Team:NEU CHINA/Hardware
The spread of the SARS-CoV-2 has had a tremendous impact on human activities. One of the main reasons why the spread of the virus is too difficult to control is that it often takes a few days after a person is infected with it before they have apparent symptoms, but in the days without the onset of the disease, carriers will move around freely in various high-traffic places and spread it, Then infected people will spread the virus to more people within a few days without developing the disease. This eventually leads to an outbreak. This characteristic is also found in the transmission of other coronaviruses. Therefore, real-time virus detection is necessary for high-traffic sites, and once the virus is detected in the air of a particular environment, immediate measures will be taken to isolate people who have been or gone there, together with other measures, to reduce the risk of outbreaks.
Our team have designed a hardware that can sample and detect the air in the environment. Once the virus is detected, the sampler will alarm. The device is generally divided into three parts, sampling system, titration system and detection system.
Sampling system
The sampling system is similar to existing ambient air samplers. It uses constant temperature and current sampling. The air sample is absorbed into the absorption bulb and the excess air is discharged through the liner.
Titration system
The general process of titration system is to titrate the solution to be detected in the absorption bulb into 24 wells (up to 96), and different wells can detect different indexes.
Detection system
The liquid in the 24-well culture plate is detected by fluorescence. If the fluorescence signal reaches the threshold , the alarm will be started. The overall detection method is similar to the microplate instrument. The 24-well culture plate will move along a certain trajectory, so that different pass through the light source respectively to achieve the fluorescence detection.
Hardware structure design
Spatially, the hardware equipment is divided into four main parts from top to bottom, including: upper layer - circuit electrical equipment and control box, middle mezzanine - enrichment fluid conduction control and liquid flow titration equipment, middle layer - drop control chute and fluorescence detection device and the lower layer -leakage catch tray.
Upper layer - Circuit electrical equipment and control box (control box)
Since the working space of the main operation box (hereinafter referred to as the operation box) is required to perform the tasks of titration of enrichment solution and fluorescence detection, it will be in a long-time wet space operation. Therefore, in the design of the box structure, the circuit part that controls the hardware operation is assembled in a separate box (hereinafter referred to as the control box) on the upper part of the main box, and the control part such as the control buttons are mounted on the side of the control box. Different color buttons are installed in different holes on the box to display the operation process as described in the circuit introduction.
Intermediate mezzanine - Enrichment fluid conduction control and liquid flow titration equipment (T-box)
At the top plate of the running box, we installed a small T-shaped box (hereinafter referred to as T-box), which holds the inlet interface side of the buret glass tube that is in direct contact with the inside of the running box. The structure of the buret glass tube is designed for a mouthful of liquid inlet and six mouthfuls of liquid outlet; for the drip rate control, we use solenoid valves for automatic control. The enriched liquid in the air sampler is controlled by the flow rate through the solenoid valve, and is connected to the interface side of the glass tube in the middle sandwich with a flexible rubber tube as the transmission medium. The inlet port of the glass tube is encapsulated in the T-box and connected with the flexible rubber tube; the outlet port extends from the six round holes in the flat shoulder of the T-box, which can just correspond to the six holes of the 24-well culture plate underneath it, so as to complete the function of injecting the enrichment solution into different holes in the same row of the 24-well culture plate respectively.
Middle layer - Drop control chute with fluorescent detection device
This part is the main part of the run box to perform its functions. Functionally, the whole can be divided into two parts - the enrichment titration part and the fluorescence detection part. The enrichment titration part is on the side of the box opening the door, and the fluorescence detection part is on the inside side near the back panel of the box, and the two parts are connected by slides and chutes. The motor trays on the left and right sides inside the box raise the notch plate to a preset position and snap the motor into the notch to fix it, and the motor can control the rotation of the gears. The grooves and protrusions on the gears correspond with the protrusions and grooves on the lower side of the 24-well culture plate carrier tray, so that the motor drives the gears to rotate and make the 24-well culture plate carrier tray move back and forth along the slide inside the box. 24-well culture plate carrier tray only plays the role of driving and fixing the 24-well culture plate, and its upper and lower sides do not block the perforated part of the 24-well culture plate.
Lower layer - Leakage catch pan
During enrichment titration, if the liquid spills or splashes outside of the wells, it can lead to the trouble of requiring the operator to repeatedly wipe to clean the residual liquid at the bottom of the chamber and to disinfect it. Therefore, we elevated the entire part of the run function with two elevated plates on the left and right under the inner side of the run box, so that a space of a certain height is retained on the lower side of the 24-well culture plate being titrated. In this space, we placed an appropriately sized catch tray to directly hold the liquid that might spill during the titration or accidentally run out due to operational errors. If there is a lot of liquid in the tray, it can be removed and disposed of in a uniform manner.
The sampling system is similar to the existing ambient air sampler, using constant temperature and constant flow sampling, the air sample is absorbed into the absorption bulb, and the excess air is discharged through the tail pipe. It is worth mentioning that this device adds a virus-killing device to the existing air sampler. The air that does not enter the absorption bulb will pass through the high-temperature treatment box as well as the alcohol bottle and finally be discharged into the air, so that the air passing through this device is purified to a certain extent.
The absorbent solution obtained from the enrichment in the sampling system, through a flexible hose, directly into the enrichment liquid conduction control and liquid flow titration equipment. Enrichment titration part of the work, through the programming method to control the circuit opening and closing cycle and time cycle, so that the back and forth operation of the slide and control the T-box in the glass instrument titration liquid rate, frequency of the solenoid valve these two work to keep alternating. That is: the titration part of each full line of 24-well culture plate after the well (six outlet corresponding to a line of six holes), motor control 24-well culture plate tray to the inside of the box slide a line of 24-well culture plate spacing, at this time the six outlets of the glass tube corresponds to the next line of six empty holes waiting for titration, solenoid valve and then continue to control the flow of liquid from the outlet until the line of six wells full of drops, after the drop full motor control 24-well culture plate bearing After the tray continues to slide inward a line spacing ...... repeatedly so four times, all the holes of the 24-well culture plate are full of enrichment solution; at the same time, the 24-well culture plate tray also along the slide will 24-well culture plate to the inside of the box blue fluorescent plate directly above.
When the 24-well culture plate is directly above the blue fluorescence plate, the fluorescence detection part can start working. When the fluorescence detection section is working, the microscope camera, the 24-well culture plate and the blue fluorescence plate are in order from top to bottom. The blue fluorescence plate switch is turned on at the control box and blue light is transmitted through the 24-well culture plate from the lower side. If the enrichment solution contains the indicator protein - EGFP, they will show strong green fluorescence under the blue light. At this point, we use a microscope camera to capture the imaging so that it is presented on a mobile-ready device such as a computer or phone as a way to see if the enrichment solution in each well has green fluorescence. When the fluorescence detection section starts working, the operator must ensure that the door of the chamber is tightly closed so that the interior of the chamber remains in a dark field of view.
After the fluorescence detection part is finished, press the recovery switch, the motor will drive the 24-well culture plate carrier tray to return to the initial position and wait for the next operation.
Power supply module
Our instrument uses three-pin plug to pull in the voltage. Instruments in the electronic components include stc89c51 with a standard working voltage of 5V, three-color LED lamps, fluorescent board and solenoid valve with the working voltage of 12V etc. During the working process, this instrument transfers the 220V AC voltage into 12V DC power supply by a transformer, and then use the DC-DC step-down voltage regulator power supply module to transfer the 12V DC voltage into 5V DC voltage, and then to obtain the working voltage suitable for all the components inside the instrument.
Control module
In our circuit, stC89C51 is parted as the core control chip.
1. Clock circuit
Crystal oscillator is the core of the clock circuit. It is a kind of electronic component which can produce stable oscillation frequency. Oscillation frequency (whose unit is MHz) is the crystal oscillator’s basic parameter which determines the working frequency of the single chip microcomputer. We choose 12MHz crystal oscillator in our single chip with a clock cycle of 1/12us, and the machine cycle of 12* (1/12) us(which equals to 1us). There are 2 ports in the circuit. Once port XT1 is connected to the 18 pin (XTAL2) and port XT2 is connected to the19 pin (XTAL1), clock signal will be provided to the single chip microcomputer. The crystal oscillator circuit is shown in the figure below.
2. Reset circuit
The reset circuit is used to restart and then initialize the single chip, so that the program can be restarted. When the single chip fails due to program problems, the single chip can reset itself by sending a reset signal to the ninth RST of the reset circuit. The reset circuit is shown in the figure below.
3. In-output circuit
Each I/O port of the MCU can be independently used as input or output. Stc89c51 includes four groups of I/O ports, namely P0, P1, P2 and P3.
In this instrument, we select P1 as the control input, P0 and P2 as the control output, wherein P0 serves as the control output of LED indicator, solenoid valve and fluorescent plate, and P2 serves as the control output of motor drive.
Main operating board module
Arranged on the outside of the instrument, the main operating board is responsible for the input of control signal and output of LED indicator light.
1. Input section
The input part of the main control board is set with a self-locking switch and a no-locking switch, which are input through port P1 of STC89C51. The circuit diagram is shown as follows.
The lock switch acts as the master switch of the instrument. When it is disconnected, the instrument is in an uncontrollable state; while when it is closed, the instrument will turn into a controllable state. The no-lock switch is used as the signal input section for the instrument to start the single work. To explain, when the instrument is in a controllable state while hasn’t started to work, the single pulse signal can be input through no-locking switch to make the instrument start the work.
2. Output section
LED tri-color lights (with the color of yellow, green and red) are set in the output part, which are output through P0 port of STC89C51. The LED yellow light is on when the lock switch is disconnected and when the instrument is in an uncontrollable state; The LED green light is on when the lock switch is closed and when the circuit is in working state; the LED yellow light is on when the lock switch is closed and the circuit is in non-working state.
The relationships between LED indicators and their corresponding states of the device are shown in the following table.
| Corresponding state of the device | LED yellow light | LED green light | LED red light |
| Uncontrollable state | On | Off | Off |
| Controllable and working | Off | On | Off |
| Controllable but non-working | Off | Off | On |
The output module circuit of main operating board is shown in the following figure.
Action module
Step motor 28BYJ4, the main execution element in the modern digital program which can convert the pulse signal into angular displacement signal or linear displacement, is used to drive the movement of the 24-hole plate in the action circuit. The stepper motor can not be directly connected to the industrial frequency AC or DC power supply to work. It can only be started by using a special stepper motor driver, letting the drive unit directly couple with the stepper motor. In our instrument, the stepper motor 28BYJ4 is driven by ULN2003 drive plate, which will receive stc89c51’s output of P2 port. We also use two stepper motors 28BYJ4 to drive the 24-hole plate, which rotate in different directions respectively. The circuit diagram is shown as follows.
Liquid control module
On/off components of the liquid control module use a 12V (working voltage) normally closed plastic solenoid valve, 5V working voltage provided by STC89C51. We use 12V voltage output from the transformer to connect one terminal of the solenoid valve, and port P0 of the MCU to connect another terminal. When port P0 outputs high voltage, Voltage at both ends of the solenoid valve is 7V, which means it cannot reach the working voltage, thus it will be in a closed state; Instead, when the P0 port outputs a low voltage, the voltage at both ends of the solenoid valve is 12V, which will reach the working voltage and thus can go into the working state and realize the control function of the liquid control module. The circuit diagram of the liquid control module is shown in the following figure. (Since there is no solenoid valve in protues, we use LED with working voltage of 12V to replace the solenoid valve)
Fluorescence detection module
The LED blue luminescent plate with a working voltage of 5V is used as the fluorescent detection light source generation element in the fluorescent detection module.
Then the signal will be output through port P0 of stc89c51 in order to control the LED blue luminescent plate. The circuit diagram is shown as follows.
The whole circuit
The whole circuit is shown as follows.
Physical encapsulation
In the circuit part of the instrument which has a concentrated distribution of stc89c51, small electronic components act as the main part of the clock circuit and reset circuit module. The whole circuit is encapsuled with PCB, while the other modules distributed in each part of the instrument are connected using Kf301-2p /3P/4P bit wiring terminals.
The 2D view of the PCB encapsulation is shown in the figure below.
The 3D view of the PCB encapsulation is shown in the figure below.
After designing our entire project, we took into account the practicality of the project. A few months ago, a popular snack in China was tested positive for SARS-CoV-2 which caused panic among the general public, and it was this problem that made us realize that the coronavirus can not only cause diseases threaten our health, at the same time, the unpredictability of its presence in the environment also leads to food safety problems that are closely related to our lives, making it more difficult for humans to fight against coronavirus. Therefore, a hardware that can detect viruses in the environment in real time will help us to prevent viruses effectively.
We visited a pig farm and learned that besides coronavirus, swine fever had also affected them greatly before, resulting in the death of a large number of pigs and heavy losses, while the detection methods used by pig farms were so outdated that they could only infer whether the virus was still present by trying to place healthy pigs in sterilized pens to see whether they would be infected. If we can adapt our hardware to detect more viruses in the future, we will be able to greatly help improve the efficiency of virus detection in the environment.
In order to solve these problems, our team designed a hardware. The whole process of hardware equipment from 3D design and circuit design to fabrication, assembly, debugging, trial run and official operation is all done by our team members. In order to ensure the safety of the self-assembled equipment and stability during debugging, we also set up some very effective parts with fault detection and debugging guarantee functions as well as convenient details for operation in the structure and circuit design, which can be found in the engineering drawings of 3D design and the circuit design diagram section. An identical device can be made according to the information we provide such as drawings and parameters.
In addition, improvements based on our team's hardware not only will hopefully enable real-time monitoring of more coronaviruses, and even more viruses, but also can provide a reference for future environmental virus monitoring. In the end, we will upload the assembly drawings of all parts.
Declaration of Originality
The hardware equipment of NEU_ China team was originally completed by the team members. The process from 3D modeling design, circuit design to fabrication, parts assembly, debugging, trial run, and official operation is all done by the team members themselves. This is hereby stated.