I am preparing to publish a technical book on programming that contains figures and charts (like, compiler, linker, ASCII table, keywords list) created by myself by taking references from many sources. Can I still need copyright clearance for using them in my book as the diagrams and charts are not originally designed by mine? Is the common conceptual figures like flowcharts of compilers, and list of programming keywords or ASCII table comes under copyright?
Putvi's answer is basically correct, but there are some points that should be further elaborated on. This is a flow chart that reduces a concept to a standard notation. Use of boxes, ellipses, diamonds, lines etc. a conventional way to express certain ideas, and the shapes themselves are ancient so not protected. The same is true of many mathematical equations or structural formulae in chemistry. However, those ideas have often been instantiated in publications with the element of creativity required for copyright protection: a flowchart could be a piece of art (that is how graphic designers see their work product). Directly copying that artwork would be infringement of the artist's copyright. Since the ideas which the art expresses are unprotected, you can create your own art following standard conventions, and the result will look very similar to the protected artwork in a published book. That similarity is because there are very limited possibilities for variation, under those standards. A publisher may, however, insist that you get permission from an author, if they are not familiar with the presentation standards in your field (so you may have to argue with the publisher).
The information in the Ascii table is not copyrighted, but specific charts containing that information may be copyrighted if they have a unique layout or design.
If the charts are made by you and are not someone else's work, the information itself is not copyrighted and you are safe.