Patent US 4,754,474

A telecommunication method and apparatus for the deaf and hearing impaired uses the discrete dual frequency tones produced by each button on a telephone key pad to represent one of three letters inscribed on each key. Apparatus at the deaf person's receiving telephone assembles the sequences of number values identifying each letter group containing each letter in a transmitted word. Comparison apparatus within the receiving apparatus, preferably controlled by a microprocessor, compares the sequences of letter groups with allowed sequences of letter groups corresponding to pre-determined words stored within an electronic dictionary memory within the apparatus. When a perfect match has been obtained, the word interpreted from each triply ambiguous letter group corresponding to each transmitted letter is displaying visually on a CRT for the deaf person. Under microprocessor control, this procedure takes a fraction of a second per word lookup.