Ultraviolet-C Against COVID-19

Updated 20210106
This is my small contribution to the fight against the SARS-CoV-2 virus which causes the COVID-19 pandemic.

All viruses and most bacteria and spores are deactivated/killed by far ultraviolet (UV-C) light. Their RNA/DNA absorbs the 260-280nm wavelength and is broken by it. This also works on bacteria resistant to antibiotics like MRSA. Many
medical reports confirm the effectiveness of this type of radiation. It is often used for drinking water treatment and in hospitals.

UVC boxes are available that can disinfect small items quickly, such as medical instruments. The problem is the tubes that generate the light have a short lifespan and are fragile. Some boxes don’t even produce genuine UVC light and are dubious quality. Personally I will be using this unit to treat masks, my ‘phone, keys, and some other small items. We should not forget there are plenty of other pathogens out there besides SARS-CoV-2. These can also be defeated by UVC radiation.

In particular masks can harbour bacteria and disposing of many good quality masks is wasteful. This will make my masks last longer and give some assurance I’m not breathing in long-lived bacteria and viruses like noro-virus (winter vomiting bug) which can live on surfaces for weeks.

*** DISCLAIMERS ***
I MAKE NO COMMITMENT OF EFFICACY OR LACK OF RELATING TO DISINFECTING EFFECTS
UVC RADIATION IS DANGEROUS TO HUMAN EYES AND SKIN. I TAKE NO LIABILITY FOR DAMAGE CAUSED BY MISUSING THIS DESIGN
DO YOUR OWN RESEARCH AND DECIDE IF THIS PROJECT IS FOR YOU!
UV_Hazard
Recently UVC LEDs became available which overcome problems of fragility and short lifespan. I secured a small order of them from
Lite-On Corporation via Mouser. The specification for this project is:
  • A unit approximately 200 x 100mm
  • Safety interlock to prevent exposure of human eyes or skin to UVC radiation
  • Standard and easily available electronic parts, no software
  • Open source hardware
  • Two choices of UVC LED package/footprint, ’3939’ and ’3535’
  • Powered through a standard USB-C connector and power supply
  • Compact, efficient, and reliable
  • Minimised cost
  • Choose your enclosure
The unit is designed in KiCAD open source PCB and schematic capture software. The first prototype had a few footprint issues, but an improved issue B version in KiCAD 6 format is available here with a PDF circuit. Other files on request. Photo of an assembled board:
LED Board Issue B

Charging a phone and sterilising it with the same power adaptor (USB-C) is rather appealing!

The PCB is designed to fit in a hinged lid plastic box, and is 150x50mm. Many types of box can be used such as those with a hinged lid. The prototype is housed in a roughly drilled plastic box, with the magnet screwed in at one corner. Photos follow.
LED box1
LED Box2
Power/timing LEDs face the user, while the UVC LEDs and other parts face into the box. Closing the lid activates a magnetic (Hall effect) sensor and begins timing. Time elapsed is shown on a row of 8 LEDs which turn on every 30s until the green power LED goes off. USB-C supports enough current and avoids difficulty in sourcing power supplies as most phone or laptop chargers can be used. The box only draws power from USB - it is not an active USB device.

While the prototype is a bit rough, the electronics work fine. The timer has a nice row of LEDs and clear indication, implemented without a microcontroller and at low cost. 4 minutes of UVC radiation may not be enough for through disinfecting - the circuit values can be changed to get a longer timing, or simply lift the lid and place on again for another 4 minutes.