This Speaking Calculator project is an interesting device built just by three chips that can be very useful to blind people. The system has four basic operations (addition, subtraction, multiplication and division), and the functions: clear all, change of sign (+/-), inverse (1/x), square root (v), pi number (p), add with memory (M+) and read from memory (MR). It also has the keys POWER_ON, POWER_OFF and VOICE to change between the Voice and No-voice modes. It works with a battery of 3 volts.
Main component of the system is the AVR ATmega88 microcontroller which has role reading the keypad, doing mathematical calculations, showing the results, voice generating and the handling of the battery energy in order to increase its lifetime. The system uses a two-wire serial EEPROM, AT24C1024, that contains the codified sound that the computer uses to communicate the results and to inform on the keys pressed by the human operator.
The Talking Calculator uses the speech waveform encoder RC-2 that needs only two resistors and one capacitor to do voice decoding. The LM4861, an Audio Power Amplifier with Shutdown Mode, is used to amplify the sound. To show the results we use a 3V alphanumeric LCD MDLS16166 of 16 characters x 1 line. The talking calculator is designed by Mariano Barron Ruiz from Spain.