WEEK 1

WEEK 1

This smart sports watch has two main functions. First, it can detect the user's heart rate. When users are exercising, paying attention to their heart rate can better protect and regulate themselves. Next, it can detect the user's steps. For sedentary people, it plays a role in urging themselves to exercise.

Heart Rate Measurement  

The aim is to build a heart rate measurement using the LED and photoresistor without a pulse sensor to measure the heart rate on the finger. The materials we intend to use are photoresistor with maximum sensitivity about 650nm and Red LED with 10000mcd brightness.

The principle we refer to is as follows. A heart rate is formed by two parts, the systole and the diastole. One heart rate will be measured after a systole and diastole is finished. The systole is the process that the blood is pushed to the body from the heart, conversely, the diastole occurs as blood flows back to the heart from the body. This project measures heart rate by collecting and managing the data of the differences of the blood. The blood in systole is lighter than the blood in diastole because blood carries oxygen from the heart to the rest of the body by systole and the blood in diastole is out of oxygen. When a red LED is shining beside the finger, the red light will be absorbed by the blood in either systole or diastole. Because the absorbance of blood in systole and diastole is different, each change of the direction of the blood occurs the change of the brightness which result in the change of the resistance connected with the LED. The software will operate with this change and analysis as a heart rate.

The method we intend to use is as follows. The sensor consists of LED and photoresistor will be created to measure the heart rate. The LED and photo resistor will be parallel connected. The voltage of the resistance will be detected. The raw data gathered from the heart rate sensor will be unusable because of the low magnitude of the signal. A filter will be used to acquire usable voltage. With the consideration, the frequency of the heart rate signal would be 1Hz to 3Hz. So a band-pass filter will be used. With the more stages of the use of the filter, the more accurate signal will be acquired. After the data collection, the data will be operated in software. Each peak of the voltage will be considered as a pulse. With the calculation of the frequency and the amount of the heart rate, the amount of the heart rate per minute will be calculated and presented to the user.

Summary:
For the first day, we aimed to construct a initial circuit to test the availability of the photoresistor and the output from oscilloscope
Result: we formed a circuit with a band-pass filter to get the output from 1Hz to 3Hz, but the output is still no so desirable and we found that we made a mistake in calculating the value of the capacitors. So, after that day, we re-construct a circuit for it.
Improvements：
1. The output is still not applicable; more test is needed.
2. We need to eliminate the effect from ambient light, which means we supposed to use sponge tape with good shading ability to form a bandage-like container to :wrap the photoresistor and the LED

Pedometer 

Through the process of design, we chose the Triple-Axis Accelerator which model is “Adafruit 1231 ADXL345” as the main component for the developing of the pedometer. The basic mechanism for ADXL345 is that it measures static or dynamic acceleration along its three axes x, y and z. According to the research done by Neil, due to at least one axis will have relatively large periodic acceleration changes whatsoever the direction of the component is placed, it means that the peak detection and a dynamic threshold-decision algorithm for acceleration on all three axes will be utilized to detect one unit step. In other words, the working principle of it is consisting of four algorithms: peak detection, dynamic threshold-decision, time window and count regulation.
1. For the algorithm of peak detection, it chooses the axis with the largest amplitude (largest acceleration changes) as the forward direction.
2. For the algorithm of dynamic threshold-decision, if there is a negative slope of the acceleration plot when the dynamic threshold (half of the addition of maximum and minimum value of the 3-axis acceleration) is over the acceleration curve, which means the new sampled acceleration is smaller than the old sampled one, one step is defined.
3. For the algorithm of time window, limiting the time interval between every two steps to discard the invalid vibrations. Step within the time interval will be regarded as a valid one.
4. For the algorithm of count regulation, the program starts to search regulation when there are continuous valid steps for better counting steps. Rediscover regulation when there is an invalid step detected.

Therefore, we decided to use an Arduino board and a LCD screen with this component to realize the function. Though the process of building the prototype, first we decided to connect all these components by DuPont cables and soldering them together to form a circuit. Then, developing the codes for the above-mentioned four algorithms and writing them into the Arduino board to analyze data received from the output of the 3-axis accelerator to count steps and then display the results on the LCD screen. The step can be detected by shaking the component with proper amplitude.

Summary:
For the first day, we followed the tutorial from the Rapid tested its availability by using the off-the-shelf code.
Result: 
We have successfully tested it and we find that its output is in the unit of s/m^2, which means that it must contains the acceleration of gravity.
Improvements: 
1. The circuit is still in its basic form; we may need to add some resistors to get a better output.
2. We need to form an algorithm to analyze the output

LCD Display

For the first day, we aimed to test its availability 

Result:

At the beginning, the display displayed wrong output as we used the test code for 1602A, we didn't find any test code for this component. Then, after modified the code several times, we finally obtained the correct output.

Improvements:

1. We started to develop a program for timer and display variable outputs on the screen. 

2. The power supply for the screen can be improved.