🚨 Wireless E-Stop

A reliable wireless emergency stop system using nRF24L01+ modules and Arduino-compatible microcontrollers, developed by the Inria Paris Robotics Lab.
This system is designed for robots, machines, or any setup that needs a secure and fast wireless emergency stop.

Project Overview

This project implements a wireless safety system with the following key features: Secure wireless link using nRF24L01+ Configurable RF channel to avoid interferences "Leaky bucket" timeout algorithm to detect signal loss Compact payload for fast transmission

Hardware Requirements

• 2x Arduino-compatible microcontrollers (e.g., Nano, Uno)
• 2x nRF24L01+ RF modules
• 1x Relay module (3.3V or 5V just make sure the relay voltage matches your microcontroller logic level)
• 1x Emergency stop button
• 1x Reset button (for receiver)
• 10x M3 screws (for case assembly)
• 3D printed cases

Pin Connections

Arduino Pin	Transmitter	Receiver
VCC	3.3V nRF24L01	3.3V nRF24L01 and Relay Module
GND	GND nRF24L01, E-stop Button	GND nRF24L01, Relay Module, Reset Button
D2	E-stop Button	Reset Button
D5	——————————————	Relay IN Pin
D9	nRF24L01 CE	nRF24L01 CE
D10	nRF24L01 CSN	nRF24L01 CSN
D11	nRF24L01 SPI (MOSI)	nRF24L01 SPI (MOSI)
D12	nRF24L01 SPI (MISO)	nRF24L01 SPI (MISO)
D13	nRF24L01 SPI (SCK)	nRF24L01 SPI (SCK)

Software Overview

Transmitter (transmitter.ino)

• Reads the state of the emergency stop button
• Sends a boolean message over RF every 100ms
• Allows RF channel configuration at boot by holding the button and using the Serial Monitor

Receiver (receiver.ino)

• Listens for messages from the transmitter
• Uses a "leaky bucket" algorithm to detect communication loss
• Activates the relay (opens the circuit) if:
  • A message is received with true, or
  • No messages received for a set period
• Requires a 3-second button press to rearm system

RF Channel Configuration

Both transmitter and receiver support on-boot channel setup:

1. Hold the button during power-up (E-stop button for transmitter, Reset button for receiver)
2. Open the Serial Monitor at 115200 baud
3. Enter a new channel (0–125)
4. Release the button to finish setup

Tip: Use a high channel number (>100) to avoid interference with WiFi.

Dependencies

Install via Arduino Library Manager:

• RF24
• EEPROM and SPI (built-in)

Hardware Files

CAD and electronic schematics are located in the hardware/ folder.

Contents may include:

• Electronic schematics
• 3D printable case FreeCAD files and STL exports