Due to the COVID-19 pandemic, the field of Internet of Medical Things (IoMT), which combines Internet of Things (IoT) technologies and medical devices, has recently received significant development. The paper provides an overview of some successful IoMT projects implemented in recent years, including solutions related to the functioning of the human respiratory system. One of the difficult issues facing medicine now is the rehabilitation of patients who have suffered from COVID-19, and in particular, those who have problems with the respiratory system. The project “Development of a software and hardware complex for monitoring and correcting respiratory functions based on multimodule technologies” is aimed at developing a modern breathing simulator with the ability to monitor the patient's body parameters and use the obtained data to further improve the rehabilitation process. This work discusses in detail the development of an electronic circuit for the breathing simulator of this project.
IoT is currently one of the most relevant and rapidly developing areas. IoT occupies a special
position in medicine, and the special term “IoMT” (Internet of Medical Things) is even used to
refer to IoT in healthcare, meaning the combination of IoT technologies and medical devices [
Moreover, the combination of such areas as IoT and artificial intelligence provides the most
effective solutions. The authors of the study [
One of the most important medical tasks at the moment is the rehabilitation of patients who have suffered from COVID-19, in particular people with problems with the respiratory system. The use of IoT technologies to solve such a problem can improve the rehabilitation process of such patients and achieve more effective results. As part of the project "Development of a software and hardware complex for monitoring and correcting respiratory functions based on multimodule technologies", which is presented in this work, the breathing simulator with realtime monitoring of the patient's body parameters and wireless transmission of the received information to the doctor's device to control the training process is being developed. This paper reveals the process of developing an electronic circuit for the breathing simulator of this project.
This section presents the first version of the electronic circuit and printed circuit board for the
project “Development of a software and hardware complex for monitoring and correcting
respiratory functions based on multimodule technologies” and describes its constituent elements
in detail. The main element of the developed circuit is Raspberry PI Zero. According to studies [
The printed circuit board (PCB) of the " Development of a software and hardware complex for monitoring and correcting respiratory functions based on multimodule technologies" project utilizes a single-board computer Raspberry Pi Zero, as its main component. This Raspberry Pi Zero serves as the central element and controls the entire circuit. Therefore, this board performs the following functions: • Reading data from sensors; • Controlling servo drives; • Executing algorithms for smooth servo control based on sensor data.
The Raspberry Pi Zero was selected for this project for the following reasons [
In Figure 1, the complete specifications of the Raspberry Pi Zero are presented [
However, despite the advantages, one drawback of the Raspberry Pi Zero is the absence of analog input ports. This limitation restricts its usability. In this situation, an analog-to-digital converter (ADC) can be used. In this project, the MCP3008 will serve as the ADC converter, described in more detail in section 2.2.
Additionally, the output voltage of the Raspberry Pi Zero ports is insufficient to control servo drives effectively. To address this voltage issue, transistors 2n7000 will be used in this project to facilitate control over linear servo drives. These transistors are described in more detail in section 2.4.
2.2. MCP3008
The MCP3008 is a 10-bit Analog-to-Digital Converter (ADC) with 8 input channels. It features
low power consumption and a sampling speed of 200,000 samples per second. The MCP3008 is
available in 16-pin PDIP and SOIC packages. A representation of the MCP3008 is in Figure 2(a)
[
For proper operation with the Raspberry Pi Zero, the SPI (Serial Peripheral Interface) interface
will be used to interface with the MCP3008 ADC, which will be discussed in the next section.
Figure 2(b) illustrates the ports of the MCP3008 [
As mentioned earlier, the MCP3008 has 8 channels (CH0-CH7). Additionally, in Figure 2(b), AGND and DGND represent the analog and digital ground, respectively. Vdd is the power supply, Vref is the reference voltage, and CLK, Dout, Din, SC/SHDN will be used for SPI connectivity.
2.3. SPI
SPI (Serial Peripheral Interface) is an interface that follows a standard for serial and synchronous data transmission. Its primary characteristic is communication between one master device and one or more slave devices. In this project, the master device is the Raspberry Pi Zero, and the slave device is the MCP3008. This data transmission involves the use of 4 pins, and their information is provided in Table 1.
sending data and from whom it is receiving.
For the implementation of this project, high reliability and high-speed data transmission are required. For these reasons, the decision was made to use the SPI interface. The connection scheme is presented in section 2.6.
An important aspect of the electronic circuit is the correct control of the servo drives. Linear servo drives will be used in the project to achieve the set objectives. However, they operate at a voltage of 3.7V, which the Raspberry Pi Zero cannot provide. In such cases, it is necessary to use transistors. Field-effect transistors will be used in this project, as they offer the following advantages: • High DC input resistance at high frequency; • High speed of operation; • High-temperature stability; • Low noise level; • Low power consumption.
a) b) Figure 3: Field-effect transistor design (a) and transistor 2n7000 (b)
Field-effect (unipolar) transistors have three terminals: source, drain, and gate. The gate serves as the control pin. Figure 3(a) illustrates the structure of a transistor.
To control the voltage sufficient for operating a linear servo drive, a transistor with a control voltage of 3.3V is required. The 2n7000 transistor, as depicted in Figure 3(b), is suitable for this purpose.
As shown in Figure 4, the block diagram will operate as follows: 1. Power is supplied to the DC-DC converter to ensure that the output voltage remains constant over time. 2. The voltage from the DC-DC converter powers the Raspberry Pi Zero. 3. Raspberry Pi Zero initiates communication with the MCP3008 through the SPI interface. 4. Data from the sensors will be acquired by Raspberry Pi Zero, and based on this data, the field-effect transistors will be controlled.
The entire system will be highly dependent on the algorithms used for controlling the servo drives, as well as the sensors themselves. Ultimately, a feedback system has been developed, which passes through the sensors, creating a closed-loop control system.
In this section, a schematic diagram is presented, divided into blocks for ease of understanding.
In Figure 5, which was created with Altium Designer software, a block of the schematic diagram with Raspberry Pi Zero is presented, where: • CON is the connector, a component that connects external wires to the circuit (double (CON2X1) and triple (CON3X1) connectors are used in the project); • Raspberry Pi Zero is a graphical representation of the Raspberry Pi Zero; • DCDC is the DC-DC converter; • GND is the common ground for the entire circuit; • +3.3V is the power supply for the circuit.
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As mentioned earlier, the SPI interface is used to communicate with MCP3008, so the following Raspberry Pi Zero pins are used in the circuit, as presented in Table 2.
To control the servo drives, the ports described in Table 3 are used.
In the block presented in Figure 6, connectors CON3X1 and MCP3008 are used. The use of triple connectors is necessary to supply power to the sensors while also providing a common ground for them and a contact for transmitting sensor values.
In the schematic presented in Figure 7, the following components are used: • RES – resistor; • 2n7000 - field-effect transistor; • VCC - power supply.
Resistors R3, R2, R1, R4 are used as a load. Resistors R5, R6, R7, R8 are used to limit the charge current of the gate capacitance to prevent the transistor from burning out.
After preparing the schematic diagram, the circuit was assembled on a board. Here, the first version of the circuit is presented, and changes are planned for the future. Therefore, this version of the circuit is designed on a DIP package and a single-sided PCB. The printed circuit board after layout is shown in Figure 8.
The next step involved transferring the image onto the PCB. To do this, the first step was to print the image on special PCB etching paper, as shown in Figure 9(a).
The second step involved using heating elements to transfer the image onto the PCB. This technology is known as laser ironing (LIT). As a result of the heat transfer, the PCB was obtained, as shown in Figure 9(b).
The next step is to obtain the printed circuit board through the etching process. Etching is one of the methods used to remove unwanted copper areas from the PCB as they do not match the PCB's design.
As a result of the steps described above, the printed circuit board was obtained, as shown in Figure 10.
Thus, this paper describes the process of creating the electronic circuit and printed circuit board for the breathing simulator and characterizes its components. During the development of this printed circuit board LIT technology, etching of the printed circuit board and drilling were used. During the development of the electronic circuit, the Altium Designer program was used. The tools of this program allowed to draw a schematic, as well as to develop a circuit for the circuit board. As a result, the first version of the printed circuit board, where the main goal was to work out the program algorithms, was received. Further plans for the project include improving the presented circuit and adding sensors that will be used to measure the patient’s body parameters in the process of training.
This research is funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP19680049).