Posted on Jan 14, 2013 4925
This text-to-speech converter is built around the SP0256-AL2 speech processor and the Cf6256AL2 text-to-speech converter chips~manufactured by General Instruments. The circuit is set up to receive standard ASCII code from virtually any microcomputer or dumb tenninal that is equipped with an RS-232 port -such as a serial-printer or modem port. If a microcomputer is used, the synthesizer can be activated from a terminal-emulator of any communications program, or from any programming language such as BASIC.
The serial input from the RS-232 port enters the circuit through U7. the MC1489 RS-232 receiver chip, and is converted from an RS-232 level to a TTL-level signal. The CTS256-AL2 chip, Ul, then converts the ASCII characters into allophone codes and sends those codes to U3, the TMS4016 externalRAM chip. The codes are then transferred to the SP0256-AL2, U2, through the 74LS373 octal latch, U4. Finally, the SP0256-AL2 sends out an audio signal to the LM386 audio amplifier, US, through some highpass filtering, and on to the speaker. The 74LS138d, US, and the 74LS04, U6, provide control logic.