A round timer for martial arts/boxing/whatever.
This project is a compact, battery-powered round timer designed for martial arts classes like judo. It uses an Adafruit Trinket M0, an I2C alphanumeric LED display, and a piezo buzzer to provide audible round signals. This is used by us at https://austinjudo.club
I've included the FreeCad file for the box.
I need distractions while I'm working on my AI Stock Trader at https://ai-stocktrading.com
- Selectable round durations: 30, 45, 60, 120, 180, or 300 seconds
- Start/Pause button with audible feedback
- Looping rounds: automatically restarts after each round ends
- Onboard RGB LED flash and buzzer at round end
- Volume control via button combo
- Sound style selection via button combo (10 unique sounds)
- 3-digit countdown display
- Sleep mode after 5 minutes of inactivity (wakes on button press)
- Stores settings (volume, interval, sound) in onboard flash
- Powered by a 3.7V LiPo battery with a USB charger
- Runs for many sessions on a single charge
| Component | Purpose |
|---|---|
| Adafruit Trinket M0 | Main controller |
| https://www.adafruit.com/product/3500 | |
| Adafruit Alphanumeric Display | 4-character countdown display (I²C) |
| https://www.adafruit.com/product/879 | |
| Piezo buzzer w/ driver | Audible round signal |
| https://www.adafruit.com/product/5791 | |
| USB LiPo charger | Recharge battery between classes. |
| https://www.adafruit.com/product/1905 | |
| Power switch | Power off between classes. |
| 2x pushbuttons | Mode and Start/Pause |
| LiPo battery (3.7V) | Power source |
| Trinket M0 Pin | Connected Device |
|---|---|
| BAT | LiPo Battery + |
| GND | Battery –, display GND, button GNDs |
| 3V | Display VCC |
| 0 (SCL) | Display SCL |
| 2 (SDA) | Display SDA |
| 1 | Buzzer IN |
| 3 | MODE button |
| 4 | START/PAUSE button |
| 7 (DotStar DI) | Onboard RGB data (internal) |
| 8 (DotStar CI) | Onboard RGB clock (internal) |
| Action | Result |
|---|---|
| Tap MODE | Change duration or reset if running |
| Tap START | Start or pause timer |
| Hold START, tap MODE | Cycle volume 1–9 |
| Hold MODE, tap START | Cycle sound style (0–9) |
Settings are saved using FlashStorage:
- Volume: 1–9
- Interval: 0–5 (maps to 30–300 seconds)
- Sound index: 0–9
- Sleeps after 5 minutes of inactivity
- Wakes instantly on any button press
- RGB and buzzer are disabled while asleep
This project is licensed under the MIT License. Feel free to modify and reuse!
- Adafruit for their Trinket M0 and display libraries. Lady Ada is awesome!
- Arduino for platform support
- The students of Austin Judo Club 🥋 https://austinjudo.club