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CAI Collision Awareness Indicator (ESP-IDF Prototype)

This repository contains the embedded prototype for the CAI (Collision Awareness Indicator) concept: a pole-mounted traffic safety system that detects near-collision risk and triggers a visual warning. THis project is build on blink example of ESP-IDF, which is a simple template for ESP32 projects. The code is organized in a single main file for simplicity, but can be refactored into multiple files and modules as needed.

What this firmware does (2026-04-19)

Current firmware in main/blink_example_main.c implements a real-time proximity and collision-risk warning loop using a TF-Mini Plus LiDAR over UART.

It:

  • reads TF-Mini frames at 115200 baud on UART2
  • computes approach speed and time-to-collision (TTC)
  • triggers alarm output when danger conditions are met
  • keeps alarm active with a cooldown timer to avoid rapid flicker
  • drives two GPIO outputs (one solid warning output and one blinking warning output)

The logic includes two trigger modes:

  1. Immediate near-proximity mode ("jump scare") when object is <= 50 cm (for up to 3 s in-zone).
  2. TTC mode when estimated time to collision drops below 2.0 s.

Hardware and pin mapping

Defined in main/blink_example_main.c:

  • TF-Mini UART TX pin: GPIO12 (TXD_PIN)
  • TF-Mini UART RX pin: GPIO13 (RXD_PIN)
  • UART port: UART_NUM_2
  • Blinking warning output: GPIO5 (BLINK_PIN)
  • Solid warning output: GPIO6 (SOLID_PIN)

Thresholds and timing:

  • max tracked distance: 600 cm
  • valid sensor range accepted: 1 to 1199 cm
  • TTC danger threshold: < 2.0 s
  • cooldown time: 4.0 s
  • proximity window: <= 50 cm
  • proximity timeout: 3.0 s

Build and flash (ESP-IDF)

You can build and flash the firmware using ESP-IDF tools either visual Studio Code extension or command line.

From the repository root:

idf.py set-target esp32s3
idf.py build
idf.py -p <PORT> flash monitor

Example port on Windows:

idf.py -p COM4 flash monitor

Serial output

The firmware prints periodic distance logs and danger events such as TTC warnings.

Typical messages include:

  • Distance: <n> cm
  • TTC DANGER! Dist: <n> cm, Speed: <n> cm/s
  • Ignoring unrealistic approach speed: <n> cm/s
Distance: 39 cm
Distance: 166 cm
Ignoring unrealistic approach speed: 1129 cm/s
Distance: 53 cm
Distance: 55 cm
Distance: 55 cm
Distance: 56 cm
Distance: 49 cm
TTC DANGER! Dist: 49 cm, Speed: 39 cm/s
Distance: 146 cm
TTC DANGER! Dist: 130 cm, Speed: 156 cm/s
TTC DANGER! Dist: 107 cm, Speed: 224 cm/s
Distance: 105 cm
Distance: 154 cm
Distance: 156 cm
Distance: 155 cm
Distance: 155 cm
Distance: 154 cm
Distance: 152 cm

Optional plotting utility

main/serial_plotter.py provides a live serial distance plot using pyqtgraph and pyserial.

Update the serial port in the script if needed:

  • COM_PORT = 'COM4'

Install dependencies:

pip install pyqtgraph pyserial pyqt5

Run:

python main/serial_plotter.py

Hardware prototype

The current hardware prototype consists of:

  • ESP32-S3-DevKitC-1 development board for the main controller and processing unit
  • TF-Mini Plus LiDAR for distance measurement and collision risk estimation
  • Breadboard and jumper wires for GPIO connections
  • 4s 21700 lion battery pack for portable power
  • usb c step-down power module to convert battery voltage to 5V for the ESP32, relays, 5v LED strip and TF-Mini Plus
  • switch for tuning the system on and off
  • 100w cop led with adjustable step-up driver for the visual warning output
  • two 5v relay modules for controlling the LED warning output
  • 5v Led strip for blinking warning output,(audio output can be added in parallel in the future)

Wiring diagram

protoptype wiring diagram for the TF-Mini Plus LiDAR and GPIO outputs: wiring diagram picture 1, wiring diagram

Functional prototype photos

wiring picture 2, wiring of the prototype Everything is placed inside cardboard box for demo purposes. Carboard is easy to work with and provides a good platform to realize layout of electronics for more robust implementations. Box used is old filament box. esp32 picture 3, ESP32-S3-DevKitC-1 development board Heart of the prototype is the ESP32-S3-DevKitC-1 development board, which provides the processing power and GPIO interfaces for the system. Wiring is build on a breadboard for easy prototyping and testing. Connections are glued with hot glue to secure them in place for field testing. And for easy removal when need to update hardware. cobcutout picture 4, COB LED cutout cob led, heasink, coling fan and step-up are inside cardboard box. Cutout is made for the COB LED.

lidar picture 5, TF-Mini Plus LiDAR TF-Mini Plus LiDAR is mounted on the side of box to provide a clear line of sight for distance measurements. It is connected to the ESP32 via UART for real-time data acquisition. cutout was already in filament box.

switch picture 6, switch for tuning the system on and off, maximun continous current of the switch is 6A, which is 14.4v*6A=86.4W, which is enough for the prototype, since the COB LED is 100W but we will run it at around 60% brightness to stay within the limits of the switch and thermals.

text picture 7, thermal testing.

text picture 8, thermal testing. COB LED temperature at continuous load. surface temperature stabilizes at 126°C, which is too high for long-term reliability. at 60% brightness, for short demo purpose, its fine as it will not be on for long time, but for more robust implementations, better cooling solutions should be considered, such as larger heatsinks, active cooling with fans, or even liquid cooling if necessary.

Next steps

The broader CAI concept targets right-hook conflict prevention at intersections by combining:

  • pole-mounted sensing (RGB + IR in concept)
  • on-device collision prediction
  • immediate crossing illumination warning

This repository currently hosts the embedded warning prototype and ESP-IDF project scaffolding for iterative field testing.
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