Curl tracker

Curl Tracker: Wearable Bicep Curl Coach

What is Curl Tracker?

Curl Tracker is a wearable bicep curl tracker that uses an ESP32-C3 Super Mini alongside a MPU-6500 IMU to count reps, measure curl speed, and evaluate form in real-time. It uses a on-device classifier to distinguish good reps from common curl form faults. Curl Tracker displays live rep metrics to a SSD1306 OLED and streams data over MQTT to be plotted on a Python/matplotlib client. It also provides haptic feedback and monitoring of device state.

Bicep-Curl Classifier

Training:

Collecting:

Breadboard Prototype

Design Choices:

• Power: 3.7V LiPo (range: 3.0V - 4.2V) with a TP4056 module for charging managment. MT3608 module converts the varying 3.7V Lipo to a stable 5V source. A mechanical switch is used as a on/off switch.

• MCU & Peripherals: ESP32-C3 Super Mini is the MCU that serves as the brain for the project. MPU-6500 IMU and SSD1306 share a I2C bus which the ESP32 uses to communicate. A push button is used to provide data collection input to label reps while gathering training data for the classifier.

• Feedback: A status LED exists which turns on if any of the electronic malfunction. The OLED displays rep count, sets, and status of MQTT. The vibration motor, paired with a flyback diode circuit for back-EMF protection, is used for haptic feedback.

KiCad Schematic & PCB layout

Design Choices:

• ESP32-C3-MINI-1 module: Using a pre-certified module means the RF design is already done and the FCC/CE certification carries over, so I avoid the antenna layout, matching network, and re-testing that a bare C3 would require.

• MPU6500 → BMI270: The MPU6500 is end-of-life and no longer recommended for new designs. The BMI270 is Bosch's current-generation IMU with active vendor support and drivers in most major frameworks.

• TP4056 → MCP73831: Swapped the TP4056 for Microchip's MCP73831. Better documented, properly sourced through mainstream distributors, and easier to justify in a design review.

• MT3608 → TPS63001: A LiPo swings from 4.2 V down to 3.0 V, which straddles the 3.3 V rail from both directions. A boost-only converter or an LDO can't hold regulation across that whole range, so the TPS63001 buck-boost keeps 3.3 V stable through the full discharge curve, including the current spikes when the ESP32's radio transmits.

• USB-C: The current connector standard: reversible, mechanically more durable than micro-B, and what any user will already have a cable for.

• JST-PH for battery and motor: Keyed housings so the connectors can't be seated backwards, and they're cheap, common, and rated well past the current this board draws.