Bluetooth smart Bracelet system based on STM32 MCU

This smart Bracelet system includes the following ： Step number record 、 Take your temperature 、 Heart rate measurement 、RTC Real time clock 、APP Look at the relevant data

Main hardware procurement links ：

stm Minimum system board	https://m.tb.cn/h.fNy7pcW?tk=XKLr2f8YwWD	Third package
BT06 Bluetooth module	bluetooth 3.0 modular SPP transparent transmission compatible HC-05/06 Slave JDY-31 Bluetooth module -tmall.com Tmall
ADXL345 Acceleration sensor module	ADXL345 ADXL335 Digital The acceleration tilt angle sensor module senses Send information -tmall.com Tmall	The second set meal
Pulse Sensor Heart rate sensor	1pcs pulsesensor pulse heart rate sensor open source hardwar- TaoBao (taobao.com)	The first set meal
DS18B20 Temperature sensor	DS18B20 chip Programmable digital thermometer / Temperature sensor TO-92 Direct insertion new - TaoBao (taobao.com)
IIC 4 The needle OLED	0.96 " OLED display SSD1306 Drive LCD 4/7 The needle IIC/SPI The interface is white, yellow and blue -tmall.com Tmall	Third package

These purchase links are just for your reference , Be careful when shopping .

One 、 Physical display

  Two 、 Principle explanation

1、 Heart rate measurement function

         Heart rate refers to the number of heart beats in a minute , The dumbest way to get your heart rate is to count the number of pulses in a minute . But in this way, every time the heart rate is measured, you have to wait for a minute before you get the result , Extremely inefficient . Another way is to , Measure the time interval between two adjacent pulses , Divide that interval by one minute to get the heart rate . The advantage of this is that the pulse can be calculated in real time , Efficient . This leads to IBI and BPM The concept of two values ：IBI： The interval between two adjacent pulses （ Company ：ms） 

                                                                     BPM： heart rate , The number of heart beats in a minute

  be BPM = 60 / IBI

Here is how to detect heart rate ：

The primary goal is to recognize a pulse signal （ Because only by finding the pulse signal can time be calculated ）

                                                                 

Identify the pulse by detecting the peak

                           （ How to find the crest ）

Set a threshold to judge the peak

（ When the analog signal exceeds the set threshold , It is considered to have reached the peak ）

                                                               （ How much threshold should be set ？ It can be a fixed value ？）

The threshold cannot be a fixed value , Dynamic threshold needs to be set

                                                                          （ Multiple acquisition , Find the maximum 、 minimum value , Perform relevant calculations ）

Dynamically calculate the threshold

         As for why the threshold cannot be set to a fixed value , Need to set dynamic threshold ？ Because people have different pulse intensity at different times , It cannot be measured by a fixed value , Therefore, it is necessary to calculate the appropriate threshold at the current time , As shown in the figure below .

  therefore , The measurement of pulse signal is divided into two steps ：① First calculate the reference dynamic threshold

                                                        ② Use the dynamic threshold to judge the peak , So as to find the wave crest

Find the pulse waveform , Calculate the time of two adjacent times

         This design adopts the method of feature points , Define the signal rising to half of the amplitude as the characteristic point , In this way, the time interval between two characteristic points can be measured to obtain the time interval of two adjacent pulses .

  As shown in the figure , The time interval between two adjacent feature points is IBI, And then use 60/IBI Is the heart rate .

2、 Number of steps

For the detection of the number of steps , Most designs use pressure sensors , This design adopts acceleration sensor , With “ The acceleration ” For related parameters , More research significance .

         As shown in the figure ,ADXL345 The acceleration sensor can detect the acceleration in the three-axis direction , Among the features that can be used to analyze running or walking , We choose “ The acceleration ” As relevant parameters . individual ( And its related axes ) The motion of includes three components , They are forward (“ rolling ”)、 vertical (“ Yaw ”) And lateral （“ pitch ”).

        Pictured , Let's consider the characteristics of walking . A step , We define it as the unit walking cycle . Walk with your left foot ( Shadowy ) Will produce corresponding acceleration , Speed up 、 Decelerate and reciprocate , And there will be a peak at some point . Through the capacitive voltage converter 、 Gain amplification 、 After filter and temperature compensation Voltage signal output similar to sinusoidal waveform .

  As shown in the figure ： Get waveforms in three directions , but Y The shaft waveform is stronger , The explanation is along Y Axis forward .

The rising edge of the waveform represents the acceleration rise , That is, people step on their legs ; The falling edge of the waveform represents the decrease of acceleration , That is, people close their legs .

3、OLED The screen shows

  This project develops display function , The screen has two displays ： One shows the perpetual calendar , Second, it shows the heart rate 、 They count 、 Temperature , Both displays use buttons K0 Switch .

        ① Display the perpetual calendar ： By clicking K0 Switch to the time interface , When the time is wrong , Clickable K1 Press the key to enter the time setting interface , Press repeatedly K1 Set the year in chronological order 、 month 、 Japan 、 when 、 branch （ That is, by pressing the key K1 Set the time in different units , There are arrows in the screen >, Indicates the unit currently being set ） And then through K2、K3 Press the key to modify the time .

        ② Show physical status ： When the sensor detects body temperature 、 They count 、 When indexes such as heart rate change , Update in real time , And every day 0：00 It will clear the number of steps , You can also use K2 Press the key to reset manually .
 

                            

      Physical condition display interface                                      Real time clock                                         Time setting interface

 4、APP View the data

  This design uses Bluetooth to transmit data , See the previous article about Bluetooth HC-05（ZS-040） Bluetooth module usage details （ Mobile phone and Bluetooth module 、 Mobile phone Bluetooth control MCU 、 Communication between a pair of Bluetooth ）_ The poorest is begging for food 、 The blog that never dies will come out -CSDN Blog _zs040 How to use Bluetooth module

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5、 Thermometry

This design chooses 18b20, It's simpler , I won't repeat .

  Welcome to correct and exchange , You can discuss the code together when you are free .

It's not easy to make , Thank you for your support , thank ！！！！！！

  -------------- A person who is working hard