We’re all familiar with IVRS systems that let you access
information using a touch-tone telephone. [Achu Wilso] built his
own version which uses a cellphone, microcontroller, and
computer. The cellphone is monitored by an LM324 op-amp with an
attached 555 timer chip. When a call comes in the voltage on the
headphone output goes high, activating the timer circuit. If it
goes low and does not go high again for about 25 seconds the
call will be ended. Each incoming touch tone acts as a keepalive
for the circuit. An MT8870 DTMF (touch tone) decoder chip
monitors the user input. An ATmega8 microcontroller grabs the
decoded touch tones from that chip, and pushes them to a PC via
USB. The PC-side software is written in Python, using MySQL
bindings to access database information. eSpeak, the open source
speech synthesizer software is used to read menu and database
information back to the caller. Not a bad little system, we wish
there was an audio clip so we could hear it in action.