Ping Pong - Distributed Erlang on ESP32

A distributed Erlang application running on ESP32 microcontrollers using AtomVM. Two ESP32 boards communicate over WiFi and play ping-pong by exchanging messages and flashing LEDs.

Prerequisites

AtomVM Image (CRITICAL)

You MUST flash your ESP32 with an AtomVM image built from the main branch, not a release version. The distributed Erlang features required for this project are only available in the latest development version.

To build and flash AtomVM:

git clone https://github.com/atomvm/AtomVM.git
cd AtomVM
git checkout main
# Follow AtomVM build instructions for ESP32
# Flash the generated .img file to your ESP32

Configuration

Edit src/config.erl to set your WiFi credentials:

get() ->
  #{
    sta => [{ssid, "YourSSID"}, {psk, "YourPassword"}],
    port => 6969,
    led => #{pin => 2, flash_duration => 100}
   }.

Build

make build

This compiles the Erlang code and creates an .avm package file at: _build/default/lib/iot_node.avm

Flash

Flash both ESP32 boards with the compiled application:

# Flash both ESP32 at once
make flash

# Or flash individually
make flash1  # Flash ESP32 #1 on /dev/tty.usbserial-0001
make flash2  # Flash ESP32 #2 on /dev/tty.usbserial-3

Note: Update the PORT1 and PORT2 variables in Makefile to match your USB serial ports.

How It Works

1. Both ESP32 boards boot and connect to WiFi
2. Each board starts distributed Erlang with a unique node name based on its IP:
   • atomvm@192.168.1.49
   • atomvm@192.168.1.50
3. After a 5-second stabilization period, the .50 node sends the first ping
4. The nodes exchange ping/pong messages indefinitely
5. Each message reception triggers an LED flash

Network Requirements

• Both ESP32 must be on the same WiFi network
• The application expects IP addresses:
  • 192.168.1.49 for one board
  • 192.168.1.50 for the other
• If your DHCP assigns different IPs, update the logic in src/iot_node.erl:65-68

Troubleshooting

"invalid_challenge" or connection errors

• Ensure both ESP32 are running the same code version
• Check that both boards have the same cookie (AtomVM)
• Verify network connectivity between the boards

Application terminates immediately

• Make sure you're using AtomVM from main branch, not a release
• Check that WiFi credentials are correct in config.erl

Manual Testing

You can also trigger the ping-pong from an Erlang shell:

% Connect to the node
erlang:set_cookie('atomvm@192.168.1.50', 'AtomVM').

% Send initial ping
{ping_pong, 'atomvm@192.168.1.50'} ! ping.

% To stop
{ping_pong, 'atomvm@192.168.1.50'} ! stop.