The principle of blood pressure measurement is based on the force exerted by circulating blood against the walls of blood vessels. As the heart contracts, it pumps blood through the arteries, creating a pressure known as systolic blood pressure. When the heart relaxes, the pressure in the arteries drops, which is referred to as diastolic blood pressure. During a blood pressure reading, an inflatable cuff is placed around the arm and gradually deflated. The point at which blood flow resumes and the first sound is heard corresponds to the systolic pressure, while the last sound marks the diastolic pressure.
Electronic sphygmomanometers operate using a series of circuits that work together to measure and display blood pressure accurately. The system typically includes a constant current source, a pressure sensor, amplification circuits, filters, and a microcontroller. These components collaborate to detect and process the pressure signals from the cuff. The microcontroller controls the inflation and deflation of the cuff, processes the data, and displays the results on an LCD screen. It also supports voice prompts and alarms for abnormal readings, making it user-friendly and suitable for home use.
The hardware design of the device centers around the MSP430F449D microcontroller, which manages the entire operation. This microcontroller handles tasks such as controlling the air pump, sampling pressure signals, and processing data. The system also includes a pressure sensing circuit with a BP01 sensor and an operational amplifier (MAX4472), ensuring accurate detection of both DC and AC components of the pressure signal. Additional circuits include filtering and amplifying stages, a real-time clock and memory module, a keyboard interface, a display, and a voice alarm system.
The filtering and amplification circuit uses a MAX267 bandpass filter to isolate the relevant pressure signals, removing noise and interference. The amplified signal is then processed by the microcontroller to determine systolic and diastolic values. The real-time clock and memory module (using EEPROM 24C256 and PCF8563) allow the device to store previous readings along with the date and time, enabling users to track their blood pressure trends over time.
The keyboard and display interface provide an intuitive way for users to interact with the device. A 128x64 dot-matrix LCD shows key information like systolic and diastolic pressure, current time, and historical data. The seven-button keypad allows users to navigate through settings, view stored data, and adjust parameters. Additionally, a voice chip (ISD2560) offers audio feedback, and an alarm system alerts users if their blood pressure falls outside normal ranges.
This electronic sphygmomanometer is designed for ease of use, portability, and accuracy. With low power consumption and intelligent features, it is ideal for home monitoring, especially for individuals with hypertension or older adults. Its compact design and advanced functionality make it a valuable tool in modern healthcare, offering convenience and reliability for daily use.
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