PeterH:
The software side looks non-trivial but definitely feasible. It is the hardware and power side that is uncertain. It's certainly possible to regulate mains voltage AC directly and plenty of resources showing how to achieve this using zero crossing and a triac, but it's not IMO a job for a novice.
I agree with you completely Peter, but when I see advice like this, I hear "Don't cook, leave it up to the chefs!" People learn by doing. Introducing someone to the right concepts points them in the right directions to begin learning. Usually THAT is the step that people are stuck on (just like I was with the PID issue you helped me with.)
I am not saying that you are wrong, I just keep seeing that type of advice here and it is troubling and could easily be perceived as insulting (it would be to me.) I don't consider myself stupid, a newbie, or even a novice simply because I ask a question. Sometimes I just need someone to point in the direction that I need to look to speed up the process of learning, to introduce me to a new concept I wasn't aware of, or to break my tunnel vision. But I know that I will need to go and learn about whatever is new on my own. Just need a nudge sometimes or a fresh perspective.
Personally, I find it much more respectful to approach helping people that way.
There may be cases where we tell someone that a triac is the proper route, and they simply go and plug one in without understanding it, but that is unavaoidable (and hopefully the last time they would try that!) A smart person will instead go and look at how a triac works and all the theory behind it, then either experiment SAFELY or come and ask more questions about parts they don't understand. So, to first assume that they wouldn't go and try to learn about the concept would assume they aren't a smart person.
Everybody is a newbie and a novice at some point. Nobody is born knowing how to connect and control a triac. The best time to learn is when you have something you need to apply it to.
To close off certain information because we assume that someone isn't going to understand it feels a bit arrogant to me. We are here to learn, to teach, and to help, right?
You are always helpful, so please don't think I am assuming that you intend it that way at all. Just would love for people to take a moment and think about how this would come across to them if someone were to say it to them.