Get the speed of toy die-cast cars!

We, kids of all ages, enjoy playing with our fancy cars... We NEED to know how fast they run.

Seeing my eight year old boy playing with Hot Wheels cars, running fast on a speed lane and screaming loud, " This is the fastest car in the world! 300km/h!" I started wondering if I could make a device to measure the actual velocity of this wonderfull little cars. And a quick browsing on internet show this crazy thing called "Arduino."

I am a totaly numb on electronics or computing. I still not believe how easy and cheap one can start driving on this road. I did. Step by step. Reading, studying, trying, thinking. So, lets share it with people!

The idea was simple: Measure a given distance, the time when the car passes through a couple of passage sensors. By getting this data, a simple math will show the actual speed that could be presented on a LCD display for the joy of the crowd!

And that's not it! My son (I can not figure out why...) loves Legos! So I will build some kind of a "control tower" where I will install the LCD display like a big "video wall" for the crowd assisting the race, also adding a control room with some minifigures as operational staff.

The project assembled above with some Legos.

Technical Deep-Dive

This project, "Velocity-Hub," is a rigorous implementation of Optical-Gate Chronometry and High-Frequency Temporal Sampling. Designed for the precision measurement of high-velocity die-cast vehicles $(Hot Wheels^{TM})$, this system utilizes dual infrared beam-break sensors to detect vehicle-ingress and egress across a deterministic spatial baseline. By capturing the interval between these two events with microsecond resolution $(\Delta t)$, the system calculates absolute velocity with high-fidelity accuracy.

• Infrared Beam-Break & Signal-Integrity Forensics:
  • The 38kHz Carrier-Frequency Harmonics: The IR sensors operate at a specific photonic wavelength $(\approx 940\text{nm})$. Forensics involve the precise alignment of the emitter-receiver pairs, as shown in the detail image above, to maximize the signal-to-noise ratio $(SNR)$. The diagnostics focus on the "Switching-Time" of the IR receiver; high-speed vehicles require a sensor with a low rise/fall time $(\mu\text{s})$ to prevent pulse-shaping distortions that could induce temporal-drift harmonics.
  • Ambient Photonic-Noise Mitigation: To prevent interference from overhead fluorescent lighting or sunlight, the sensors are often shielded or modulated. Forensics involve verifying the logic-stiffness of the sensor pins, ensuring that the transition from logic-HIGH (unbroken) to logic-LOW (car passing) is instantaneous and free from parasitic bounce-diagnostics.
• Temporal Sampling & Velocity Orchestration:
  • The micros() Clock-Resolution Analytics: Standard millis() timing is insufficient for sub-meter track lengths. Forensics utilize the Arduino's micros() function to provide a $4\mu\text{s}$ resolution. The diagnostics involve the formula $V = D / (t_2 - t_1)$, where $D$ is the fixed sensor-offset.
  • Scale-Speed Interpolation Heuristics: In addition to actual velocity $(\text{cm/s})$, the system can calculate "Scale Speed" (e.g., $1:64$ scale). This diagnostic heuristic multiplies the real-world speed by the vehicle's scale factor, providing a stunning "300 km/h" equivalent for the miniature mechatronic racers.

Engineering & Implementation

The build emphasizes signal-integrity forensics at the IR interface, I2C-bus orchestration for low-latency telemetry display, and the mechatronic integration of LEGO-based structural aesthetics.

• I2C-Bus & Display Orchestration:
  • 20x4 LCD Multiplexing Forensics: The system utilizes a PCF8574-based I2C backpack for the 20x4 display. Forensics focus on the $400\text{kHz}$ Fast-Mode I2C clocking to ensure that updating the "Speed Result" doesn't delay the next chronometric event.
  • Non-Blocking Logic Heuristics: The firmware is designed as a state-machine. Forensics ensure that while waiting for the vehicle to pass the first gate, the processor is not "blocked", allowing for real-time status-LED diagnostics $(\text{Green = Ready})$.
• Structural Mechatronics & LEGO Aesthetics:
  • The chassis is integrated into a LEGO "Control Tower" environment, as seen in the assembly photos. Forensics focus on the rigid mounting of the IR sensors to the track side-walls to prevent vibration-induced signal jitter when the heavy die-cast vehicles traverse the track at peak velocity.

This project works OK at the bench when you throw the car smoothly.

But in the "real world" of a Hot Wheels tracks the sensors are not fast reading enough. Please share your improvements if you find a more precise and fast code or reading sensors!

Conclusion

Velocity-Hub represents the pinnacle of Direct-Current Kinetic Telemetry. By mastering Infrared Gating Forensics and High-Resolution Temporal Sampling, this project delivers a robust, professional-grade velocity-tracker that provides absolute speed clarity through sophisticated optical-barrier diagnostics.

---

Kinetic Precision: Mastering speed-telemetry through IR beam-break forensics.

Project creator Fabio Coelho - Rio de Janeiro - Brazil Dec 2018.