The new coronavirus has been ravaging the world for several years, and we are now used to disinfecting with alcohol-based sanitizers and sprays, but how do we disinfect our goggles, keys, mobile phones, watches, banknotes, laptops and other items? Especially express packages, the virus survives for a long time on such packages, and flows from high-risk areas to other areas, causing hidden dangers of transmission and greatly increasing the difficulty of epidemic prevention. A convenient solution for sterilizing such items is Ultraviolet (UV), an ultraviolet (UV) sterilization box that you can make yourself.
Ultraviolet light is light with wavelengths from 10 to 400nm. It has a shorter wavelength than visible light but longer than X-rays. Broad UV radiation falls into three broad categories:
· UV-A with wavelengths from 315 to 400nm
· UV-B with wavelengths from 280 to 315nm
· UV-C with wavelengths from 100 to 280nm
UV-C sterilization is a method of killing pathogens, viruses and bacteria. UV-C damages the DNA of pathogens, impairing their vital cellular functions. The effectiveness of this germicidal method depends on the duration of exposure and the intensity and wavelength of UV radiation. Therefore, try to get enough UV-C to irradiate the whole of the object being sterilized.
The germicidal lamp mainly has a UVC mercury lamp tube as the light source, which emits light of 253.7nm. UV-C LEDs that produce light with wavelengths between 255 and 280 nm can also be used. In this project, we used two 11 watt germicidal UV tubes.
The features of this sterilizer are:
254nm wavelength has effective germicidal effect
· Closed UV leak proof box
· Reflective surfaces maximize reflectivity and provide effective 360-degree coverage
· Magnetic retention of door/lid to keep it securely closed
· Exposure time can be set from 1 to 10 minutes by rotary switch
· Pause the timer if desired
· Simple operation with start/resume and stop/pause buttons
· Display showing remaining time and alarm messages
· If the door/lid of the box is opened, the safety feature of the UV light is turned off
Construct
UV-C rays are harmful to the human body, so please use a suitable protective shield. This project was built using an empty printer cartridge as shown.
Front opening of UV disinfection cabinet
Stick aluminum foil on all the inside of the box to scatter the UV rays inside the box. The outside of the box can also be covered with kraft paper. Use cable ties to mount two 11W UV lamps on the top plate of the box.
circuit and work
The control core uses an Arduino, a small footprint Arduino Pro can be used, but any Arduino variant can be used. The circuit diagram of the UV disinfection box is shown in the following figure.
It includes a TM1637 module, 5V DC power module (Module1), Arduino Nano (Board1), 5V single changeover relay (RL1), a rotary switch, a magnetic gate switch, two 230V AC UV tubes and some other components.
A rotary switch looks like an analog potentiometer, but it is a digital device that rotates in a loop without any endpoints, and is used to set the time. It does not give any specific value and can be interpreted as giving the direction of motion. The most common rotary encoder is the scroll wheel on a computer mouse. Just like a mouse, a rotary encoder can be rotated and clicked (pressed). In this circuit, its built-in pressure switch is not used. Inside the encoder there is a slot plate connected to the common ground pin C, and two contact pins A and B, as shown in the figure below.
In addition to these three pins, there are two pins for momentary switches (not used). When the knob is turned clockwise, pin A goes to ground before pin B, and as the knob continues to turn, pin A goes low before pin B. When turning, a click can be felt because of the pawl (stop). There are 20 of these pawls in a full circle.
Similarly, when the knob is turned counterclockwise, the pulse train will go high with pin B first, followed by pin A. The pulse sequence is shown in the figure below.
The encoder used here has five pins as shown in the image below. The encoder's pin DT is connected to the Arduino's pin 2, while the CLK pin is connected to the Arduino's pin D3. The + and GND pins of the encoder are connected to the 5V and GND pins of the Arduino, respectively.
software design
Through software monitoring, when the A pin changes from high to low, the level of the B pin is detected to determine the rotation direction. For example, when B=1, it is clockwise, and when B=0, it is counterclockwise.
Set a variable with an initial value of 0, which records the number of pulses, that is, the value of the pulses generated by rotation. Since the encoder is mechanical, there is a lot of bounce when the rotational position changes and needs to be debounced in software.
The above encoder tasks are all handled by the NewEncoder library. The encoder's pins A and B must be connected to the Arduino's interrupt pins because the library uses interrupts to track rotation. The Arduino Uno, Nano or Pro versions have only two hardware interrupt pins, pins 2 and 3. The encoder will not work if connected to other digital input pins.
A 4-digit 7-segment display is used to show the time. A TM1637 IC based display module is used which only needs two pins on the Arduino to display numbers. The clock pin of this module is connected to Arduino pin 4 and the data pin is connected to pin 5.
This module uses the TM1637 library from Avishay Orpaz. You can use the Arduino IDE's "Project - Load Libraries - Manage Libraries" option to search and install this library.
Two momentary push switches (S1 and S2) act as start and stop buttons. One pin of the start button is connected to pin 6, while the second pin is connected to ground. Likewise, the stop button is connected to pin 7 of the Arduino.
Button presses are handled by Matthias Hertel's OneButton library. It can also be installed using the IDE's "Project - Load Libraries - Manage Libraries" option.
As shown in the picture above, the magnetic door sensor switch is fixed to the upper edge of the door.
The magnet part is attached to the door, while the reed switch part is attached to the box. The reed switches are connected to pins D12 and GND of the Arduino, respectively. The mode of pin D12 is set to INPUT_PULLUP to activate the internal pull-up resistor on pin D12.
A 5V buzzer is connected to pin D11 of the Arduino to signal an alarm.
As shown, the circuit is placed inside this cover, with the front serving as the control panel.
A 5V relay is connected to pin D10 of the Arduino through a 2N2222 NPN transistor with the base connected to the 18k resistor to limit the base current. The relay will be on as long as the D12 pin is held high. Off-the-shelf relay modules can also be used in place of relays and transistors. However, if the relay module is turned on using a low level, appropriate changes need to be made in software.
The NO terminal of the relay is connected to the UV ballast, which turns on the UV lamp when the relay is conducting. When the UV light is on, the indicator LED connected to pin D13 of the Arduino will light up.
The following is the working status digital tube of the disinfection box:
Use a UV sterilizer
The disinfection process depends on the duration and intensity of UV exposure. Small items like keys should be exposed for at least two to three minutes, while larger items should be exposed proportionally longer. Use a small steel frame to place the items in the box so the UV rays can also reach the lower part of the item.
First put the items to be sterilized on the steel frame and close the door. When the door is open, the display will show "door". When the door is closed, the display will change to "00:00". Now you can use the rotary switch to set the time. It can be set any time from 1:00 to 10:00 If the time is at the maximum or minimum value and continue to rotate the encoder, the buzzer will make a "beep" sound.
Now press the start switch. The relay will turn on and the timer will start counting down. The remaining time appears on the display. When the countdown is complete, "end" will be displayed and a long "beep" will be heard. Now you can open the door and take out items.
When the door is closed, the time period will automatically be set to the last setting. The rotary switch can be used to make changes if needed, or more items can be sanitized using the old time setting. Shade can interfere with disinfection, so don't store too many items at once to avoid shade.
If the stop button is pressed during the countdown, the display will show "stop". After pressing the Start button, the countdown will resume and complete as usual. However, if the door is opened during the disinfection process, the process will be canceled, and when the door is closed, the last time set is restored. As soon as the door is opened, the UV lamps are turned off and the disinfection process is stopped. While setting the time, it can be reset to "00:00" by pressing the "Stop" button.
PCB
Warning: UV-C rays are harmful to humans. Do not directly expose yourself or others to UV light.