TDD-filtering and demodulation in acoustically coupled modem
Eliana M. Klier, J Hrubý, M. Oklusky · 1989
The Czechoslovak Association of the Handicapped asked the authors to help deaf people by designing an economical TDD (Telephone Device for the Deaf). Among Czechoslovak deaf the SINCLAIR ZX SPECTRUM (with the Z 80 microprocessor) is widely used. Therefore the authors have decided to implement TDD as a peripheral device to this microcomputer. There exists a great variety of possible solutions with different weight given to software and hardware parts.