To ensure that our aesthetic design ambitions were realistic we designed the circuitry required by the device to allow us to accurately assess the space requirements needed.
From the start we knew that battery size and capacity would be one of the biggest hurdles for us to overcome to make the device useful and hassle-free for users. As one of our priorities was to minimise the mass that needed to be placed on a user’s ear, we made the decision to sacrifice battery capacity and install a wireless charging system, allowing the system to have almost continuous power supplied from an easily accessible source. This system allows the primary device power to be supplied externally, but also provides a small battery to act as a buffer, ensuring continuous data collection and transmission is maintained.
To further minimise the size of the ear–based unit we installed a combined bluetooth and processor system on chip. To measure heart rate and SO2 levels, the chip (A Nordic Semiconductor nRF52832) pulses an IR LED into the blood vessels behind the wearer’s ear. The reflected signals from this diode are then picked up by an IR detector, where changes in light intensity are converted to a varying voltage signal. This signal is then amplified by an Op-amp, operating in non-inverting amplification mode, and fed into an input on the nRF52831. The signal is sampled by the nRF52831 and temporarily stored in memory before being transferred via BLE (Bluetooth Low Energy) to the user’s smartphone or to central medical server.
The circuit board is designed in a unique trapezoidal shape. In addition to the 3 mounting holes present on the board, this shape ensures the PCB is firmly secured inside the earpiece casing, ensuring the system’s longevity.