A US based company specialized in interactive health management and remote patient monitoring systems, wanted to design a Gateway product to connect with low power RF medical devices. This gateway device at the patientâ€™s home enabled data from personal health monitoring devices to be sent to an open list of data exchange servers.
The gateway device provides connectivity to the data server located on the Internet, to various Personal Health Devices (PHDs) at home. The gateway provides different uplink options to connect to the data server. This includes PSTN using a dial up mode, Ethernet for a broadband connection to the server and through smart phones using a Bluetooth link. On the downlink connection to various PHDs, the gateway provides option of connecting via its two USB ports (serial COM connection), ANT+ interface and Bluetooth LE (BTLE) interface. The Gateway user interface is through LEDs, a two line LCD display with a button.
The Gateway was powered using Battery. The Gateway will connect to server upon user initiation. It will parse commands from the server and will upload data from PHD. The communication supported multilingual PHD medical devices. The Gateway had inbuilt POST (Power on Self Test), diagnostics and logging firmware. The results were uploaded to server based on specific requests. The Gateway used a 32 bit PIC processor from Microchip. It communicated with other on-board modules ANT+, BT LE, Ethernet, USB and PSTN using I2C and SPI serial communication interfaces.
The firmware was designed using layered approach and in a modular way with clean interfaces between the modules so that it shall be possible to upgrade the system easily. As the number of modes of operation, states, events and tasks are limited; the system was implemented using a simple custom scheduler. Each of the major tasks will be executed sequentially and where necessary, scheduled periodically or on event basis using a simple scheduler embedded in the main module. Asynchronous events (e.g., button press, or communication events or timer events) were handled in interrupts as appropriate and a notification mechanism was employed to handle such transaction within the layer or the module.
The challenge was to design Gateway with very low BOM cost with various plug and play options to support different types of wireless/wired communication technologies to medical devices as well as different ways of uploading data to server using broadband connection.