how to make a variable light dimmer circuit without potentiometer?
Answering this question as I myself was searching for an answer like this a long time ago.

One possible way is to have:


Zero crossing circuit - I prefer this one:
https://www.avrfreaks.net/forum/zero-crossing-detector-using-4n35-optocoupler
Triac driver optocoupler without zero-crossing detection. MOC3021M is an example of one
Other stuff like triac itself with correct snubbing, power supplies, etc


However, It should be noted, though this project is pretty simple and straightforward - it involves mains AND touch sensor at same time. While it is easy to isolate everything with only two optocouplers, It is also true for an opposite. If there is not enough precaution in mains isolation - a strong shock would be the least awful outcome.  I would not recommend doing it unless you know what are you doing for sure. 

Just buy one - it will be an easier, safer option. And no one will die. Probably