I would like to learn more about the design of digital cameras in general, and DSLR in particular, from optics to sensors to mounts.
Do you know any up-to-date resources (other than Wikipedia) where I can find some information about those subjects?
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The website Cambridge in Colour has a series of tutorials that cover everything from camera basics up through some more advanced topics on optics and sensors. Their focus is on providing education to help improve photographic skill, but they lay a good technical foundation in the process.
This site right here! Stack Exchange sites aren't really very well suited to "list o' resources" questions. Google is better for that, and always will be. But Photo-SE is well-suited to being such a resource. In fact, that's exactly what it's for.
If you have actual questions about specific things which aren't answered here already, please ask them (as individual new questions), and you should get good answers.