TinZr: A compact wireless ESP32-C3 platform for multi-modal physiological sensor integration and data acquisition

Microcontrollers have become central to wearable technologies. As these systems continue to evolve, both form factor and functional integration have become critical design considerations. In this study, we present TinZr, a compact, wireless, and open-source ESP32-C3-based microcontroller that serves as a central hub for interfacing with external sensing modules, data logging, and wireless transmission. The TinZr integrates an inertial measurement unit (IMU), an onboard battery management circuit, Wi-Fi and Bluetooth Low Energy, a microSD card reader, and multiple GPIOs supporting digital, analog, I²C, SPI, and UART interfaces. The complete system measures only 25 mm × 25 mm, making it well-suited for wearable applications. All production files, including printed circuit board (PCB) design, firmware, and a 3D model of a wearable enclosure, are publicly available. Three primary use cases for TinZr are demonstrated: (a) multi-device communication and coordination, (b) wireless IMU data acquisition, and (c) simultaneous multi-modal physiological signal acquisition using external electrocardiography (ECG) and photoplethysmography (PPG) sensing modules. The TinZr supports both real-time data streaming via Wi-Fi/BLE and local logging to a microSD card. Local logging makes the TinZr suitable for extended research experiments and field studies where continuous wireless connectivity may not be available. An accompanying Arduino library, TinZrConnect, is provided to facilitate programming and integration with existing systems. Overall, the combination of compact design, wireless flexibility, and open-source accessibility makes TinZr a versatile solution for various sensing applications.