CO2 Dragster Racing Timer System

A 2-lane CO2 dragster race timing system. Each lane has a dedicated Teensy 4.0 MCU measuring elapsed race time with microsecond resolution, reporting results to a central ESP32 master that serves a live web page over WiFi.

System Overview

[Start Button] ──> [1× Relay] ──> CO₂ Solenoids L1 + L2 in parallel (fires both lanes)
               └──> Teensy L1 + Teensy L2 (hardware interrupt, simultaneous start)

[850nm IR Laser]──beam──>[SFH203 + LM393]──> Teensy (interrupt on beam break = finish)

Teensy L1 ──UART──> ESP32 Master ──WiFi──> Web Browser (live results)
Teensy L2 ──UART──> ESP32 Master

Hardware

Component	Qty	Purpose
Teensy 4.0	×2	Lane timer MCU — 600 MHz, hardware interrupts, µs timing
ESP32 dev board	×1	Master MCU — WiFi web server, receives times from both lanes
850 nm IR Laser Module	×2	Finish line emitter
SFH203 Photodiode	×2	Finish line receiver (~5 ns rise time)
LM393 Comparator Module	×2	Converts photodiode signal to clean digital edge
5V Relay Module	×1	One relay fires both CO₂ solenoids wired in parallel
Jaycar SS0903 Solenoid	×2	12V — fires CO₂ launcher over-centre mechanism
Momentary pushbutton	×1	Start trigger — simultaneously starts both timers and fires CO₂

See hardware/BOM.md for the full component list including launcher hardware.

Timing Accuracy

• Resolution: 1 µs (micros() on Teensy 4.0 at 600 MHz)
• Interrupt latency: ~100–200 ns
• Practical accuracy: Limited by beam geometry and car body width (~0.1–0.5 ms), not electronics
• Target spec: 1 ms — exceeded by ~1000×

3D Printed Launcher

Based on Printables model 451928 — over-centre spring mechanism fired by a 12V solenoid. Print two complete sets (one per lane).

Default solenoid: Jaycar SS0903 — use Launcher - centre plate 12mm.stl Alt solenoid: 13X30TL (13mm OD × 30mm) — use Launcher - centre plate 12mm - MOD for 13X30TL Solenoid.stl

STL File	Notes
Launcher - centre plate 12mm.stl	Default — fits Jaycar SS0903
Launcher - centre plate 12mm - MOD for 13X30TL Solenoid.stl	Modified — fits 13X30TL
Launcher - stand.stl
Launcher - hammer.stl	Drives the CO₂ piercing bolt
Launcher - lever.stl	Over-centre arm
Launcher - knob.stl
Launcher - nozzle.stl	CO₂ car guide
Launcher - inner plate 3mm.stl
Launcher - outer plate 12mm.stl
Launcher - outer cover 3mm.stl

Repository Structure

firmware/
  lane_timer/lane_timer.ino   — Teensy 4.0 (identical firmware for both lanes)
  master/master.ino           — ESP32 master with WiFi web UI
hardware/
  BOM.md                      — Full component list (electronics + launcher hardware)
3D Model/
  Launcher/                   — STL files for the CO₂ launcher (print ×2)
docs/
  wiring_guide.md             — Step-by-step wiring instructions and circuits
plan.md                       — System design document

Firmware Setup

Lane Timer (Teensy 4.0)

1. Install Teensyduino
2. Open firmware/lane_timer/lane_timer.ino in Arduino IDE
3. Board: Teensy 4.0, CPU Speed: 600 MHz
4. Upload the same sketch to both Teensys — lane ID is set by a hardware jumper on Pin 4:
   • Lane 1: jumper Pin 4 → 3.3V
   • Lane 2: leave Pin 4 unconnected

Master (ESP32)

1. Install ESP32 Arduino core
2. Install library: ArduinoJson (Benoit Blanchon)
3. Open firmware/master/master.ino
4. Board: ESP32 Dev Module
5. Upload, then connect to WiFi AP CO2_Dragster and browse to http://192.168.4.1

UART Protocol

Communication between each Teensy and the ESP32 uses 115200 baud ASCII lines:

Direction	Message	Meaning
Teensy → ESP32	LANE:x READY	Ready for a race
Teensy → ESP32	LANE:x START	Start interrupt fired
Teensy → ESP32	LANE:x TIME:xxxxxx	Race finished; elapsed time in µs
Teensy → ESP32	LANE:x FAULT:BEAM	Beam not detected at startup
ESP32 → Teensy	RESET	Reset to READY state
ESP32 → Teensy	STATUS	Request current state

Wiring

See docs/wiring_guide.md for full wiring instructions, circuit diagrams, and the pre-race checklist.

License

MIT — see LICENSE