DIY Reaction Timer – Arduino MAX7219 Reflex Meter

# DIY Reaction Timer ⚡⏱
Measure your reflexes in milliseconds!  
This pocket‑sized device pairs an **Arduino Uno**, a **MAX7219 8 × 8 LED matrix**, and a single push‑button inside a snap‑fit, screw‑free case.

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## How It Works
1. Press the button to arm the timer.  
2. A random pixel lights up on the LED matrix.  
3. Hit the button as fast as you can.  
4. Your reaction time (and a cheeky emoji rating) scrolls across the display.

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## Print Settings
* **Printer** – Bambu Lab A1 (or any FDM)  
* **Nozzle** – 0.4 mm  
* **Layer height** – 0.20 mm  
* **Infill** – 15 % Grid  
* **Supports** – Not required  
* **Filament** – Any PLA; I used a silk‑copper PLA for a retro vibe

Files:
* case-bottom.stl  
* case-lid.stl

Both parts fit on a 180 × 180 mm bed.

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## Bill of Materials
| Qty | Part | Note |
|-----|------|------|
| 1 | Arduino Uno (clone OK) | ATmega328P |
| 1 | MAX7219 8 × 8 LED Matrix | FC‑16 module |
| 1 | 12 mm Momentary Push Button | SPST‑NO |
| 1 | 5 mm Red LED | Status light |
| 2 | 220 Ω Resistors | LED protection |
| – | Hook‑up Wires | Male‑to‑male jumpers |
| – | PLA Filament | 0.20 mm / 15 % |

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## Assembly
1. **Print** the two STLs—no supports or rafts needed.  
2. **Solder / connect** the matrix: DIN → D11, CS → D10, CLK → D13, VCC → 5 V, GND → GND.  
3. Wire the push button to D2 (interrupt) and the 5 mm LED + resistors to D3.  
4. Upload the firmware (see GitHub link below).  
5. Snap the PCB into the bottom shell, route the USB cable, and press‑fit the lid.

A full wiring diagram and commented code are included in the repo.

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## Firmware & Docs
All source files live on GitHub:  
**https://github.com/kocyunus/Reflex-meter**

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## Build Video
 

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## License
STLs and code are released under **MIT / CC‑BY** – remix, sell, or improve, but please credit the original project.

Tag your prints with **#ReflexMeter**; I’d love to see your fastest reaction times!