UV-C Disinfecting Box — Basic Version Tutorial

By Steven Feng, Shahril Ibrahim, and Sunny Sharma, April 6th, 2020

Special thanks to Cheryl for giving valuable feedbacks

For the google doc version of this instruction, please see https://docs.google.com/document/d/1My3Jf1Ugp5K4MV...

Warning

UV-C lights used in this project can be dangerous, please take proper precautions as recommended in the precaution part of this tutorial when building this project. Please note, keep this away from kids and pets, as they may be hurt by accidental UV exposure. Furthermore, UV light could degrade plastic and other materials over time, so it is recommended to check for functionality of the product monthly by putting a camera inside the container to see if the UV lights turn on according to the expected behaviors

Purpose of the project

In this project, we will build a disinfecting container using UV-C bulbs to disinfect personal devices, such as phones, wallets and more. This is especially useful in the current COVID 19 pandemic as the risk of contracting the virus is increasingly getting higher and thus it is important to regularly, and routinely disinfect your personal products such as your phone, wallet, keys and more in a sustainable manner, since cleaning supply and alcohol pads are in low supply.

We hope to be able to create a sustainable solution to regularly disinfect these small personal products in a simple tutorial using common household items and materials that can be easily found online and most hardware stores. We hope to have this almost as a part of your furniture by design, putting it by the front door of your house and allow you to naturally put these items into the box for disinfecting, as you walk in, and then picking them up 15 minutes later.

Background Information
UV-C light is a subset of UV light, with a wavelength of approximately 254 nanometers. UV-C lights don’t exist naturally and are germicidal since germs don’t have a natural resistance to it. This is particularly useful during the COVID-19 pandemic because coronavirus can live on surfaces for up to 72 hours [1]. Thus, as a result, you can easily re-contaminate your hands by touching these personal devices that may have traces of coronavirus and get infected despite frequently washing your hands. According to a research paper by Meecahn and Wilson, 2006 [2], UV-C bulbs takes about 12.5 minutes for it to be germicidal, so for extra safety precaution, we will up the timer to 15 minutes (900 seconds).

To make sure all surfaces of the item we wish to disinfect are disinfected properly, we will use aluminum foil panels to scatter lights evenly around all surfaces of the box. Furthermore, we will be using a net to suspend the object we wish to disinfect so the back sides can also be disinfected properly.

Source:

[1] The Guardian (2020), How long does coronavirus live on different surfaces. Retrieved from: https://www.theguardian.com/us-news/2020/apr/04/ho...

[2] P. J. Meechan, et al (2006) Use of Ultraviolet Lights in Biological Safety Cabinets: A Contrarian View. Retrieved from https://www.ehs.ucsb.edu/files/docs/bs/Meechan_and...

Difficulties:

I have broken up the project into 2 levels of difficulty, basic and advanced (based on your technical skills).

Basic will have the core features but fewer hardware requirements and is easier to construct. It uses a switch from bulb holders to control the lamp, with no additional safety features. Advanced has additional safety features to only allow the light to turn on when the box is closed, detects objects in the box with onboard sensors.

Basic: Only requires 2 bulbs, holders, cardboard, net, and aluminum, no programming nor electrical experience required.

Advanced: Arduino, switch sensor, ultrasonic sensor, etc. basic programming and electrical experience required.

Switch sensor is used to detect open or closure of the box
Ultrasonic sensor to detect objects in the box
Arduino as a microcontroller to orchestrate the switch sensor, ultrasonic sensor, and give an indication of status through 2 LED lights on the outside of the box

Note: In this tutorial, we will be covering the basic level of difficulty, please check out my other tutorial for the advanced variant if you are familiar with hardware or interested to learn :)

Link to advanced tutorial: https://www.instructables.com/id/UV-C-Disinfecting...

Step 1: Usage

Usage:

Plugin the box
Put the items to be disinfected in the box, ensure that the lid is closed and there is no gap anywhere to let the UV lights leak
Turn on the light bulb manually by turning on the switch
Wait 15 minutes, and turn off the UV-C light using the switch
Take out the item
WARNING: Do not reach into the box or open the box when the UV light is on

Step 2: Disclaimer and Precautions

Disclaimer

For UV Light Safety, PLEASE read the UV Safety information provided first below before starting this project: https://www2.lbl.gov/ehs/safety/nir/assets/docs/u...

Health Precaution:

According to Meechan, 2006 [2], UVC lights are not normally found in nature, and it is extremely dangerous to humans. Avoid direct exposure to the bulb and never look directly into the bulb as UVC light can cause severe burns to your skin and retina and may possibly cause cancer
1. I would recommend purchasing a UV-C resistant face shield, and gloves for extra safety protection, similar to this one: https://www.fishersci.com/shop/products/uvp-uv-bl...
2. Check your local suppliers first, as they are often cheaper with faster shipping time.
In this project, you will be working with 110 V Alternating Current, which could be lethal. Be very careful when working on the project, and never do work on live wires. Aluminum foil in the project is also conductive, be careful and don’t get electrocuted by live wires touching the aluminum foil
1. Some precautions you can take include:
  1. Never work on the project when and any component is connected to electricity
  2. For exposed electrical joints, make sure they do not come in contact with aluminum foil or other electrical joints. You can also consider building enclosures for these exposed joints using cardboard
Plastic and many other materials will regard under constant UV exposure, so please reinspect the box for functionality with regular light bulbs or a camera inside the box to make sure the container is functioning properly

Step 3: License

This project is licensed under the Creative Commons Attribution License, which means you can:

Share — copy and redistribute the material in any medium or format

Adapt — remix, transform, and build upon the material for any purpose, even commercially.

Under the following terms:

Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original.

No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.

Step 4: Bill of Material - Basic

Components

Below is the shopping list I created when I build the Disinfecting Box

https://docs.google.com/spreadsheets/d/1TzIsX05gGP...

E17 Bulb to wire adapter

Alternatively, you can use a plug to a different size bulb and then use an adapter, or soldering directly

Aluminum Foil

For maximum reflection. Alternatively, mirrors or anything reflective would also work
Storage Container See suggestion of storage container below

Netting

A way to keep the object suspended to radiate the backside. I used a laundry bag for this purpose. Alternatively, you can use plastic netting that holds fruits, or any fabric with lots of holes in it

UVC Bulb

Pick a UV-C bulb with a wavelength around 254nm, as UV-A and UV-B bulbs (such as black lights) are NOT germicidal
Ideally, you should try to find a standardized bulb (E26, E27), if not, you can use an E17 bulb and adapter or replacement bulb and solder the + side (bottom of the bulb) and - side (sides of the bulb) to the ground wire. Only do this if you are an experienced electrician.
The number of bulbs required depends on the size of the box and the Wattage of the bulb. There is no definite answer. Usually, 2 bulbs, about 3W each or 1 bulb around 10W would be sufficient for a 30cm x 20cm x 20cm box

Cardboard

Foam board would also work, these act as support within the box

Storage Container

The box can be made out of any material and the size largely depends on your need.
You can use a banker’s box, a shoebox. In my case, I found a storage box on amazon. Size is dependent on how many devices you want to store on it.
I would suggest at least 30cm x 20cm x 20cm. Size of UV-C light bulbs and adapter may vary, make sure you read rest of the instruction first, and reserve enough space for the bulbs

Tools
Soldering Kit (Optional)

if you don't want to solder, please use male to male and male to female jumper wires instead

Hot glue gun

You can also use double-sided tape or glue alternatively

Cutting Tool

You can use an exact knife, scissors, or tin snips based on availability

Drill

I used an electric drill with 5mm drill bit for the LED, you can also use cutting tools to cut holes out on the storage box

Sewing kit

For the net, alternatively, you can also just use glue or tape

Step 5: Building Aluminum Side Panels

The purpose of the Aluminum is to add another layer of protection to prevent UV lights from leaking, and to add reflectivity of the UV-C light so all sides get exposed to the UV-C rays evenly

1. Measure inside dimension of the container of choice, and make cardboard cutouts of it
2. Glue a layer of aluminum foil over these cardboard cutouts to maximize reflection and allow the UV lights to distribute evenly

Remember to put aluminum foil in the inner side of the lid

Note: according to research done by Pozzobon, V., et al (2020), the bright side of the aluminum foil offers better specular reflection, while the matte side offers a better-defused reflection. (See Picture 3). This means if you want the light to scatter evenly throughout the box, use the matte side of the aluminum on the panel. If you want concentrated aluminum lights in a certain part of the box, with a few relatively darker spots, then I would recommend using the bright side of the aluminum foil.

Pozzobon, V., et al (2020) Household aluminum foil matte and bright side reflectivity measurements: Application to a photobioreactor light concentrator design. Retrieved on April 13, 2020, from https://www.sciencedirect.com/science/article/pii/...

Step 6: Cutting Holes

On one of the corners, carefully make a cutout that is large enough (about 2cm x 3 cm) for a single plug to go through, this is for wires to pass through in the future. One tool that I found really effective at cutting thick cardboard is tin-snip. But you can use an Exacto knife or scissors too.

Note: In the image below, I taped the size of the cutout to give it extra strength so the box doesn't fray

Drill small holes along the sides of the box for better ventilation and heat dissipation

Step 7: Initial Testing - Expected Behavior

Screw conventional light bulbs into the light socket, use the switch provided on the light socket to turn it on, and off, to make sure the light socket adapter is functional

Step 8: Building UV-C Bulb Shield

The purpose of the UV-C Bulb Shield is to block lights from the bulb from shining directly up (into your eyes when you accidentally open the box) and redirect light downward where the object you are trying to disinfect is. Refer to 2nd and third picture as installation reference
Cut out two pieces of cardboard to make 2 light bulb reflectors, with the width about 8cm and length about 3.5 times the diameter of the UV-C bulb of choice.
Fold it into a right triangle on the longer edge, and curve the hypotenuse of the right triangle by pressing on the surface
1. This will make it easier to install the light adapters for the UVC bulbs because it will better fit the size of the bulb
Put aluminum foil also along the hypotenuse side. This is the bulb reflector, which is also responsible for redirecting UV lights downward and blocking the UV light from shining and directly harming the user’s eyes if the fail-safes failed.
Note: Fail safes include the switch sensors and ultrasonic sensors that will turn off the UVC lights automatically when the box is opened

Step 9: Build the Suspension Net

I used a laundry bag for the net, ideally, you just need a piece of fabric that is translucent, and can be see-through by the ultrasonic sensor. Some examples of these materials include fruit bags (Refer to 4th image for this step), laundry bags, window screens, etc.

Fold the sides of the net in, and sew the sides in place, so the edges are firm on the edges. This will make this step much easier (Refer to 1st image for this step)
1. You can also consider gluing the sides in, but it won’t look as nice as sewing
Build a frame for the net so you don’t have to glue it directly onto the aluminum walls, and hopefully, this will make the repair easier. You can build this frame either from scratch using cardboard, or use the box you find from dozen of canned drinks, hollow the inside out. (Refer to 2nd image for this step)
Spread the net along the side, glue it in place, make sure the net is tight (Refer to 3rd image for this step)

Step 10: Finishing Up...

Glue light reflector that we built earlier in place, put UV bulbs in the light socket adapter, and tape (or glue) it onto the reflector. (Refer to 1st image for this step)

Tape UV Hazard sign on the top of your box, because you do not want your guests to accidentally open this box when the UV light is still on. Keep this item away from kids and pets, and congratulations, you are done!

Stay Safe, and wish you the best of luck!

If you want additional safety switches, check out the advance tutorial