Intro
If we are to believe the government, one has to be vigilant for terrorist attacks always and everywhere. Commercials, advertisment, no method is shunned to make sure everyone is at their toes all the time. Most countries even have some kind of 'terror meter' which indicates how panicked we should all be. All nice and well, but there's a better place for such indicators: The toilet.
I wasn't the only one who came up with this idea: I have to admit I 'borrowed' it from the second episode of the 'Sam and Max' adventure series. The terror indicator in there has three colors: green for 'all safe', orange for a 'number one' and red for a 'number two'. I liked the layout, so I decided to copy it. So, three levels of terror it was.
How can the air quality in the toilet be determined reliably? Smell detectors do exist, but they aren't cheap and very difficult to obtain, especially for the average hobbyist. We therefore need to acquire this information in a different way. A light sensor turns out to be quite suitable: Assuming that people turn off the light after their visit to the toilet, it should be possible to make a good estimate of the smell level from the time that the light has been switched on. A time-out can be incorporated to deal with those cases when people forget to switch off the light.
Ok, so now we have a way of displaying the smell level, and a way of measuring it. Now, how to combine the two?
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