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  • Digital Blood Pressure Meter using PIC24F Microntroller

  • Created: Jan 23, 2017

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Most people prefer a non-invasive health monitoring than invasive technique. This is because non-invasive devices do not require the skin to be broken or a cavity or organ of the body to be entered, for obtaining a blood pressure reading by auscultation with a stethoscope and sphygmomanometer. This design presents a digital blood pressure meter using PIC24FJ128GC010 microcontroller from Microchip. This meter measures systolic and diastolic pressures by oscillometric detection. This design measures blood pressure and pulse rate during inflation. The Measurement While Inflating (MWI) principle reduces overall measuring time, which in turn reduces discomfort caused by the pressure in the cuff.

This circuit is supplied by 4 1.5-V AAA batteries. It is then regulated by MCP1802 to get a 3.3V output. A 5V 500mA is also acquired from the 6V battery for USB supply. The MCP6N16-100 single Instrumentation Amplifier (INA) is used to condition the analog signal acquired from the Wheatstone bridge type of air pressure sensor. The output signal of the MCP6N16 is split into two paths. One path, representing the cuff pressure, is connected to the ADC1 channel of the microcontroller. Another path is passed through a 2-pole active high-pass filter, which outputs the oscillation signal that is sent to the ADC2 channel of the microcontroller. The microcontroller PWM module drives the air pump’s motor in fast or slow speed mode. After the motor pumps the pressure up to 30mmHg in fast mode, the motor changes to slow mode gradually and linearly inflating the cuff. When the pressure in the cuff gets high enough to just begin constricting the flow of blood, the arterial pulse becomes detectable by the pressure sensor. The inflation process is automatically terminated when the pressure reaches a specified value. The microcontroller provides a 12-bit high-speed pipeline ADC. The cuff pressure signal and the oscillation signal are both sampled at 250Hz through a 12-bit ADC. Microchip’s mTouch sensing solution is implemented in the firmware for the capacitive touch pads utilizing the microcontroller’s Charge Time Measurement Unit (CTMU). Meanwhile, the air pressure sensor requires a stable supply current of which is also provided by the CTMU.

The blood pressure and pulse rate results are sent to an LCD panel, USB interface as well as wireless interface. The microcontroller has an integrated LCD controller that generates the data and timing control required to directly drive an LCD panel. The design also utilizes the microcontroller’s USB On-The-Go interface for data communication as well as the 5V main power source. For wireless communication, the microcontroller’s SPI or UART port connects to a Microchip RN42 Bluetooth module or an RN171 Wi-Fi module.