AVR DTMF Dialer
The high-fidelity AVR DTMF Dialer is a DTMF generator with a D-class power amplifier. The ATtiny26 microcontroller-based design saves on power—consuming only 1 µA in Standby mode and 25 mA in Active mode—and leaves a small footprint.
Link: http://www.circuitcellar.com/avr2004/DA3713.html
The high-fidelity AVR DTMF Dialer is a DTMF generator with a D-class power amplifier. The ATtiny26 microcontroller-based design saves on power—consuming only 1 µA in Standby mode and 25 mA in Active mode—and leaves a small footprint.
Link: http://www.circuitcellar.com/avr2004/DA3713.html