ESPHome ITS-G5 Receiver

An ESPHome component that turns an ESP32-C5 into a receiver for ITS-G5 / 802.11p Cooperative Intelligent Transport Systems (C-ITS) messages broadcast by road traffic infrastructure (traffic lights, road side units, ...). It captures the raw frames and hands them to your automations via an on_packet trigger — for example to forward them to OpenTrafficMap.

This project stands entirely on the shoulders of the excellent opentrafficmap / its-g5-receiver-firmware. The opentrafficmap team did the hard part: they figured out how to coax the ESP32-C5's WiFi radio into 802.11p mode at all — using the otherwise undocumented PHY functions phy_11p_set() and phy_change_channel() hidden in Espressif's binary PHY blob. Without their reverse-engineering, discovery, and open publication of that firmware, this ESPHome port simply would not exist.

If you want a ready-made, purpose-built receiver, please look at their project and hardware first. Huge thanks to the opentrafficmap community. See also their wiki and the map.

This repository is just a re-implementation of that firmware's core as a reusable ESPHome component, so it can be combined with the rest of the ESPHome ecosystem (Home Assistant, any uplink, other sensors, ...).

Please do me a favor: 👍 If you use any information or code you find here, please link back to this page. ⭐ Also, please consider to star this project. I really like to keep track of who is using this to do creative things, especially if you are from other parts of the world. 😃 You are welcome to open an issue to report on your successful project and share it with others.

Component configuration

Add the component via external_components and then configure the receiver:

external_components:
  - source: github://hn/esphome-its-g5
    components: [ its_g5_receiver ]

its_g5_receiver:
  id: g5
  channel: 5900          # ITS-G5 channel in MHz (G5CC=5900, G5SC2=5890,
                         # G5SC1=5880, G5SC3=5870, G5SC4=5860)
  broadcast_only: true   # only forward broadcast frames
  on_packet:
    - lambda: |-
        // x       -> std::vector<uint8_t>  (raw frame bytes)
        // rssi    -> float                 (dBm)
        // channel -> int
        // rate    -> int
        ESP_LOGD("main", "got %d bytes, rssi=%.0f", x.size(), rssi);

on_packet trigger

Fired for every captured (and, if broadcast_only, broadcast) frame. Lambda variables:

Variable	Type	Meaning
x	std::vector<uint8_t>	raw frame bytes
rssi	float	receive signal strength (dBm)
channel	int	reception channel
rate	int	reception rate field

Sensors

The sensor platform exposes optional cumulative counters:

sensor:
  - platform: its_g5_receiver
    its_g5_receiver_id: g5
    bytes_received:
      name: "Bytes Received"
    packets_received:
      name: "Packets Received"
    packets_dropped:
      name: "Packets Dropped"

The bytes_received sensor shows the total size of the received frames (the raw frame as captured, without the FCS checksum). The packets_received sensor shows the frames received and dispatched to on_packet, the packets_dropped sensors shows frames dropped in the RX callback because the internal work queue was full or memory was exhausted (a load/back-pressure indicator; should stay 0 in normal operation).

The component intentionally leaves out some features of the reference firmware to stay lightweight: the remote command topic, runtime (NVS) reconfiguration, pcap capture, and the firmware's HW_VARIANT OTA logic (ESPHome has its own OTA).

Using it with OpenTrafficMap

OpenTrafficMap collects C-ITS messages from receivers all over the place and visualises traffic infrastructure on a public map. This repo ships a complete, ready-to-flash example config, its-g5-opentrafficmap.yaml, that receives frames and forwards them to the OpenTrafficMap MQTT server — reproducing the reference firmware's behaviour.

Warning

Using its-g5-opentrafficmap.yaml as a replacement for the original firmware is highly experimental and risky, since the OpenTrafficMap hardware uses the KSZ8851SNL Ethernet chip, which is not (yet) included in the standard ESPHome distribution. A patched Ethernet component is shipped with this project, which adds support for the KSZ8851SNL. This patched component is likely to compile only with ESPHome version 2026.6; expect it to break soon.

Note

If you are using your own hardware without the KSZ8851SNL chip (e.g. a W5500 or a ENC28J60), everything should generally work fine. Don't forget, in this case, to adjust the ethernet: section to match your hardware, and be sure to remove ethernet from the components: list in the external_components: section of the YAML file.

Setup

Every receiver publishes under a node ID, used in all MQTT topics (its/<node_id>/...). You need to set it once as a substitution at the top of the config:

substitutions:
  node_id: "aabbccddeeff"   # Ethernet MAC hex, or a friendly name (e.g. node789)

• Ethernet MAC (default): the reference firmware uses the device's Ethernet MAC as lowercase hex (e.g. aabbccddeeff). Using the same value makes this ESPHome build present the same identity as a device already known to OpenTrafficMap. If you don't know the MAC, flash once and read it from the device log, or from the info topic (field emac).
• Friendly name: OpenTrafficMap can assign your device a friendly name (e.g. node789); if so, put that in node_id.

Publishing to the OpenTrafficMap server is anonymous — no username or password is required. For registering a device, assigning a friendly name, showing it on the map, or getting credentials to subscribe to your own node's messages, see the OpenTrafficMap node registration wiki.

Installation

Use esptool --chip esp32c5 -p /dev/ttyACM0 -b 921600 --before=default-reset --after=hard-reset write-flash 0x0 its-g5-firmware.factory.bin to install the ESPHome factory image on the ESP32 (USB port on the left).