OCELOT. A USB-Based Industrial I/O Board for Cash Deposit Systems

Abstract

Commercial off-the-shelf (COTS) I/O boards offer a convenient solution for embedded applications; however, they often incorporate unnecessary features, increase hardware dependencies, and complicate software integration. To address these limitations, this paper presents the design and implementation of the OCELOT I/O board, a custom embedded platform developed to replace the commercial Numato I/O board currently used in the RC-200 and RC-300 cash management systems. The proposed solution combines dedicated hardware with a layered RTOS-based firmware architecture. The firmware adopts an event-driven architecture that decouples communication, command processing, and hardware control, providing a modular and scalable software design. It implements a communication and control framework comprising a JSON-RPC host interface, dedicated drivers for digital inputs, digital outputs, and RGB LED control, together with a USB UF2 bootloader that enables firmware updates through a standard USB Mass Storage Class (MSC) interface. Functional validation verified the correct operation of the communication subsystem, peripheral drivers, and firmware update mechanism. The proposed platform demonstrates that a purpose-built embedded solution can successfully replace the previous commercial hardware while simplifying software integration and supporting future firmware expansion.