The main objective of the project was to create a wearable device, eg a shirt with a TFT display on it to Monitor the Heart Rate and the Pulse Wave of the person whose is wearing it.
The non-invasive heart rate monitoring consists of a pulse sensor which is used to acquire the analog signal and send it to the Arduino for processing. The signal displayed on the TFT display seen on the T-Shirt is the waveform from which the Beats Per Minute (BPM) is calculated.
The green LED light seen on the pulse sensor incidents light on the skin and the reflected light is incident on the photodiode
How to Use:
The wearable Heart rate monitoring sensor is really easy to wear. the sensor clips onto a fingertip or earlobe and plugs right into the Arduino.The Arduino and the TFT display used is fitted onto the t-shirt such that it is comfortably wearable. There is no risk of any electric shock as the current involved is very low. 3 easy steps to be followed,
- Wear the T-shirt
- Wrap the velcro which has the sensor around the index finger
- Plug in the battery
We can see the photoplethysmogram (PPG) waveform and our Heart rate in terms of BPM by following these simple steps.
- Portable and Small: One of the major advantages of this device over the currently available heart rate monitors it is lightweight and easy to carry. It is a wearable and highly mobile. It will not interfere with your daily activities or do not require any special precautions or measures.
- Low Maintenance: The device is really low in terms of maintenance. The only thing that is to be replaced is the battery, this can be done by using any 9V battery and do not require any special voltage supply. Sometime time the screen on the shirt or the wearable needs to be wiped using dry cloth, when the screen becomes foggy or if there is any dust. This can be done from outside the shirt without even removing the screen.
- Pulse Window: The Pulse Window feature allows the user as well as the attendant/doctor to monitor the pulse of the patient in real time. The Pulse Window is a dedicated portion of the screen with white background and pulse with a red line. This feature also helps to determine the P,Q, R and S on the pulse wave, which is significant for heart patient monitoring.
- Smart Alert Square: Smart Alert Square is one of the most important feature of the device. This square remains green when the pulse is normal as well as the BPM is in the safe zone. Once the pulse or the BPM goes off the range for more than 5 minutes, it turns read.This square is helpful in assisting people with non-medical background to warn about the situation or make a better decision whether it is an emergency or not.
- Configurable Safe Range Heart Rate Depending on the patient: This feature was added to the device considering the scenario that safe ranges for BPM may vary on person to person. For example the safe BPM range for an elderly is different from a teenager or may be depending upon the medical history the save BPM range varies. So to avoid the confusion, the doctor or the patient can configure this safe range. This will also help in avoiding false positive and false negative alarms.
Significance of the Pulse Graph:
The pulse sensor signal we display here is a photoplethysmogram (PPG), which is a way of non-invasive heart rate monitoring.The heart signal that comes out of a photoplethysmograph is a analog fluctuation of voltage, and its predictable and periodical.
The pulse sensor we use responds to relative changes in light intensity. If the amount of light incident on the sensor remains constant, the signal value will remain at 512 which is the midpoint of ADC range. More light and the signal goes up. Less light, the opposite. Light from the green LED (on the pulse sensor) that is reflected back to the sensor changes during each pulse.
Our main goal is to find the successive moments of instantaneous heart beat and measure the time between, called the Inter Beat Interval (IBI).We can achieve this by following the predictable shape and pattern of the PPG wave.
Generation of PPG:
When the heart pumps blood through the body, every beat produces a pulse wave which travels along all the arteries to the very extremities of the capillaries where the pulse sensor is attached.A rapid upward rise in the signal value is because the pulse wave passes under the sensor, then the signal falls down to the baseline level. Since the wave displayed has a repeating and predictable pattern, we can choose any reference point(Here we choose the peak of the wave) and measure the heart rate by doing the math on the time between each peak. Hence we can accurately do the calculation for the BPM.
The peak is counted for the calculation only when it crosses 50% of the amplitude and has the steepest slope. The IBI(Inter Beat Interval) is taken between every such peaks and the BPM is calculated from the average of previous 10 IBI times. How every step is calculated here is explained as comments in the code section.