Chinese characters cannot be faithfully constructed backwards from a tone+syllable combination -- the mapping only goes one way (and even then, sometimes characters have multiple pronunciations).
There is no way to automatically convert pinyin into Chinese characters, especially if you don't have the tones. You can look them up individually on nciku, but you'll have no way of knowing which of the dozens of characters with the same pronunciation are the right ones.
I'm wondering if there is any way to write Chinese characters using the Latin alphabet (a-zA-Z) with/without accents of any sort, and then convert it into Chinese characters. Even if it is considered a bad idea for a new learner, I would still like to know if it is possible in any way.
If find it interesting when they say:
As you amass a vocabulary, you will start to notice patterns that will give you an intuition for which character is meant by the English pinyin, with or without tone markings.
In fact, even words like 终止 and 中止 sound identical with tones, so you only distinguish them in writing.
But in speech, you don't have access to writing, so this either means you need to learn how to read Chinese in order to understand these words in speech, or you can understand them in speech without learning to read Chinese, because of context of some sort.
If humans are able to tell how the sound of words translates into meaning, then I would wonder how we do that, because that would also answer the question.