Well it seems like a reasonable start; once you've added the other 99.99999999999999% (probably more 9s needed) of relevant info to the site then maybe it'll be worth another visit.
But why is it ad-supported already? Most non-commercial web sites are run by people who don't want ads and who pay for the site out of their own pockets, only resorting to ads after appealing to regulars for donations and not getting enough. There's not enough of your site yet to cost more than a few quid a year in hosting charges (hint: to save cash don't use ".com", use a local address instead).
Personally it's not a site I'd bother using; everything you've got is already in Wikipedia or can easily be found by plugging the appropriate terms into Google, so rather than doing your own thing and reinventing the wheel, which at the moment seems little more than a blog, why not work with an existing documentation site to improve what they've got? And if you do want to write a blog, use a blogging site; it'll be far easier.
Plus there are inaccuracies in your comments; take your ASCII table for example "it shouldn't contain any characters lower than 0x20. Those are all special characters, and have nothing to do in a text file." Nope, sorry, you can use all 256 characters in a text file IF they are appropriate. So if you want a beep, you include 7; a vertical tab 11; if you're sending escape codes to a terminal then obviously you need escape plus whatever characters make up the command which can quite reasonably include any 8-bit value from 0-256.
Hex, decimal, binary named "the 3 main systems". Er, no. There is an infinite number of number bases (aleph-1); if there is a main one then it's decimal but that's simply because we have 10 fingers and are biased. There are three that are common in IT; they are hex, binary and octal. Octal is significant because each octal digit corresponds to three bits and in C you can use octal directly by prefixing a number with 0, e.g. int i=012; printf("%d",i); will print 10. But you are correct in saying that hex is easier to use than binary.
"Hexadecimal numbers are the perfect compromise". Nope. What do you spend most of your time writing, as a programmer? Is it hex numbers, or do you use symbols instead, such as main, printf, fgets and so on? Hex numbers are a tiny step higher than binary, but they are by no means the perfect compromise; symbolic constants are a far better representation.
The whole site comes across as rather basic; I was a lot more critical before I had a look at bitmatic.com. I'd suggest you hang the references off bitmatic.com instead, maybe bitmatic.com/codecharts, but if I were a potential customer of yours looking at codecharts.com as an example of your work I'd probably continue shopping. Don't bother with the hints and tips and opinions, it makes you come across very much as a beginner. Looking at your main site and CV I'd say codecharts.com is most likely a very poor representation of your abilities.