐 Browser web UI	Color-coded chart with band overlays (WiFi / BLE / Zigbee / microwave)
📊 CSV serial logging	Full spectrum dump every 5s for offline analysis
🛡️ Graceful degradation	Unplug one radio? The other half keeps sweeping
🔌 Hot-plug friendly	Radios detected at boot, status shown live

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🏗️ Architecture

graph TD
    A[Radio A - NRF24L01+] -->|VSPI| E[ESP32]
    B[Radio B - NRF24L01+] -->|HSPI| E
    E -->|I2C| O[SSD1306 OLED]
    E -->|WiFi AP| W[Browser Web UI]
    E -->|Serial| C[CSV Log]
    subgraph 2.4 GHz Band
    A
    B
    end

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Each radio walks half the band. The firmware merges both halves into one 126-channel spectrum every cycle, then renders it to the OLED, the web UI, and the serial CSV log.

2.400 GHz                                        2.525 GHz
    |────────── Radio A (VSPI) ──────────|────────── Radio B (HSPI) ──────────|
    ch 0                              ch 62  ch 63                         ch 125

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🧰 Hardware

Component	Qty	Notes
ESP32-WROOM-32 dev board	1	Any variant with the pins below free
NRF24L01+ module	2	Add a 10 µF cap across VCC/GND on each — they're picky about power
SSD1306 OLED 128×64	1	I2C, address 0x3C
10 µF electrolytic capacitor	2	One per radio — not optional
Breadboard + jumpers	~20	Female-to-male fit the NRF24 header

🔌 Wiring (quick reference)

NRF24 Pin	Radio A (VSPI)	Radio B (HSPI)
CE	GPIO 22	GPIO 16
CSN	GPIO 21	GPIO 15
SCK	GPIO 18	GPIO 14
MOSI	GPIO 23	GPIO 13
MISO	GPIO 19	GPIO 12
VCC	3.3V	3.3V
GND	GND	GND

OLED: SDA → GPIO 4 · SCL → GPIO 5 · VCC → 3.3V · GND → GND

⚠️ NRF24 modules run on 3.3V only. Never connect VCC to 5V — it will kill the radio.

📖 Full step-by-step guide with circuit diagrams: docs/wiring.md

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🚀 Quick Start

1. Flash it

pio run -t upload
pio device monitor

Or open the folder in VS Code with the PlatformIO extension and hit Upload.

2. Watch the OLED

Within ~2 seconds you'll see A+ B+ and live spectrum bars.

3. Open the web UI

Connect to the ESP32's WiFi AP and open the dashboard:

📶 SSID	NRF24-Scope
🔑 Password	spectrum24
🌐 URL	http://192.168.4.1

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🌐 Web UI

The browser shows a full-resolution spectrum chart with:

• 🎨 Color-coded bars — green (quiet) → yellow → red (busy)
• 🗺️ Band overlays — semi-transparent markers for known 2.4 GHz bands
• 📈 Live stats — radio health, sweep counter, peak channel + frequency + level
• 🏷️ Legend — all marked bands with colors

Band overlays

Band	NRF24 ch	Color	Typical source
WiFi 1	1–5	🔵 Blue	WiFi channel 1 (2412 MHz)
WiFi 6	4–8	🔵 Blue	WiFi channel 6 (2437 MHz)
WiFi 11	9–13	🔵 Blue	WiFi channel 11 (2462 MHz)
BLE adv	0–2	🟢 Green	BLE advertising (ch 37/38/39)
Zigbee	11–26	🟠 Orange	Zigbee / Thread channels
Microwave	40–70	🔴 Red	Oven leakage (~2.45 GHz)

API endpoints

URL	Purpose
/	Main web UI
/data	JSON — full spectrum + stats
/toggle	Switch OLED page (spectrum ↔ peak stats)

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📺 OLED Pages

Page 1 — Spectrum (default)

A+ B+ #1234
[live bar graph with peak-hold dots]

Page 2 — Peak stats

PEAK STATS
Ch: 6 (2406 MHz)
Level: 87%
Sweeps: 1234
Radio A: OK
Radio B: OK

Toggle via http://192.168.4.1/toggle.

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📊 CSV Logging

The firmware dumps a CSV line every 5 seconds to serial:

CSV,timestamp_ms,ch0,ch1,ch2,...,ch125

Capture it:

pio device monitor > spectrum_log.csv

Then analyze offline — see docs/usage.md for a ready-to-run Python/pandas example.

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🔍 Reading the Spectrum

What you see	What it is
Tall bars at ch 1–5 / 4–8 / 9–13	📶 WiFi channels 1 / 6 / 11
Hopping spikes across ch 0–79	🎧 Bluetooth classic
Persistent spikes at ch 0–2	📳 BLE advertising
Broad hump at ch 40–70	🍿 Microwave oven (when running)
Periodic narrow spikes at ch 11–26	🐝 Zigbee / Thread
Fixed repeating narrow spikes	🎮 RC links, wireless keyboards/mice

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📚 Documentation

• 🔧 docs/wiring.md — step-by-step wiring, circuit diagrams, troubleshooting
• 📖 docs/usage.md — web UI, OLED, CSV logging, signal interpretation, performance notes

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⚙️ Performance

Metric	Value
Sweep rate	~20 full-band sweeps/sec (50 ms/sweep)
Sensitivity	~−64 dBm (NRF24 carrier-detect threshold)
Resolution	1 MHz per channel (126 channels / 126 MHz)
Web UI latency	300 ms refresh
OLED latency	50 ms refresh

This is a poor-man's spectrum analyzer — energy presence only, no demodulation. That's exactly what makes it legal and safe. For protocol-level decoding you'd need an SDR or dedicated sniffer.

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📄 License

MIT — see LICENSE. Built from scratch, yours to use and modify.

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⚖️ Legal

This device is receive-only and does not transmit, interfere with, or disrupt any radio communications. It is a passive diagnostic tool suitable for education, hobby use, and site surveys. Always follow your local regulations regarding radio equipment.