Biomedical Engineering Reference
In-Depth Information
Fig. 6.8 An example of data
detection in the coordinator
node
Demodulated data
bits generated by the
FPGA module
Received IR-UWB
pulses from the UWB
front end
Sensor nodes are arranged such that their antennas are facing towards antennas of
the coordinator node.
Two ECG electrodes are used per continuous sensor node in order to obtain
ECG measurements. ECG signals are amplified and filtered using the analog front-
end circuitry in the sensor node. Inbuilt ADC of the micro-controller is used for
sampling the amplified ECG signal. Sampling of the ECG signals is carried out
during the sleep mode operation in between the data transmission. ECG signals are
sampled at a sampling rate of 8 kHz with a resolution of 10 bits per sample. This
generates 70 bits of ECG data per sampling cycle. Sampled data is buffered at the
micro-controller and sent during the next data transmission time slot using the
continuous data packet structure shown in Fig.
6.1
a. An on-board temperature
sensor that generates a 10-bit digital data output is used for the purpose of tem-
perature monitoring. Two temperature data samples buffered and transmitted every
10 s using the periodic data packet structure shown in Fig.
6.1
b.
Received data is stored at the coordinator node, and transmitted to a computer
terminal on request using serial communication. Data gathering and displaying is
handled using a program developed in Matlab [
10
]. A software based notch filter is
used to filter out the 50 Hz noise in the received ECG signal. Figure
6.9
depicts
the experimental set up used for the monitoring system. Figure
6.10
shows the
monitoring interface developed using Matlab. The random initialization of the
sensor nodes can be clearly observed in ECG waveforms shown in Fig.
6.10
.
