ECG-based Exercise Monitor

ECG-based Exercise Monitor

Most exercise/fitness monitions today use optical means to detect the user's heart rate - a technique known as photoplethysmography (PPG). This is convenient and economical, but not terribly accurate.

The Client had developed a hardware platform using electrocardiography (ECG) - ie, sensing the electrical signals from the heart's activity - for greater accuracy of the heart rate measurement. A 3D accelerometer for motion sensing, and Bluetooth Low Energy (BLE)radio for communication with a mobile app, were also included.
Antronics Ltd assisted in developing the firmware for the STM32 ARM Cortex-M4 processor.

Our first task was to get the Nordic Semiconductor nRF8001 BLE radio working. Nordic provide an SDK in the form of an Arduino Library, so this had to be ported to "conventional" embedded 'C'.
We then devised and implemented the communication protocol used over the BLE link, for both operational data and development test modes

Another task was monitoring the battery charger, and "gas gauge" or "coulomb counter" to determine the battery's state of charge, and report this via the BLE link to the mobile app. Also, to detect when the battery level became critically low, and shut down the system to avoid over-discharge.

A considerable amount of time was spent in investigating and evaluating the various low-power "sleep" options of the processor and other components, and optimising power consumption so as to maximise battery life. This included developing some automated tests to record battery levels over a complete charge & discharge cycle.

We were also able to assist with hardware review and debugging of subsequent prototypes, and with research & suggestions for possible future versions.

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