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Disinfecting PPE masks using dry heat and Arduino temperature controller

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profdc9:
PPE masks can be disinfected using dry heat, usually in the range of 60C-90C and 20-90 minutes.  I am designing a cabinet including temperature controller for this purpose.

The heater is a 60 watt incandescent bulb.  I chose this because both the bulb itself and fixtures are readily available.  It is switched on and off by a simple relay to control the temperature.

I am designing a temperature controller based on an Arduino Nano.  This circuit is designed to be built on perf board or even a solderless breadboard if required.  It does not use a LCD to communicate, instead it uses four LEDs which flash codes.  It also has three buttons and a connection for a piezo buzzer or speaker that is an alarm when the disinfection cycle is complete or there is an error.

My question is: is the circuit here simple enough to be built by most hobbyists?  I kept it as simple and with as few components as possible.  It is powered by USB except for the light bulb which is powered directly from mains.

I have included the schematic, the PCB I designed for it (which doesn't have to be used, it's just an example), and the traces for the PCB.  It is laid out as a single sided board so that home board etching techniques can be used to produce it.

Any comments are appreciated.

Whales:
Quick aside: sometimes silicon isn't the best solution if you want things to be simple and accessible.

eBay search terms "temperature control oven":



Pureley mechanical device, turns mains on and off like a switch when a certain temperature is hit.  Attach your bulb directly to it, no other circuitry needed (other than fuse, power switch and power cord).

The 300C models are probably not what you would want.   EDIT: here we go:




profdc9:
Are these able to keep the temperature to within a 2 C or so?  These usually aren't used at the lower end of their range.

https://www.amazon.com/uxcell-Thermostat-Adjustable-Temperature-Controller/dp/B07PFVV6QZ

I suppose they are easy enough to get and try, it's just that the LM35 is accurate to 0.5 C. 

There is also this too...

https://www.amazon.com/Temperature-Controller-Thermostat-Thermometer-Charcoal/dp/B01DTI755W

I have more confidence in that, and it has a timer which is very necessary in this case. I'm not sure that it has 2 C accuracy either being designed for such a wide range.

The thing I'm not sure about is how sensitive the masks are to damage.  It will be harder to get acceptance if the process deviates from what has been tested before.  On the other hand, not having to build a circuit and just plugging in something is very compelling.  The circuit though, can be built so that once set up, you just press the button and it does a cycle.


Whales:
They won't be accurate to within 2C.  Their hysteresis will be larger than that for a start.

Why the 2degC number?  It's extremely difficult to get all of the air within a chamber within that tolerance to begin with (unless you have an internal fan circulating it).  Based off your requirements you have a wide tolerance range (60-90C).

N.B. don't assume the digital options are better or more reliable.  If you want a timer then it may be worth going for a mechanical one too, as the UI it provides is much simpler than any digital option (no manual needed) and it's easier for repairers to understand.

james_s:
Why reinvent the wheel? You can buy a ready made PID temperature controller for around 20 bucks, add a thermocouple and SSR and you are ready to go. Most have an auto-tune feature, add a light bulb or several and dial it in, holding the temperature within +/-1C should be trivial.

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