CrowdClock

Self-synchronising LED badges using ESP-NOW

A distributed system where devices don’t sync animations — they sync time.

See the badges in action: 👉 [https://youtu.be/YINVdLlnf9U(https://youtu.be/YINVdLlnf9U)

Badges automatically synchronise their lighting effects when they come close together.

• No pairing
• No configuration
• No central controller

They just… sync.

Each badge broadcasts its local clock using ESP-NOW. Instead of sending raw time, the value is quantised into 50 ms steps:

tick = millis() - (millis() % 50);

When a badge receives a time value greater than its own, it adopts it:

time = max(time_seen);

This creates a simple, emergent synchronisation mechanism:

• No master node
• No topology
• No device tracking

All badges run the same code and derive their behaviour from time:

tick → effect index → effect state → LED output

• Effect selection is based on time
• Effect state is based on time

Once clocks align, everything else follows automatically.

Rounding time to 50 ms:

• Absorbs network latency
• Prevents oscillation
• Ensures stable convergence

• ESP-NOW transmission every ~5 ms
• Multiple opportunities for propagation

Effects are:

• Flashes
• Chases
• Discrete patterns

This avoids visible artefacts from small timing differences.

Each badge includes:

• ESP32-C3 Mini
• WS2812 LED ring
• 1Ah LiPo battery
• Boost/BMS module (5V output)

PCBs were CNC routed and assembled in workshops.

Early versions used socketed ESP32 modules. This caused unreliable ESP-NOW reception.

Removing the sockets and soldering the modules directly resolved the issue.

At 2.4 GHz, small physical details matter.

This project was developed with participants at Inclusive Bytes

• Community workshops
• Soldering and assembly
• Custom lighting effects written by students

The system itself mirrors the process:

many independent parts working together to create something unified.

The badges were created for the Oldham Illuminate Festival.

• Small groups synchronise
• Groups merge and re-align
• The crowd becomes part of the system

• Visualising time propagation
• Multiple competing “time groups”
• Alternative effect systems
• Binary packet format (non-JSON)

https://github.com/Inclusive-Bytes/CrowdClock

/src            → firmware  
/include 		→ header files
/hardware       → PCB and design files  

This project is released under a Creative Commons licence CC BY-NC 4.0

You are free to:

• Share
• Adapt
• Build upon

Please provide appropriate credit.

Synchronise time, not state.

Thanks to everyone at Inclusive Bytes who helped build, test, and extend the badges.