AtomVM Elixir Firmware Example: Wi-Fi SNTP Clock for ESP32

A minimal AtomVM project that:

• Provisions Wi-Fi credentials via environment variables
• Saves them to NVS (non-volatile storage)
• Connects to Wi-Fi and syncs time via SNTP
• Logs local time to the console once per second

Requirements

For the most up-to-date ESP32 hardware and software requirements, refer to the official AtomVM Getting Started Guide.

Hardware

• An ESP32 development board supported by AtomVM (e.g. ESP32-DevKitC, Seeed XIAO-ESP32S3)

Software

• Erlang/OTP 27
• Elixir 1.17.x
• AtomVM toolchain (via exatomvm)
• A serial monitor tool such as:
  • picocom
  • screen
  • minicom

Network

• A 2.4 GHz Wi-Fi network
• Internet access (required for SNTP time synchronization)

Quickstart

# Clone the example AtomVM project with Wi-Fi + SNTP support
git clone https://github.com/mnishiguchi/hello_atomvm_wifi_sta.git

# Enter the project directory
cd hello_atomvm_wifi_sta

# Fetch Elixir dependencies
mix deps.get

# Flash the AtomVM runtime to your ESP32 (one-time setup)
mix atomvm.esp32.install

# Set your Wi-Fi credentials as environment variables
export ATOMVM_WIFI_SSID="your-ssid"
export ATOMVM_WIFI_PASSPHRASE="your-passphrase"

# Build and flash the application firmware to the device
mix atomvm.esp32.flash --port /dev/ttyACM0

# Open a serial monitor to view runtime logs
picocom /dev/ttyACM0

Adjust the serial port if needed (for example /dev/ttyUSB0).

Fetch dependencies

From the project root:

mix deps.get

Install AtomVM (one-time)

Flash the AtomVM runtime to your ESP32:

mix atomvm.esp32.install

Set Wi-Fi credentials (build-time provisioning)

Export your Wi-Fi credentials as environment variables before building/flashing:

export ATOMVM_WIFI_SSID="your-ssid"
export ATOMVM_WIFI_PASSPHRASE="your-passphrase"

Optional:

# If set (any non-empty value), overwrite NVS credentials on every boot
export ATOMVM_WIFI_FORCE=true

Build and flash the application

mix clean
mix atomvm.esp32.flash --port /dev/ttyACM0

During the first boot, the firmware will:

• Store Wi-Fi credentials in NVS
• Connect to the access point (STA mode)
• Synchronize time via SNTP
• Start logging local time once per second

Monitor logs

Open a serial console:

picocom /dev/ttyACM0

You should see logs like:

wifi: first-time provision (stored Wi-Fi credentials in NVS)
wifi: started
wifi: connected to AP
wifi: got IP {192,168,1,123}
sntp: synced {tv_sec, tv_usec}
time: 2026-01-23 21:42:01 (JST)

Firmware provisioning options

Wi-Fi credentials can be provisioned at build time using environment variables. On boot, they are stored in ESP32 NVS and reused on subsequent boots.

Environment variables

Environment variable	NVS key	Description
ATOMVM_WIFI_SSID	wifi_ssid	Wi-Fi SSID to store in NVS
ATOMVM_WIFI_PASSPHRASE	wifi_passphrase	Wi-Fi passphrase (optional for open networks)
ATOMVM_WIFI_FORCE	—	If set, forces credentials overwrite at boot

Provisioning behavior

• First boot (NVS empty)

  • If ATOMVM_WIFI_SSID is set, credentials are written to NVS.

• Subsequent boots

  • Stored NVS credentials are reused.

• Forced provisioning (ATOMVM_WIFI_FORCE set)

  • NVS credentials are overwritten on every boot.
  • If no passphrase is provided, any existing passphrase is removed (open network).

This allows you to:

• Flash once and reboot freely without re-exporting credentials
• Re-provision Wi-Fi by flashing again with ATOMVM_WIFI_FORCE=true