I am that type of person who burns really, really quickly when I am out in the sun. I try to remember put on sunscreen, but I do not know when how often I should do that.
When I saw a tutorial from Adafruit on how to build a sunscreen reminder hat, I knew what my next electronics project for the next summer would be.
The tutorial recommends using Adafruit's Flora microcontroller in the sunhat. Although Flora is great for larger wearables (pieces of clothing or large accessories), I found the size of Flora too big for this hat project. In the original tutorial's photos (e.g. this one), the Flora is partly hidden behind the hat's ribbon, but it bothers me that I and everybody else can see it peeking there.
Immediately I was wondering if I'd be able to use another, smaller microcontroller to make this hat. But as it happens, the author of the tutorial must have had a similar thoughts, because she had written "The UV sensor does not work with Gemma or Trinket, so a Flora is required". However, this tutorial was published in 2014, when Adafruit had their older version of Gemma (v2).
I started to research if it was possible to use the newer version of Gemma (M0) to make this hat, because Gemma m0 had many upgrades and is more powerful than Gemma's previous versions.
I live in Northern Europe, and we are thought already in primary school, that near the Arctic circle (and the Antarctic circle), the ozone layer is thinner than elsewhere in the world. Since ozone layer absorbs UV radiation, it acts as a shield that protects against UV radiation. To us who live near the poles of this Earth, this means that we need to protect ourselves from the sun, even if the temperature isn't very high in these areas.
When I noticed that the original tutorial uses Si1145 Light Sensor, that just measures the amount of light and then approximates the UV index based on the amount of light, I was instantly curious about if this approximation has been calibrated to work also in places that are nearer to the poles and have a higher amount of UV radiation than the rest of the world.
I haven't yet bought a true UV sensor (as Adafruit has discontinued those sensors), but I plant to do this some time in the future. I want to get a true UV sensor, that uses I2C, and I want to daisy chain the sensors together, and compare their readings.
I noticed also, that the tutorial code calculates the need for more sunscreen quite simply - if the sensed/measured UV index above a certain threshold and a certain time limit has been passed, then the hat chimes and it is time to put on sunscreen.
I had noticed earlier that if I put on sunscreen when my friends put on sunscreen, some of us would get burns, but the others wouldn't. So I guessed that the type of a person's skin affects the time they can spend in the sun.
Also, since the whole idea of the reminder hat is to remember to put on sunscreen, and sunscreens have different sun protection factor (SPF), that affects how many times more a person can stay in the sun without burning. Simply put, if I can stay in the sun for 15 minutes without burning, with a sunscreen with SPF 30, this means that I can stay in the sun for 30 * 15min = 450min without burning.
The modified code can be found in sunhat_code.ino file.
The code has the skin type 1 as a default. The code has a SPF 50 as a default.