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2. ENGINEERING AND TECHNOLOGY, Electrical and electronic engineering, Communication engineering and systems
The conventional biopotential measurement configuration utilises long lead wires which connect measuring electrodes to signal conditioning circuitry. The majority of bioelectric signals that are measured from the human body have a tiny signal amplitude (5µV-5mV range) and thus any interference that is induced on the lead wires can have a detrimental effect on the original signal. In this paper, we present an alternative configuration, in which digitisation occurs on the electrode, potentially providing enhanced signal measurement as well as significant benefits in terms of the simplification of the physical interconnections between electrodes. Multiple electrodes are combined to form a digital electrode bus. This proposed topology represents the next stage in the evolution of bioelectric measurement as, due to the decrease in cost and size of integrated circuits, more of the bioinstrumentation circuitry is shifted away from a base measurement station and into the electrode itself. The prototype wireless device outlined in this paper consists of a grid of electrode nodes. By adding a circuit weighing less than 0.45g and with a diameter of 1.5cm to standard button clip electrodes, each node contains a high resolution analog-to-digital converter, and a microcontroller. With this design, the lead length has been reduced to a copper PCB track with dimensions of less than 3.5x0.3mm. All of the nodes are connected onto a shared I2C bus on which a master node synchronises slave electrode sampling and coordinates inter-device communication. The system is currently capable of a 215 Hz sampling rate (for one node at 16-bit resolution) with a limit of up to 79 nodes connected. The system has been demonstrated to work on the electrooculogram and the electrocardiogram and the results for these have been outlined.
Nolan, P., Burke, E., & Coule, E. (2012). A Wireless and Digital Electrode Bus Topology for Biopotential Measurement. Irish Signals and Systems Conference (ISSC 2012), NUI Maynooth, Ireland. doi:10.1049/ic.2012.0214