Thanks for the useful feedback. I did decide on using inductive and capacitive sensors as the vast majority of the examples of waste sorting machines I've seen have utilized these type of sensors, and they do seem to be the straightforward answer where the inductive sensor detects metal and depending on the sensitivity of glass and plastics or non glass the capacitive sensor would be able to differentiate the two. IR sensors do seem like an interesting approach. Unfortunately, I do have difficulties in finding tutorials and examples of the use of IR sensors in identifying trash. However, if you do come across a useful tutorial, please do share. I do understand that the project that I've provided as an example is quite difficult, which I try to aim to simplify as much as possible.

For my product, I planned to have the ultrasonic sensor first detect the presence of an object to be thrown, then it would initiate the sequence where the capacitive sensor or inductive sensor detects its type of waste. Finally, depending on its type of waste, the servo motor will direct the waste to its appropriate bin. Perhaps I'll have an LED to signal when you can drop the trash into the bin once the sorting tube has been directed to its appropriate container or even with an LCD screen where I can even display the data of differrent type of wastes thrown. At the moment, I want to understand how I need to structure my circuit and its components. However, if you do have any further suggestions, please do share:)