WiFi Spectrum Display

A WiFi spectrum analyzer for ESP32-C3 that visualizes 2.4GHz WiFi activity on a NeoPixel LED strip. Monitor packet traffic or signal strength across all 13 WiFi channels in real-time.

Features

• Two Scan Modes

  • Traffic Mode: Passively monitors packet traffic per channel
  • RSSI Mode: Scans for access points and displays signal strength

• Display Modes

  • Solid color with adjustable hue/saturation
  • Colormaps (Jet, HSV, Autumn, Hot, Cool, Viridis, Plasma, Turbo)
  • Rainbow scroll
  • Cycling color

• Web Configuration UI

  • Connect to the device's WiFi AP to configure settings
  • Real-time preview of changes
  • Captive portal auto-opens settings page

• Persistent Settings

  • All settings saved to flash memory
  • Survives reboots

• Button Controls

  • Short press: Cycle display mode
  • Double press: Toggle WiFi AP for settings
  • Long press (3s): Power on/off

• RGB Button LED

  • White breathing: Normal operation
  • Solid blue: AP mode active
  • Off: Powered down

Hardware

Components

Component	QTY.	Description	Example Online Source
SeeedStudio Xiao ESP32-C3	1	Main microcontroller	https://www.seeedstudio.com/Seeed-XIAO-ESP32C3-p-5431.html
WS2812B Strip	1	144led/m IP30 (i.e. no covering) ~30cm strip, usually sold per meter	https://www.aliexpress.com/item/1005009096063569.html
Momentary Button with RGB LED	1	Common cathode button LED 5v 16mm low profile momentary	https://www.aliexpress.com/item/4001160061412.html
M2.5X16mm screws	5	Countersunk head	https://www.aliexpress.com/item/32946954901.html
M2.5X8mm screws	2	Countersunk head	https://www.aliexpress.com/item/32946954901.html

Some wire for connecting all the parts.

Wiring

Function	GPIO Pin
NeoPixel Data	8
Button	5
Button LED Red	4
Button LED Green	3
Button LED Blue	2

Connect NeoPixel VCC to 5V and GND to GND.

3D Printed Enclosure

Print files are located in the 3D prints folder. The model is already oriented for printing and no supports are necessary. I think 0.15-0.2mm layer height is good. The screws are meant to thread there own holes

Software Setup

Dependencies

Install these libraries via Arduino Library Manager:

• FastLED - NeoPixel control
• WebServer - Built-in with ESP32
• DNSServer - Built-in with ESP32
• Preferences - Built-in with ESP32
• ArduinoOTA - Built-in with ESP32

Installation

1. Install Arduino IDE or PlatformIO
2. Add ESP32 board support (Arduino ESP32 core)
3. Install the FastLED library
4. Open wifi_spectrum_display/wifi_spectrum_display.ino
5. Select your ESP32-C3 board
6. Upload

Usage

First Boot

1. Power on the device
2. The LED strip will show a startup animation
3. The button LED will breathe white

Accessing Settings

1. Double-press the button (LED turns blue)
2. Connect to WiFi network: WiFi-Spectrum
3. Password: spectrum123
4. Settings page should open automatically (if not go to http://192.168.4.1)
5. Configure display mode, colors, brightness, etc.
6. Click "Save & Exit" or double-press button to save and close AP

Settings

Setting	Description
Display Mode	Solid Color, Colormap, Rainbow Scroll, Cycling Color
Scan Mode	RSSI (signal strength) or Traffic (packet count)
Colormap	Choose from 8 scientific colormaps
Solid Color	Hue and saturation for solid color mode
Brightness	NeoPixel strip brightness (0-100%)
Button LED	Button LED brightness (0-100%)
Max Current	Power limiting for LED strip (100-5000mA)

OTA Updates

The device supports over-the-air updates when the AP is active:

• Hostname: wifi-spectrum
• Password: spectrum123

How It Works

Traffic Mode (Default)

The ESP32 enters WiFi promiscuous mode and passively listens for all WiFi packets on each channel. It hops through all 13 channels, counting packets on each. Channels with more traffic appear brighter on the LED strip.

This is completely passive - no packets are transmitted.

RSSI Mode

The ESP32 scans for nearby access points and maps their signal strength to the LED strip based on which channel they're on. Stronger signals appear brighter.

LED Mapping

The LEDs are mapped across 13 WiFi channels using a Gaussian kernel for smooth blending between adjacent channels. Each channel's activity spreads across multiple LEDs with a bell-curve distribution. The design targets 46 LEDs, but this can be adjusted via NUM_LEDS in the code.

Configuration

Key settings in the code (wifi_spectrum_display.ino):

#define NUM_LEDS          46      // Number of NeoPixels
#define CHANNEL_HOP_MS    10      // Time per channel in traffic mode
#define DECAY_FACTOR      0.95f   // LED brightness decay rate
#define LONG_PRESS_MS     3000    // Long press duration

WiFi AP settings:

const char* AP_SSID = "WiFi-Spectrum";
const char* AP_PASS = "spectrum123";

License

MIT License - Feel free to use and modify.