How can a digital sphygmomanometer be made?

How can a digital sphygmomanometer be made?

In this article, we will evaluate how to make a digital blood pressure monitor. As is known, sphygmomanometers were a device with mechanical parts and worked by creating air pressure in earlier times. With the development of sensors, digital blood pressure monitors have been in our lives for a long time.

This article was written as a guide for project developers in the medical-health field. We wanted to guide developers who are curious about developing electronic-medical devices by including such technical articles from time to time on our site.

Earlier, we made an app for heart rate measurement. We received the heart rate data with the help of a heart rate monitor connected to the microcontroller and sent it to the Android phone with the help of the bluetooth module. With the Android application we developed in Flutter-Dart language, we showed the data we received from the bluetooth adapter on the phone screen. Link: A BlueTooth-controlled Android App to Measure Heart Rate - Electronics World News (milivolt.news)

Before going into details about digital sphygmomanometer design, let's explain the concept of blood pressure.

What is tension?

Blood pressure is the pressure at which blood is pumped by the heart into the arteries. Blood pressure depends on the pressure exerted on the arterial walls and the dilation of the arteries. Blood pressure varies depending on the time interval between heartbeats and how many times the heart beats per minute.

Blood pressure is measured as upper or systolic blood pressure and lower or diastolic blood pressure. Upper blood pressure is the highest pressure applied to the arteries when the heart muscle contracts, and diastolic blood pressure is the lowest pressure applied to the arteries when the heart muscle is relaxed.

Blood pressure is measured in mmHg (millimeters of mercury) and is normally considered 120/80 mmHg. However, factors such as age, gender, physical activity, stress, eating and drinking can affect blood pressure levels. High blood pressure, or hypertension, results from the high pressure applied to the arteries and can lead to health problems such as heart disease, stroke, and kidney disease. Low blood pressure or hypotension occurs when there is insufficient blood flow and can cause symptoms such as dizziness, fainting, and fatigue.

What is the working principle of Digital Sphygmomanometer?

Digital blood pressure monitors work non-invasively, that is, without interfering with the blood circulation. The instrument includes a cuff that wraps around a body area such as an arm or wrist, and a sensor attached to the cuff.

Blood pressure measurement begins with cuff inflation. The inflation process increases the air pressure in the cuff, preventing arterial blood flow and accordingly increasing the pressure in the artery in the arm. When the cuff reaches a certain pressure level, the sensor is used to measure blood pressure.

As the cuff is slowly deflated, the sensor measures changes in blood flow and these changes are used to measure blood pressure. These measurements are then processed by the microcontroller and the results are displayed on the screen or other output devices.


Barometric pressure sensors are used to measure pressure values. In blood pressure monitors, these sensors are used in the cuff and are used to measure pressure. Sensors such as BMP280 or BMP180 send data to the microcontroller via the I2C interface, and the microcontroller processes the measured values and performs the blood pressure measurement.
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What is the BMP180 sensor, barometric pressure and temperature sensor?

The BMP180 sensor is a sensor used to measure barometric pressure and temperature. This sensor is manufactured by Bosch Sensortec and communicates via a digital interface. The BMP180 is a more advanced version of the BMP085 sensor, providing higher resolution, lower power consumption and higher measurement accuracy.

bmp180 sensor

The output of the sensor is read through the I2C (Inter-Integrated Circuit) protocol. The BMP180 uses a thermistor for temperature measurement and a piezoresistive sensor for pressure measurement. The pressure measurement is done by the microprocessor on the sensor and the results can be read digitally with 16-bit resolution. The sensor operates in the range of 300 to 1100 hPa for pressure measurement and -40 to 85 degrees Celsius for temperature measurement.

The BMP180 sensor is often used in various projects such as air pressure measurement, air quality measurement, altitude measurement and meteorological applications. It is also used for altitude measurement of aircraft such as drones and unmanned aerial vehicles.

Digital Sphygmomanometer Project Components

Making a blood pressure device requires a very sensitive process and therefore it cannot be expected to provide accurate results that can only be achieved with professional medical devices. However, it is possible to measure your blood pressure by building a simple prototype with an Arduino. Here are the basic steps:
Arduino UNO or Nano
BMP180 Barometric pressure sensor
Servo-motor
LCD screen
breadboard
jumper cables
9V battery or USB cable
Computer


Steps:

Connect the VCC pin of the BMP180 sensor to the 3.3V pin of the Arduino, the GND pin to the GND pin, and the SDA and SCL pins to the A4 and A5 pins.


Connect the VCC pin of the servo motor to the 5V pin, the GND pin to the GND pin and the signal pin to the 9th pin.


Connect the LCD screen to the GND, VCC, SDA and SCL pins.


Inflate a cuff using a servo motor and then slowly deflate to measure blood pressure.

Read blood pressure readings using the BMP180 sensor.

Display the blood pressure values and the position of the servo on the LCD screen.


Write the codes and upload them to Arduino.

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In this article, we touched on the basics that we need to know before we go into practice. After the implementation of the first stage, the next stage can be passed. The second step will be to display the blood pressure data coming from the bluetooth module on the screen with an Android application, as in the Pulse Meter-Heart rate meter application that we mentioned at the beginning of the article.


In fact, it may seem like enough to show the blood pressure data on the LCD screen connected to the microcontroller, but with the Android application, add-ons such as regularly recording the blood pressure data and reporting it later increase the usefulness of our project.