Designing a Biosignal Extraction Device for Measuring a Blood Pressure

This paper presents a design of non-invasive electronic device for extracting a biosignal, with this device the extracted biosignal is then processed for measuring human blood pressure. The approach of the designed device is based on an oscillometric method. Leveraging on the potential of the electronic device, a cuff with a small sensor attaches to patient's forearm; the output signal of the sensor requires amplification and filtering operations in order to be applied into a microcontroller. Hence, the designed device consists of three parts: amplification circuit, filtering circuit and a microcontroller circuit. Signal amplification is performed using a level shifter to scale and shift the signal within a range of 0 to 5 volts, which is suitable for the work of the used microcontroller. Filtering off the noise from the extracted signal is done with a second order Butterworth band pass filter with bandwidth from 0.5 to 10 Hz. A microcontroller (PIC18F4550) is used for processing the signal and computing the result. The research investigates the accuracy of the extracted biomedical signal computation to achieve good result for helping both healthy people and patients to self-monitor their wellness.