# Sixth Lichuang Electric Competition# Portable wireless ECG equipment

Note: * is required

Please fill it out during the registration stage↓

* 1. Introduction to project functions

Nowadays, life is fast-paced and stressful. People often ignore paying attention to body signals and are prone to sudden death. In fact, these can be prevented in advance, for example, monitoring heart rate is one way. Cardiovascular disease is a very important cause of sudden death. However, current ECG monitoring equipment either has too many connections, which affects normal life and work, or is expensive. This project aims to make a low-cost, wireless heart rate monitoring ECG device that can perform 24-hour heart rate monitoring.

Note: There is no limit to the theme. It can be a solution to a certain problem in life/work, a plan designed for a certain group of people/scenarios, graduation project/course design/DIY project/purely cool project, etc. Mainly talk about what problems you solved by what means.

*2. Project attributes

This project is my own creation and is published for the first time. I have not participated in competitions or school defenses.

Note: Please indicate whether the project has been made public for the first time; whether the project is original; whether the project has won awards in other competitions; if so, describe the details of the award; whether the project has participated in a defense in school.

* 3. Open source agreement

GPL3.0

Note: Altruism means self-interest, please read the following content carefully.

1. Embrace open source and give projects unlimited value. It is recommended that more than 80% of the core functions of the project be open source;
2. If a certain part of the function is irreplaceable and the project cannot solve the corresponding problem after deletion, then the function implemented by this part is the core function of the project; for example, if an electronic load is designed and a host computer software is designed to monitor power changes, the electronic The load is the core function, and the host computer software is the auxiliary function; for example, an isolated 485 module is used in the electronic load to communicate with the host computer, then the communication function implemented by this 485 module is an auxiliary function;
3. Projects should choose an open source agreement that suits them . If the project references other open source projects, the source should be indicated and follow the original author's open source agreement. It is recommended that original projects use the GPL3.0 open source agreement;
4. Functions implemented by directly quoting the original circuits or original codes of open source projects cannot be used as the core functions of one's own projects, and functions directly implemented using common modules on the market cannot be used as core functions of one's own projects.

Please fill in during the competition stage↓

*4. Hardware part

The hardware mainly consists of 3 parts: ECG, BLE, and power supply. The hardware block diagram is shown below:

4.1 ECG part

The original ECG signal (0.1~2mV) is amplified 1000 times through a precision instrument amplifier, and then the 50Hz noise interference is filtered out through a band-pass filter composed of a low-pass filter and a high-pass filter.

The instrumentation amplifier is AD8420 from Analog Devices. The AD8420 is a low-cost, wide-supply-voltage amplifier product whose gain can be set to any value between 1 and 1000 using two resistors. The device is optimized for amplifying small differential voltages in the presence of large common-mode signals and has excellent input common-mode range, based on a current-mode architecture. Unlike conventional instrumentation amplifiers, the AD8420 can easily amplify signals at or slightly below ground without requiring dual power supplies. The AD8420 has a full-range rail-to-rail output whose output voltage is completely independent of the input common-mode voltage. The typical application circuit is shown in the figure below:

The filter uses AD8657 from Analog Devices. The AD8657 is a dual-channel micropower, precision rail-to-rail input/output amplifier optimized for low power and wide operating supply voltage range applications. Typical quiescent supply current is 18 μA. This type of device uses Analog Devices' patented DigiTrim® adjustment technology, which has very low offset voltage and high immunity to electromagnetic interference. Another channel of the AD8657 feeds the output of the ECG and the right leg drive input to the reference of the instrumentation amplifier, further suppressing noise interference. The typical application circuit is shown in the figure below:

Since the ECG part has positive and negative voltages, and the ADC of the BLE part can only convert positive voltages in the range of 0~3V, AD8531 is used to form an adder to convert the ECG signal to +1V. This facilitates the ADC to sample the ECG voltage. The AD8531 pin diagram is shown below:

4.2 BLE part

The main control part uses Fengjia Micro’s Bluetooth SOC chip PHY6212. PHY6212 is an ultra-low-power IoT Bluetooth wireless communication chip equipped with a 32-bit ARM® Cortex™-M0 CPU and equipped with 138KSRAM/Retention SRAM. It has the characteristics of ultra-low power consumption, high performance and wireless multi-mode, and supports security , applications and over-the-air updates for BLE functionality. At the same time, its serial peripheral IO and integrated application IP will also bring low-cost advantages to customers.

The analog signal output by the ECG part is converted into a digital signal through the chip's own ADC, with a sampling rate of 250Hz. In addition to the ECG signal, the analog-to-digital conversion through the ADC also includes the battery power and the base reference voltage. Then transmit it to the host computer through BLE wirelessly. The minimal system is shown below:

4.3 Power supply part

The power part is powered by a 3.7V lithium battery with a charging voltage of 5V and can be accessed through the MicroUSB interface. The voltage regulator chip outputs 3V voltage to power the ECG and BLE parts. The voltage inverter outputs -3V voltage to power the ECG part.

The charging part uses Nanjing Tuowei’s TP4054. The TP4054 is a complete single-cell Li-ion battery with constant current/constant voltage linear charger. Due to the internal PMOSFET architecture and anti-backup circuitry, external sense resistors and isolation diodes are not required. Thermal feedback regulates charge current to limit chip temperature during high-power operation or high ambient temperature conditions. The charging voltage is fixed at 4.2V, while the charging current can be up to 800mA, externally set via a resistor. When the charging current drops to 1/10 of the set value after reaching the final float voltage, the TP4054 will automatically terminate the charging cycle. When input voltage (AC adapter or USB power) is removed, the TP4054 automatically enters a low current state, reducing battery leakage current to less than 2uA. The TP4054 can also be placed in shutdown mode to reduce the supply current to 45uA. Other features of the TP4054 include a charge current monitor, undervoltage lockout, automatic recharge, and a status pin to indicate end of charge and input voltage input. The typical application circuit is shown in the figure below:

The voltage stabilizing chip uses HE9073 from Hull Semiconductor. The chip is packaged in SOT23-3 and is easy to weld. At the same time, the peripheral circuit is simple and only needs to add filter capacitors to the input and output ends. The output current is large, reaching 500mA. The typical application circuit is shown in the figure below:

The voltage inverter uses TI's TPS60403, with a fixed operating frequency of 250KHz and an output current of up to 60mA. The package is SOT23-5, which is convenient for welding and debugging. The input voltage range is large, 1.6~5.5V, covering most commonly used voltage values. For peripheral circuit ordering, you only need to add three 1uF capacitors to build a complete DC/DC charge pump inverter. The typical application circuit is shown in the figure below:

The complete schematic and gerber files are in the attachment.

4.4 Debugging steps

First make sure that the power supply part is working properly. When the power is not on, measure whether the positive and negative poles of the 5V input are short-circuited, whether the positive and negative poles of the lithium battery interface are short-circuited, whether the positive and negative poles of the 3V power supply are short-circuited, and whether the positive and negative poles of the -3V power supply are short-circuited.

When the lithium battery is not welded, connect the 5V charging voltage and measure the voltage of the lithium battery interface to be about 4.2V. The voltage stabilizing chip outputs +3V voltage, and the voltage inverter outputs -3V voltage. Make sure there is no problem with the power supply, then test the ECG part.

Input a 2mV, 20Hz, 0V offset sine signal through the signal generator, as shown in the figure below:

Probe the waveform at the output of the amplifier with an oscilloscope. If there is no problem with the circuit, the peak-to-peak value of the output waveform voltage is about 1.6V, the frequency is 20Hz, and the offset voltage is 0V. Test the output end of the ECG again. The output waveform is consistent with the output waveform of the amplifier. After passing through the adder, the waveform is offset by +1V. The two output waveforms are shown in the figure below:

Then set the frequency to 50Hz, the frequency of the amplifier output waveform also becomes 50Hz, and other parameters remain unchanged. As shown below:

      Test the amplifier output and the ECG output again. It can be seen from the waveform of the oscilloscope that the output of the amplifier is amplified 1000 times to 2.11V. After passing through the filter, the voltage amplitude attenuates to 330mV, achieving the suppression effect on 50Hz power frequency interference. The waveform diagram is shown below:

After testing with the signal generator, there is basically no problem with the circuit. Then see the waveform by actually measuring the ECG. Place the dry ECG electrode on your chest, as shown in the picture below:

You can see the ECG waveform and the ECG waveform offset by the adder. The waveform is good, as shown in the figure below:

In ECG detection, the impact of power frequency interference is relatively large. We zoom in on the waveform and take a look at the 50Hz power frequency interference. It can be seen that there is almost no 50Hz power frequency interference, and the filtering effect is quite good. As shown below:

After the ECG part is debugged, debug the BLE part.

The BLE part is mainly the development of firmware code. In addition to BLE data transmission and reception, it is also the development of ADC peripheral drivers. Simultaneously collect 3 ADCs with a sampling rate of 250Hz, which are battery power, ECG signal, and base reference voltage.

The above test and waveform parts can be seen in the video.

Note: It is recommended to use Lichuang EDA . If you choose other EDA tools, please upload schematics in PDF format, PCB drawings in PDF format, and PCB files in Gerber format in the attachments. Here you can explain in detail your project implementation principles and mechanisms, precautions, debugging methods, testing methods, etc. It is recommended to introduce your ideas to others in the form of pictures and texts.

*5. Software part

5.1 Host computer

The host computer is used to receive ECG, battery power and other data, and process and display them. The overall software block diagram is shown below:

The host computer is developed based on the visual programming software Labview of NI Engineering. The software is easy to use and can directly call the controls. It greatly shortens the development cycle and is very suitable for DEMO verification and development. LabVIEW (Laboratory Virtual instrument Engineering Workbench) is a graphical programming language development environment. It is widely accepted by industry, academia and research laboratories as a standard data acquisition and instrument control software. LabVIEW integrates all functions for communicating with hardware and data acquisition cards that meet GPIB, VXI, RS-232 and RS-485 protocols. It also has built-in library functions that facilitate the application of TCP/IP, ActiveX and other software standards. This is a powerful and flexible software. You can use it to easily create your own virtual instruments, and its graphical interface makes the programming and use process lively and interesting. The LabVIEW development environment integrates all the tools engineers and scientists need to quickly build various applications, and is designed to help engineers and scientists solve problems, increase productivity, and continuously innovate.

The final host computer display interface is shown in the figure below:

The host computer source code is in the attachment.

5.2 Firmware code

The development environment of the firmware code is Keil 5 and is developed based on the official SDK routines.

During the development of this project, the program was downloaded through the serial port, and the entire download process was very simple and smooth.

When downloading the code, you need to pull the TM pin high and then reset the chip to enter download mode.

Open the official download software PhyPlusKit, connect to the serial port, set the baud rate to 115200, and load the compiled HEX file.

First click Erase to erase, then click Write to burn the program.

After the program burning is completed, pull the TM pin low and then reset, and the program will run normally.

Note: If your project involves software development, please upload the corresponding project source code in the attachment. Here you can describe in detail your software flow chart, functional module block diagram, explanation or popular science of related algorithms, source code structure, construction and configuration of compilation environment, source code compilation method, program burning method, etc. It is recommended to introduce your ideas to others in the form of pictures and texts.

*6. BOM list

The BOM screenshot is shown in the figure below, and the corresponding BOM file is in the attachment.

Note: BOM list involved in the project. Please upload a screenshot of the BOM at this location. Please upload the list details in PDF format to the attachment. Suggestions include model, brand, name, packaging, procurement channels, usage, etc. The specific content and form should be based on clearly expressing the project composition.

*7. Contest LOGO verification

Please upload a project picture containing the competition logo. The logo will be printed on the PCB in the form of silk screen printing.

Click the zip to download the competition logo! (Contest logo).zip

* 8. Demonstrate your project and record it as a video for uploading

Video requirements: Please shoot horizontally, with a resolution of no less than 1280×720, in Mp4/Mov format, and the size of a single video is limited to 100M;

Video title: Lichuang Electric Competition: {Project Name}-{Video Module Name}; such as Lichuang Electric Competition: "Autonomous Driving" - Team Introduction.

More details: https://diy.szlcsc.com/posts/06c94d90c2c447dfbd9ed7339ff4a5b1